Starch chemical properties

Starch chemical properties DEFAULT

Starch

Glucose polymer used as energy store in plants

For the Urhobo cuisine dish known as starch, see Usi (food). For the video game, see Starch (video game).

Chemical compound

Starch or amylum is a polymericcarbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets, and is contained in large amounts in staple foods like wheat, potatoes, maize (corn), rice, and cassava (manioc).

Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and helicalamylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.[4]Glycogen, the glucose store of animals, is a more highly branched version of amylopectin.

In industry, starch is converted into sugars, for example by malting, and fermented to produce ethanol in the manufacture of beer, whisky and biofuel. It is processed to produce many of the sugars used in processed foods. Mixing most starches in warm water produces a paste, such as wheatpaste, which can be used as a thickening, stiffening or gluing agent. The greatest industrial non-food use of starch is as an adhesive in the papermaking process. Starch solution may be applied to certain textile goods before ironing, to stiffen them.

Etymology[edit]

The word "starch" is from its Germanic root with the meanings "strong, stiff, strengthen, stiffen".[5] Modern German Stärke (strength) is related and referring for centuries main application, the use in textile: sizingyarn for weaving and starching linen. The Greek term for starch, "amylon" (ἄμυλον), which means "not milled", is also related. It provides the root amyl, which is used as a prefix for several 5-carbon compounds related to or derived from starch (e.g. amyl alcohol).

History[edit]

Starch grains from the rhizomes of Typha (cattails, bullrushes) as flour have been identified from grinding stones in Europe dating back to 30, years ago.[6] Starch grains from sorghum were found on grind stones in caves in Ngalue, Mozambique dating up to , years ago.[7]

Pure extracted wheat starch paste was used in Ancient Egypt possibly to glue papyrus.[8] The extraction of starch is first described in the Natural History of Pliny the Elder around AD 77–[9] Romans used it also in cosmetic creams, to powder the hair and to thicken sauces. Persians and Indians used it to make dishes similar to gothumai wheat halva. Rice starch as surface treatment of paper has been used in paper production in China since CE.[10]

Starch industry[edit]

In addition to starchy plants consumed directly, by 66 million tonnes of starch were being produced per year worldwide. In , production was increased to 73 million ton.[11]

In the EU the starch industry produced about million tonnes in , with around 40% being used for industrial applications and 60% for food uses,[12] most of the latter as glucose syrups.[13] In EU production was 11 million ton of which 9,4 million ton was consumed in the EU and of which 54% were starch sweeteners.[14]

The US produced about million tons of starch in , of which about million tons was high fructose syrup, million tons was glucose syrups, and million tons were starch products.[clarification needed] The rest of the starch was used for producing ethanol ( billion gallons).[15][16]

Energy store of plants[edit]

potato starch granules in cellsof the potato
starch in endosperm in embryonic phase of maize seed

Most green plants store energy as starch, which is packed into semicrystalline granules.[17] The extra glucose is changed into starch which is more complex than the glucose produced by plants. Young plants live on this stored energy in their roots, seeds, and fruits until it can find suitable soil in which to grow.[18] An exception is the family Asteraceae (asters, daisies and sunflowers), where starch is replaced by the fructaninulin. Inulin-like fructans are also present in grasses such as wheat, in onions and garlic, bananas, and asparagus.[19]

In photosynthesis, plants use light energy to produce glucose from carbon dioxide. The glucose is used to generate the chemical energy required for general metabolism, to make organic compounds such as nucleic acids, lipids, proteins and structural polysaccharides such as cellulose, or is stored in the form of starch granules, in amyloplasts. Toward the end of the growing season, starch accumulates in twigs of trees near the buds. Fruit, seeds, rhizomes, and tubers store starch to prepare for the next growing season.

Glucose is soluble in water, hydrophilic, binds with water and then takes up much space and is osmotically active; glucose in the form of starch, on the other hand, is not soluble, therefore osmotically inactive and can be stored much more compactly. The semicrystalline granules generally consist of concentric layers of amylose and amylopectin which can be made bioavailable upon cellular demand in the plant.[20]

Glucose molecules are bound in starch by the easily hydrolyzedalpha bonds. The same type of bond is found in the animal reserve polysaccharide glycogen. This is in contrast to many structural polysaccharides such as chitin, cellulose and peptidoglycan, which are bound by beta bonds and are much more resistant to hydrolysis.[21]

Biosynthesis[edit]

Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the enzyme glucosephosphate adenylyltransferase. This step requires energy in the form of ATP. The enzyme starch synthase then adds the ADP-glucose via a 1,4-alpha glycosidic bond to a growing chain of glucose residues, liberating ADP and creating amylose. The ADP-glucose is almost certainly added to the non-reducing end of the amylose polymer, as the UDP-glucose is added to the non-reducing end of glycogen during glycogen synthesis.[22]

Starch branching enzyme introduces 1,6-alpha glycosidic bonds between the amylose chains, creating the branched amylopectin. The starch debranching enzyme isoamylase removes some of these branches. Several isoforms of these enzymes exist, leading to a highly complex synthesis process.[23]

Glycogen and amylopectin have similar structure, but the former has about one branch point per ten 1,4-alpha bonds, compared to about one branch point per thirty 1,4-alpha bonds in amylopectin.[24] Amylopectin is synthesized from ADP-glucose while mammals and fungi synthesize glycogen from UDP-glucose; for most cases, bacteria synthesize glycogen from ADP-glucose (analogous to starch).[25]

In addition to starch synthesis in plants, starch can be synthesized from non-food starch mediated by an enzyme cocktail.[26] In this cell-free biosystem, beta-1,4-glycosidic bond-linked cellulose is partially hydrolyzed to cellobiose. Cellobiose phosphorylase cleaves to glucose 1-phosphate and glucose; the other enzyme—potato alpha-glucan phosphorylase can add a glucose unit from glucose 1-phosphorylase to the non-reducing ends of starch. In it, phosphate is internally recycled. The other product, glucose, can be assimilated by a yeast. This cell-free bioprocessing does not need any costly chemical and energy input, can be conducted in aqueous solution, and does not have sugar losses.[27][28][29]

Degradation[edit]

Starch is synthesized in plant leaves during the day and stored as granules; it serves as an energy source at night. The insoluble, highly branched starch chains have to be phosphorylated in order to be accessible for degrading enzymes. The enzyme glucan, water dikinase (GWD) phosphorylates at the C-6 position of a glucose molecule, close to the chains 1,6-alpha branching bonds. A second enzyme, phosphoglucan, water dikinase (PWD) phosphorylates the glucose molecule at the C-3 position. A loss of these enzymes, for example a loss of the GWD, leads to a starch excess (sex) phenotype,[30] and because starch cannot be phosphorylated, it accumulates in the plastids.

After the phosphorylation, the first degrading enzyme, beta-amylase (BAM) can attack the glucose chain at its non-reducing end. Maltose is released as the main product of starch degradation. If the glucose chain consists of three or fewer molecules, BAM cannot release maltose. A second enzyme, disproportionating enzyme-1 (DPE1), combines two maltotriose molecules. From this chain, a glucose molecule is released. Now, BAM can release another maltose molecule from the remaining chain. This cycle repeats until starch is degraded completely. If BAM comes close to the phosphorylated branching point of the glucose chain, it can no longer release maltose. In order for the phosphorylated chain to be degraded, the enzyme isoamylase (ISA) is required.[31]

The products of starch degradation are predominantly maltose[32] and smaller amounts of glucose. These molecules are exported from the plastid to the cytosol, maltose via the maltose transporter, which if mutated (MEX1-mutant) results in maltose accumulation in the plastid.[33] Glucose is exported via the plastidic glucose translocator (pGlcT).[34] These two sugars act as a precursor for sucrose synthesis. Sucrose can then be used in the oxidative pentose phosphate pathway in the mitochondria, to generate ATP at night.[31]

Properties[edit]

Structure[edit]

Corn starch, x magnified, under polarized light, showing characteristic extinction cross
Ricestarch seen on light microscope. Characteristic for the rice starch is that starch granules have an angular outline and some of them are attached to each other and form larger granules

While amylose was thought to be completely unbranched, it is now known that some of its molecules contain a few branch points.[35] Amylose is a much smaller molecule than amylopectin. About one quarter of the mass of starch granules in plants consist of amylose, although there are about times more amylose than amylopectin molecules.

Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size: rice starch is relatively small (about 2&#;μm) while potato starches have larger granules (up to &#;μm).

Some cultivated plant varieties have pure amylopectin starch without amylose, known as waxy starches. The most used is waxy maize, others are glutinous rice and waxy potato starch. Waxy starches have less retrogradation, resulting in a more stable paste. High amylose starch, amylomaize, is cultivated for the use of its gel strength and for use as a resistant starch (a starch that resists digestion) in food products.

Synthetic amylose made from cellulose has a well-controlled degree of polymerization. Therefore, it can be used as a potential drug deliver carrier.[26]

Dissolution and gelatinization[edit]

When being heated in abundant water, the granules of native starch swell and burst, the semi-crystalline structure is lost, and the smaller amylose molecules start leaching out of the granule, forming a network that holds water and increasing the mixture's viscosity. This process is called starch gelatinization. The gelatinization temperature of starch varies depending on starch cultivar, amylose/amylopectin content, and water content. Starch with water could experience complex multiphase transitions during differential scanning calorimetry (DSC) temperature scanning.[36] For starch with excess water, a single gelatinisation endotherm can be usually observed in the low temperature range (54–73 °C).[36] By reducing the water content (<64%) in starch, more endothermic transitions representing different structural changes can be seen because they become separated and they will move to higher temperatures.[36][37] With limited water content, the swelling forces will be much less significant, and the process of gelatinization in a low moisture content environment could more accurately be defined as the “melting” of starch.[38] Besides, the number of endotherms and enthalpies depended on amylose/amylopectin ratio, and the gelatinisation enthalpy of the amylopectin-rich starch was higher than that of the amylose-rich starch.[37] Specifically, waxy and normal maize starches show a large gelatinization endotherm at about 70 °C; for normal maize starches, there was also a second endotherm at about 90 °C, considered as the phase transition within an amylose–lipid complex; In contrast, for high-amylose content starches (e.g. Gelose 50 and Gelose 80), there is a very broad endotherm in the temperature range between 65 and °C, which is composed of the main gelatinization endotherm and the phase transition within an amylose–lipid complex.[37]

During cooking, the starch becomes a paste and increases further in viscosity. During cooling or prolonged storage of the paste, the semi-crystalline structure partially recovers and the starch paste thickens, expelling water. This is mainly caused by retrogradation of the amylose. This process is responsible for the hardening of bread or staling, and for the water layer on top of a starch gel (syneresis).

Certain starches, when mixed with water, will produce a non-Newtonian fluid sometimes nicknamed "oobleck".

Starch can also be dissolved or undergo gelation in ionic liquids or metal chloride salt solutions. The thermal transition of starch is largely influenced by the ratio of ionic liquid/water. Aqueous ionic liquid with a certain ionic liquid/water ratio leads to the most effective structural disorganisation of some starches at significantly reduced temperature (even at room temperature).[39][40] This phenomenon is very different from the dissolution of cellulose, as the latter occurs most efficiently in pure ionic liquids and any water contained in the ionic liquids will hinder the dissolution significantly.[41] It is proposed that for starches with granule surface pores (e.g. millet, waxy maize, normal maize and wheat starches), the corrosion by the aqueous IL follows an inside-out pattern and the destruction to the granules is fast and even, whereas for starches with a relatively smooth surface (e.g. high-amylose maize, potato, purple yam and pea starches), the corrosion can only start from the surface and thus the change caused the aqueous IL is slow.[42] Besides, starch, even high-amylose starch, can be fully dissolved by aqueous metal chloride salts (e.g. ZnCl2, CaCl2, and MgCl2) at moderate temperature (≤50 °C), and starch nanoparticles can form during this dissolution process.[43][44]

Hydrolysis[edit]

The enzymes that break down or hydrolyze starch into the constituent sugars are known as amylases.

Alpha-amylases are found in plants and in animals. Human saliva is rich in amylase, and the pancreas also secretes the enzyme. Individuals from populations with a high-starch diet tend to have more amylase genes than those with low-starch diets;[45]

Beta-amylase cuts starch into maltose units. This process is important in the digestion of starch and is also used in brewing, where amylase from the skin of seed grains is responsible for converting starch to maltose (Malting, Mashing).[46][47]

Given a heat of combustion of glucose of 2, kilojoules per mole (&#;kcal/mol) whereas that of starch is 2,&#;kJ (&#;kcal)[2] per mole of glucose monomer, hydrolysis releases about 30&#;kJ (&#;kcal) per mole, or &#;J (40&#;cal) per gram of glucose product.

Dextrinization[edit]

If starch is subjected to dry heat, it breaks down to form dextrins, also called "pyrodextrins" in this context. This break down process is known as dextrinization. (Pyro)dextrins are mainly yellow to brown in color and dextrinization is partially responsible for the browning of toasted bread.[48]

Chemical tests[edit]

Main article: Iodine test

Granules of wheat starch, stained with iodine, photographed through a light microscope

A triiodide (I3) solution formed by mixing iodine and iodide (usually from potassium iodide) is used to test for starch; a dark blue color indicates the presence of starch. The details of this reaction are not fully known, but recent scientific work using single crystal x-ray crystallography and comparative Raman spectroscopy suggests that the final starch-iodine structure is similar to an infinite polyiodide chain like one found in a pyrroloperylene-iodine complex.[49] The strength of the resulting blue color depends on the amount of amylose present. Waxy starches with little or no amylose present will color red. Benedict's test and Fehling's test is also done to indicate the presence of starch.

Starch indicator solution consisting of water, starch and iodide is often used in redox titrations: in the presence of an oxidizing agent the solution turns blue, in the presence of reducing agent the blue color disappears because triiodide (I3) ions break up into three iodide ions, disassembling the starch-iodine complex. Starch solution was used as indicator for visualizing the periodic formation and consumption of triiodide intermediate in the Briggs-Rauscher oscillating reaction. The starch, however, changes the kinetics of the reaction steps involving triiodide ion.[50] A % w/w solution is the standard concentration for a starch indicator. It is made by adding 3&#;grams of soluble starch to 1 liter of heated water; the solution is cooled before use (starch-iodine complex becomes unstable at temperatures above 35&#;°C).

Each species of plant has a unique type of starch granules in granular size, shape and crystallization pattern. Under the microscope, starch grains stained with iodine illuminated from behind with polarized light show a distinctive Maltese cross effect (also known as extinction cross and birefringence).

Food[edit]

Sago starch extraction from palm stems

Starch is the most common carbohydrate in the human diet and is contained in many staple foods. The major sources of starch intake worldwide are the cereals (rice, wheat, and maize) and the root vegetables (potatoes and cassava).[51] Many other starchy foods are grown, some only in specific climates, including acorns, arrowroot, arracacha, bananas, barley, breadfruit, buckwheat, canna, colocasia, katakuri, kudzu, malanga, millet, oats, oca, polynesian arrowroot, sago, sorghum, sweet potatoes, rye, taro, chestnuts, water chestnuts and yams, and many kinds of beans, such as favas, lentils, mung beans, peas, and chickpeas.

Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta, porridge and tortilla.

Digestive enzymes have problems digesting crystalline structures. Raw starch is digested poorly in the duodenum and small intestine, while bacterial degradation takes place mainly in the colon. When starch is cooked, the digestibility is increased.

Starch gelatinization during cake baking can be impaired by sugar competing for water, preventing gelatinization and improving texture.

Before the advent of processed foods, people consumed large amounts of uncooked and unprocessed starch-containing plants, which contained high amounts of resistant starch. Microbes within the large intestine fermented the starch, produced short-chain fatty acids, which are used as energy, and support the maintenance and growth of the microbes. More highly processed foods are more easily digested and release more glucose in the small intestine—less starch reaches the large intestine and more energy is absorbed by the body. It is thought that this shift in energy delivery (as a result of eating more processed foods) may be one of the contributing factors to the development of metabolic disorders of modern life, including obesity and diabetes.[52]

The amylose/amylopectin ratio, molecular weight and molecular fine structure influences the physicochemical properties as well as energy release of different types of starches.[53] In addition, cooking and food processing significantly impacts starch digestibility and energy release. Starch can be classified as rapidly digestible, slowly digestible and resistant starch.[54] Raw starch granules resist digestion by human enzymes and do not break down into glucose in the small intestine - they reach the large intestine instead and function as prebioticdietary fiber.[55] When starch granules are fully gelatinized and cooked, the starch becomes easily digestible and releases glucose quickly within the small intestine. When starchy foods are cooked and cooled, some of the glucose chains re-crystallize and become resistant to digestion again. Slowly digestible starch can be found in raw cereals, where digestion is slow but relatively complete within the small intestine.[54]

Starch production[edit]

The starch industry extracts and refines starches from seeds, roots and tubers, by wet grinding, washing, sieving and drying. Today, the main commercial refined starches are cornstarch, tapioca, arrowroot,[56] and wheat, rice, and potato starches. To a lesser extent, sources of refined starch are sweet potato, sago and mung bean. To this day, starch is extracted from more than 50 types of plants.

Untreated starch requires heat to thicken or gelatinize. When a starch is pre-cooked, it can then be used to thicken instantly in cold water. This is referred to as a pregelatinized starch.

Starch sugars[edit]

Karo corn syrup advert
Niagara corn starch advert s
Pacific Laundry and Cooking Starch advert

Starch can be hydrolyzed into simpler carbohydrates by acids, various enzymes, or a combination of the two. The resulting fragments are known as dextrins. The extent of conversion is typically quantified by dextrose equivalent (DE), which is roughly the fraction of the glycosidic bonds in starch that have been broken.

These starch sugars are by far the most common starch based food ingredient and are used as sweeteners in many drinks and foods. They include:

  • Maltodextrin, a lightly hydrolyzed (DE 10–20) starch product used as a bland-tasting filler and thickener.
  • Various glucose syrups (DE 30–70), also called corn syrups in the US, viscous solutions used as sweeteners and thickeners in many kinds of processed foods.
  • Dextrose (DE ), commercial glucose, prepared by the complete hydrolysis of starch.
  • High fructose syrup, made by treating dextrose solutions with the enzyme glucose isomerase, until a substantial fraction of the glucose has been converted to fructose. In the U.S. high-fructose corn syrup is significantly cheaper than sugar, and is the principal sweetener used in processed foods and beverages.[57] Fructose also has better microbiological stability. One kind of high fructose corn syrup, HFCS, is sweeter than sucrose because it is made with more fructose, while the sweetness of HFCS is on par with sucrose.[58][59]
  • Sugar alcohols, such as maltitol, erythritol, sorbitol, mannitol and hydrogenated starch hydrolysate, are sweeteners made by reducing sugars.

Modified starches[edit]

A modified starch is a starch that has been chemically modified to allow the starch to function properly under conditions frequently encountered during processing or storage, such as high heat, high shear, low pH, freeze/thaw and cooling.

The modified food starches are E coded according to European Food Safety Authority and INS coded Food Additives according to the Codex Alimentarius:[60]

  • Dextrin
  • Acid-treated starch
  • Alkaline-treated starch
  • Bleached starch
  • Oxidized starch
  • Starches, enzyme-treated
  • Monostarch phosphate
  • Distarch phosphate
  • Phosphated distarch phosphate
  • Acetylated distarch phosphate
  • Starch acetate
  • Acetylated distarch adipate
  • Hydroxypropyl starch
  • Hydroxypropyl distarch phosphate
  • Hydroxypropyl distarch glycerol
  • Starch sodium octenyl succinate
  • Acetylated oxidized starch

INS , , , and are in the EU food ingredients without an E-number.[61] Typical modified starches for technical applications are cationic starches, hydroxyethyl starch and carboxymethylated starches.

Use as food additive[edit]

As an additive for food processing, food starches are typically used as thickeners and stabilizers in foods such as puddings, custards, soups, sauces, gravies, pie fillings, and salad dressings, and to make noodles and pastas. They function as thickeners, extenders, emulsion stabilizers and are exceptional binders in processed meats.

Gummed sweets such as jelly beans and wine gums are not manufactured using a mold in the conventional sense. A tray is filled with native starch and leveled. A positive mold is then pressed into the starch leaving an impression of 1, or so jelly beans. The jelly mix is then poured into the impressions and put onto a stove to set. This method greatly reduces the number of molds that must be manufactured.

Use in pharmaceutical industry[edit]

In the pharmaceutical industry, starch is also used as an excipient, as tablet disintegrant, and as binder.

Resistant starch[edit]

Main article: Resistant starch

Resistant starch is starch that escapes digestion in the small intestine of healthy individuals. High-amylose starch from corn has a higher gelatinization temperature than other types of starch, and retains its resistant starch content through baking, mild extrusion and other food processing techniques. It is used as an insoluble dietary fiber in processed foods such as bread, pasta, cookies, crackers, pretzels and other low moisture foods. It is also utilized as a dietary supplement for its health benefits. Published studies have shown that resistant starch helps to improve insulin sensitivity,[62] increases satiety,[63] reduces pro-inflammatory biomarkers interleukin 6 and tumor necrosis factor alpha[64] and improves markers of colonic function.[65] It has been suggested that resistant starch contributes to the health benefits of intact whole grains.[66]

Non-food applications[edit]

Gentleman with starched ruff in

Papermaking[edit]

Papermaking is the largest non-food application for starches globally, consuming many millions of metric tons annually.[12] In a typical sheet of copy paper for instance, the starch content may be as high as 8%. Both chemically modified and unmodified starches are used in papermaking. In the wet part of the papermaking process, generally called the "wet-end", the starches used are cationic and have a positive charge bound to the starch polymer. These starch derivatives associate with the anionic or negatively charged paper fibers / cellulose and inorganic fillers. Cationic starches together with other retention and internal sizing agents help to give the necessary strength properties to the paper web formed in the papermaking process (wet strength), and to provide strength to the final paper sheet (dry strength).

In the dry end of the papermaking process, the paper web is rewetted with a starch based solution. The process is called surface sizing. Starches used have been chemically, or enzymatically depolymerized at the paper mill or by the starch industry (oxidized starch). The size/starch solutions are applied to the paper web by means of various mechanical presses (size presses). Together with surface sizing agents the surface starches impart additional strength to the paper web and additionally provide water hold out or "size" for superior printing properties. Starch is also used in paper coatings as one of the binders for the coating formulations which include a mixture of pigments, binders and thickeners. Coated paper has improved smoothness, hardness, whiteness and gloss and thus improves printing characteristics.

Corrugated board adhesives[edit]

Corrugated board adhesives are the next largest application of non-food starches globally. Starch glues are mostly based on unmodified native starches, plus some additive such as borax and caustic soda. Part of the starch is gelatinized to carry the slurry of uncooked starches and prevent sedimentation. This opaque glue is called a SteinHall adhesive. The glue is applied on tips of the fluting. The fluted paper is pressed to paper called liner. This is then dried under high heat, which causes the rest of the uncooked starch in glue to swell/gelatinize. This gelatinizing makes the glue a fast and strong adhesive for corrugated board production.

Clothing starch[edit]

Kingsford OswegoStarch advertising,

Clothing or laundry starch is a liquid prepared by mixing a vegetable starch in water (earlier preparations also had to be boiled), and is used in the laundering of clothes. Starch was widely used in Europe in the 16th and 17th centuries to stiffen the wide collars and ruffs of fine linen which surrounded the necks of the well-to-do. During the 19th and early 20th century it was stylish to stiffen the collars and sleeves of men's shirts and the ruffles of women's petticoats by starching them before the clean clothes were ironed. Starch gave clothing smooth, crisp edges, and had an additional practical purpose: dirt and sweat from a person's neck and wrists would stick to the starch rather than to the fibers of the clothing. The dirt would wash away along with the starch; after laundering, the starch would be reapplied. Starch is available in spray cans, in addition to the usual granules to mix with water.

Bioplastic[edit]

Bioplastic §&#;Starch-based plastics

Starch is an important natural polymer to make bioplastics. With water and plasticisers such as glycerol, starch can be processed into so-called "thermoplastic starch" using conventional polymer processing techniques such as extrusion, injection molding and compression molding.[67] Since materials based on only native starch have poor processibility, mechanical properties and stability, more commonly modified starches (e.g. hydroxypropyl starch) are used and starch is combined with other polymers (preferably biodegradable polymers such as polycaprolactone), as some commercial products (e.g. PLANTIC™ HP[68] and Mater-Bi®[69]) available on the market.

Other[edit]

Another large non-food starch application is in the construction industry, where starch is used in the gypsum wall board manufacturing process. Chemically modified or unmodified starches are added to the stucco containing primarily gypsum. Top and bottom heavyweight sheets of paper are applied to the formulation, and the process is allowed to heat and cure to form the eventual rigid wall board. The starches act as a glue for the cured gypsum rock with the paper covering, and also provide rigidity to the board.

Starch is used in the manufacture of various adhesives or glues[70] for book-binding, wallpaper adhesives, paper sack production, tube winding, gummed paper, envelope adhesives, school glues and bottle labeling. Starch derivatives, such as yellow dextrins, can be modified by addition of some chemicals to form a hard glue for paper work; some of those forms use borax or soda ash, which are mixed with the starch solution at 50–70&#;°C (–&#;°F) to create a very good adhesive. Sodium silicate can be added to reinforce these formula.

Occupational safety and health[edit]

In the US the Occupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for starch exposure in the workplace as 15&#;mg/m3 total exposure and 5&#;mg/m3 respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended exposure limit (REL) of 10&#;mg/m3 total exposure and 5&#;mg/m3 respiratory exposure over an 8-hour workday.[74]

See also[edit]

References[edit]

  1. ^Roy L. Whistler; James N. BeMiller; Eugene F. Paschall, eds. (). Starch: Chemistry and Technology. Academic Press. p.&#;
  2. ^ abCRC Handbook of Chemistry and Physics, 49th edition, , p. D
  3. ^NIOSH Pocket Guide to Chemical Hazards. "#". National Institute for Occupational Safety and Health (NIOSH).
  4. ^Brown, W. H.; Poon, T. (). Introduction to organic chemistry (3rd&#;ed.). Wiley. ISBN&#;.[page&#;needed]
  5. ^New Shorter Oxford Dictionary, Oxford,
  6. ^Revedin, A.; Aranguren, B.; Becattini, R.; Longo, L.; Marconi, E.; Lippi, M. M.; Skakun, N.; Sinitsyn, A.; et&#;al. (). "Thirty thousand-year-old evidence of plant food processing". Proceedings of the National Academy of Sciences. (44): –9. BibcodePNASR. doi/pnas PMC&#; PMID&#;
  7. ^"Porridge was eaten , years ago". The Telegraph. 18 Dec
  8. ^Pliny the Elder, The Natural History (Pliny), Book XIII, Chapter 26, The paste used in preparation of paper
  9. ^Pliny the Elder, The Natural History (Pliny), Book XIII, Chapter 17, [1]
  10. ^Hunter, Dard (). Papermaking. DoverPublications. p.&#; ISBN&#;.
  11. ^Starch Europe, AAF position on competitiveness, visited march 3
  12. ^ abNNFCC Renewable Chemicals Factsheet: Starch
  13. ^International Starch Institute Denmark, Starch production volume
  14. ^Starch Europe, Industry, visited march 3
  15. ^CRA, Industry overview , visited on march 3
  16. ^Starch Europe, Updated position on the EU-US Transatlantic Trade and Investment Partnership, visited on march 3
  17. ^Zobel, H.F. (). "Molecules to granules: a comprehensive starch review". Starch/Starke. 40 (2): 44– doi/star
  18. ^Bailey, E.H.S.; Long, W.S. (Jan 14, – Jan 13, ). "On the occurrence of starch in green fruits". Transactions of the Kansas Academy of Science. 28: – doi/ JSTOR&#;
  19. ^Vijn, Irma; Smeekens, Sjef (). "Fructan: more than a reserve carbohydrate?". Plant Physiology. (2): – doi/pp PMC&#; PMID&#;
  20. ^Blennow, Andreas; Engelsen, Soren B (10 Feb ). "Helix-breaking news: fighting crystalline starch energy deposits in the cell". Trends in Plant Science. 15 (4): – doi/j.tplants PMID&#;
  21. ^Zeeman, Samuel C.; Kossmann, Jens; Smith, Alison M. (June 2, ). "Starch: Its Metabolism, Evolution, and Biotechnological Modification in Plants". Annual Review of Plant Biology. 61 (1): – doi/annurev-arplant PMID&#;
  22. ^Nelson, D. () Lehninger Principles of Biochemistry, 6th ed., W.H. Freeman and Company (p. )
  23. ^Smith, Alison M. (). "The Biosynthesis of Starch Granules". Biomacromolecules. 2 (2): – doi/bmc. PMID&#;
  24. ^Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. (). "Section ". Biochemistry (5th&#;ed.). San Francisco: W.H. Freeman. ISBN&#;.
  25. ^Ball, Steven G.; Matthew K Morell (). "FROM BACTERIAL GLYCOGEN TO STARCH: Understanding the Biogenesis of the Plant Starch Granule". Annual Review of Plant Biology. 54 (1): – doi/annurev.arplant PMID&#;
  26. ^ abYou, C.; Chen, H.; Myung, S.; Sathitsuksanoh, N.; Ma, H.; Zhang, X.-Z.; Li, J.; Zhang, Y.- H. P. (April 15, ). "Enzymatic transformation of nonfood biomass to starch". Proceedings of the National Academy of Sciences. (18): – BibcodePNASY. doi/pnas PMC&#; PMID&#;
  27. ^"Chemical Process Creates Food Source from Plant Waste". Voice of America. April 16, Retrieved January 27,
  28. ^Zhang, Y.-H Percival (). "Next generation biorefineries will solve the food, biofuels, and environmental trilemma in the energy-food-water nexus". Energy Science. 1: 27– doi/ese
  29. ^Choi, Charles (April 15, ). "Could Wood Feed the World?". Science. Retrieved January 27,
  30. ^Yu, TS; Kofler, H; Häusler, RE; et&#;al. (August ). "The Arabidopsis sex1 mutant is defective in the R1 protein, a general regulator of starch degradation in plants, and not in the chloroplast hexose transporter"(PDF). Plant Cell. 13 (8): – doi/tpc PMC&#; PMID&#; Archived from the original(PDF) on Retrieved
  31. ^ abSmith, Alison M.; Zeeman, Samuel C.; Smith, Steven M. (). "Starch Degradation"(PDF). Annual Review of Plant Biology. 56: 73– doi/annurev.arplant PMID&#; Archived from the original(PDF) on Retrieved
  32. ^Weise, SE; Weber, AP; Sharkey, TD (). "Maltose is the major form of carbon exported from the chloroplast at night". Planta. (3): – doi/sy. PMID&#; S2CID&#;
  33. ^Purdy, SJ; Bussell, JD; Nunn, CP; Smith, SM (). "Leaves of the Arabidopsis maltose exporter1 mutant exhibit a metabolic profile with features of cold acclimation in the warm". PLOS ONE. 8 (11): e BibcodePLoSOP. doi/journal.pone PMC&#; PMID&#;
  34. ^Weber, A; Servaites, JC; Geiger, DR; et&#;al. (May ). "Identification, purification, and molecular cloning of a putative plastidic glucose translocator". Plant Cell. 12 (5): – doi/tpc PMC&#; PMID&#;
  35. ^David R. Lineback, "Starch", in [email protected]
  36. ^ abcLiu, Peng; Xie, Fengwei; Li, Ming; Liu, Xingxun; Yu, Long; Halley, Peter J.; Chen, Ling (). "Phase transitions of maize starches with different amylose contents in glycerol–water systems". Carbohydrate Polymers. 85 (1): – doi/j.carbpol ISSN&#;
  37. ^ abcLiu, Hongsheng; Yu, Long; Xie, Fengwei; Chen, Ling (). "Gelatinization of cornstarch with different amylose/amylopectin content". Carbohydrate Polymers. 65 (3): – doi/j.carbpol ISSN&#;
  38. ^Liu, Hongsheng; Xie, Fengwei; Yu, Long; Chen, Ling; Li, Lin (). "Thermal processing of starch-based polymers". Progress in Polymer Science. 34 (12): – doi/j.progpolymsci ISSN&#;
  39. ^Mateyawa, Sainimili; Xie, David Fengwei; Truss, Rowan W.; Halley, Peter J.; Nicholson, Timothy M.; Shamshina, Julia L.; Rogers, Robin D.; Boehm, Michael W.; McNally, Tony (). "Effect of the ionic liquid 1-ethylmethylimidazolium acetate on the phase transition of starch: Dissolution or gelatinization?". Carbohydrate Polymers. 94 (1): – doi/j.carbpol ISSN&#; PMID&#;
  40. ^Zhang, Binjia; Chen, Ling; Xie, Fengwei; Li, Xiaoxi; Truss, Rowan W.; Halley, Peter J.; Shamshina, Julia L.; Rogers, Robin D.; McNally, Tony (). "Understanding the structural disorganization of starch in water–ionic liquid solutions". Physical Chemistry Chemical Physics. 17 (21): – BibcodePCCPZ. doi/C5CPK. ISSN&#; PMID&#;
  41. ^Tan, Xiaoyan; Li, Xiaoxi; Chen, Ling; Xie, Fengwei (). "Solubility of starch and microcrystalline cellulose in 1-ethylmethylimidazolium acetate ionic liquid and solution rheological properties". Physical Chemistry Chemical Physics. 18 (39): – BibcodePCCPT. doi/C6CPC. ISSN&#; PMID&#;
  42. ^Zan, Ke; Wang, Jinwei; Ren, Fei; Yu, Jinglin; Wang, Shuo; Xie, Fengwei; Wang, Shujun (). "Structural disorganization of cereal, tuber and bean starches in aqueous ionic liquid at room temperature: Role of starch granule surface structure". Carbohydrate Polymers. : doi/j.carbpol ISSN&#; PMID&#; S2CID&#;
  43. ^Lin, Meiying; Shang, Xiaoqin; Liu, Peng; Xie, Fengwei; Chen, Xiaodong; Sun, Yongyi; Wan, Junyan (). "Zinc chloride aqueous solution as a solvent for starch". Carbohydrate Polymers. : – doi/j.carbpol ISSN&#; PMID&#;
  44. ^Li, Ying; Liu, Peng; Ma, Cong; Zhang, Na; Shang, Xiaoqin; Wang, Liming; Xie, Fengwei (). "Structural Disorganization and Chain Aggregation of High-Amylose Starch in Different Chloride Salt Solutions". ACS Sustainable Chemistry & Engineering. 8 (12): – doi/acssuschemeng.9b S2CID&#;
  45. ^Perry, George H; Dominy, Nathaniel J; Claw, Katrina G; Lee, Arthur S; Fiegler, Heike; Redon, Richard; Werner, John; Villanea, Fernando A; et&#;al. (). "Diet and the evolution of human amylase gene copy number variation". Nature Genetics. 39 (10): – doi/ng PMC&#; PMID&#;
  46. ^"Scope and Mechanism of Carbohydrase Action". The Journal of Biological Chemistry. .
  47. ^Marc, A.; Engasser, J. M.; Moll, M.; Flayeux, R. (). "A kinetic model of starch hydrolysis by α- and β-amylase during mashing". Biotechnology and Bioengineering. 25 (2): – doi/bit ISSN&#; PMID&#; S2CID&#;
  48. ^Ph.D, Judit E. Puskas (). Introduction to Polymer Chemistry: A Biobased Approach. DEStech Publications, Inc. p.&#; ISBN&#;.
  49. ^Madhu, Sheri; Evans, Hayden A.; Doan-Nguyen, Vicky V. T.; Labram, John G.; Wu, Guang; Chabinyc, Michael L.; Seshadri, Ram; Wudl, Fred (4 July ). "Infinite Polyiodide Chains in the Pyrroloperylene-Iodine Complex: Insights into the Starch-Iodine and Perylene-Iodine Complexes". Angewandte Chemie International Edition. 55 (28): – doi/anie PMID&#;
  50. ^Csepei, L. I.; Bolla, Cs. (). "IS STARCH ONLY A VISUAL INDICATOR FOR IODINE IN THE BRIGGS-RAUSCHER OSCILLATING REACTION?". STUDIA UNIVERSITATIS BABEŞ-BOLYAI Chemia (2): –
  51. ^Anne-Charlotte Eliasson (). Starch in food: Structure, function and applications. Woodhead Publishing. ISBN&#;
  52. ^Walter, Jens; Ley, Ruth (October ). "The Human Gut Microbiome: Ecology and Recent Evolutionary Changes". Annual Review of Microbiology. 65 (1): – doi/annurev-micro PMID&#;
  53. ^Lindeboom, Nienke; Chang, Peter R.; Tyler, Robert T. (1 Apr ). "Analytical, biochemical and physicochemical aspoects of starch granule size, with emphasis on small granule starches: a review". Starch-Stärke. 56 (3–4): 89– doi/star
  54. ^ abEnglyst, H.N.; Kingman, S.M.; Cummings, J.H. (Oct ). "Classification and measurement of nutritionally important starch fractions". European Journal of Clinical Nutrition. 46 (Suppl. 2): S PMID&#;
  55. ^Lockyer, S.; Nugent, A.P. (5 Jan ). "Health effects of resistant starch". Nutrition Bulletin. 42 (1): 10– doi/nbu
  56. ^Hemsley + Hemsley. "Arrowroot recipes". BBC Food. Retrieved 13 August
  57. ^Beverage daily: 'Sugar is much, much bigger': Rocketing HFCS prices don't spook Coke CEO
  58. ^Ophardt, Charles. "Sweetners – Introduction". Elmhurst College.
  59. ^White, John S. (December 2, ). "HFCS: How Sweet It Is".
  60. ^Modified Starches. CODEX ALIMENTARIUS published in FNP 52 Add 9 ()
  61. ^Database on Food Additives EU, visited December 6
  62. ^Maki, K. C.; Pelkman, C. L.; Finocchiaro, E. T.; Kelley, K. M.; Lawless, A. L.; Schild, A. L.; Rains, T. M. (). "Resistant Starch from High-Amylose Maize Increases Insulin Sensitivity in Overweight and Obese Men". Journal of Nutrition. (4): – doi/jn PMC&#; PMID&#;
  63. ^Bodinham, Caroline L.; Frost, Gary S.; Robertson, M. Denise (). "Acute ingestion of resistant starch reduces food intake in healthy adults"(PDF). British Journal of Nutrition. (6): – doi/S PMID&#;
  64. ^Vahdat, Mahsa; Hosseini, Seyed Ahmad; Khalatbari Mohseni, Golsa; Heshmati, Javad; Rahimlou, Mehran (15 Apr ). "Effects of resistant starch interventions on circulating inflammatory biomarkers: a systematic review and meta-analysis of randomized controlled trials". Nutrition Journal. 19 (1): Article doi/s PMC&#; PMID&#;
  65. ^Nugent, A. P. (). "Health properties of resistant starch". Nutrition Bulletin. 30: 27– doi/jx.
  66. ^Higgins, Janine A. (). "Whole Grains, Legumes, and the Subsequent Meal Effect: Implications for Blood Glucose Control and the Role of Fermentation". Journal of Nutrition and Metabolism. : 1–7. doi// PMC&#; PMID&#;
  67. ^Liu, Hongsheng; Xie, Fengwei; Yu, Long; Chen, Ling; Li, Lin (). "Thermal processing of starch-based polymers". Progress in Polymer Science. 34 (12): – doi/j.progpolymsci ISSN&#;
  68. ^"Plantic HP | Plantic". www.plantic.com.au. Retrieved
  69. ^"Mater-Bi - biodegradable and compostable bioplastics - Novamont". www.novamont.com. Retrieved
  70. ^"Stuck on Starch: A new wood adhesive". US Department of Agriculture.
  71. ^"Spray Powder". Russell-Webb. Archived from the original on Retrieved
  72. ^American coalition for ethanol, Ethanol facilities
  73. ^Zhang, Y.-H. Percival; Evans, Barbara R.; Mielenz, Jonathan R.; Hopkins, Robert C.; Adams, Michael W.W. (). Melis, Anastasios (ed.). "High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway". PLOS ONE. 2 (5): e BibcodePLoSOZ. doi/journal.pone PMC&#; PMID&#;
  74. ^"CDC – NIOSH Pocket Guide to Chemical Hazards – Starch". www.cdc.gov. Retrieved

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Sours: https://en.wikipedia.org/wiki/Starch

Chemical Properties of Starch and Its Application in the Food Industry

Open access peer-reviewed chapter

By Henry Omoregie Egharevba

Submitted: April 5th Reviewed: June 6th Published: August 5th

DOI: /intechopen

Abstract

Starch is an important food product and a versatile biomaterial used world-wide for different purposes in many industrial sectors including foods, health, textile, chemical and engineering sector. Starch versatility in industrial applications is largely defined by its physicochemical properties and functionality. Starch in its native form has limited functionality and application. But advancements in biotechnology and chemical technological have led to wide-range modification of starch for different purposes. The objective of this chapter is to examine the different chemical reactions of starch and expose the food applications of the modification products. Several literatures on starch and reaction chemistry including online journals and books were analyzed, harmonized and rationalized. The reactions and mechanisms presented are explained based on the principles of reaction chemistry. Chemical modification of starch is based on the chemical reactivity of the constituent glucose monomers which are polyhydroxyl and can undergo several reactions. Starch can undergo reactions such as hydrolysis, esterification, etherification and oxidation. These reactions give modified starches which can be used in baked foods, confectionaries, soups and salad dressings. This chapter discusses the different chemical reactions of starch, the associated changes in functionality, as well as the applications of chemically modified starches in the food industry.

Keywords

  • reactions of starch
  • hydrolysis
  • esterification
  • etherification
  • baked products
  • confectioneries
  • gravies
  • soups and sauces
  • mayonnaises and salad dressing

1. Introduction

Starch also known as amylum, is an important food product and biomaterial used world-wide for different purposes. Though traditionally used in the food industry, technological advancement has led to its steady relevance in many other sectors such as health and medicine, textile, paper, fine chemicals, petroleum engineering, agriculture, and construction engineering [1]. It is used in the food industry either as food products or additives for thickening, preservation and quality enhancer in baked foods, confectioneries, pastas, soups and sauces, and mayonnaises. Starch is a polysaccharide of glucose made of two types of α-d-glucan chains, amylose and amylopectin. Starch molecules produced by each plant species have specific structures and compositions (such as length of glucose chains or the amylose/amylopectin ratio), and the protein and fat content of the storage organs may vary significantly. Therefore, starch differs depending on the source. This inherent functional diversity due to the different biological sources enlarges its range of industrial uses [2, 3].

The structural and compositional differences in starches from different sources determine its properties and mode of interactions with other constituents of foods that gives the final product the desired taste and texture. In the food industry, starch can be used as a food additive to control the uniformity, stability and texture of soups and sauces, to resist the gel breakdown during processing and to raise the shelf life of products [2]. Starch is relatively easily extractable and does not require complicated purification processes. It is considered to be available in large quantities in major plant sources such as cereal grains and tubers. These sources are generally considered inexpensive and affordable and serve as raw materials for commercial production [4].

Starch from (corn, Figure 1) account for 80% of the world market production of starch. Maize starch is an important ingredient in the production of many food products, and has been widely used as a thickener, stabiliser, colloidal gelling agent, water retention agent and as an adhesive due to its very adaptive physicochemical characteristics [5]. Starches from tubers of roots such as potato tubers (Figure 1), which are considered non-conventional sources have found usefulness in providing options for extending the spectrum of desired functional properties, which are needed for added-value food product development.

The stability of native starch under different pH values and temperatures varies unfavorably. For instance, native starch granule is insoluble in water at room temperature and extremely resistant to hydrolysis by amylase. Hence native starch has limited functionality. In order to enhance properties and functionality such as solubility, texture, viscosity and thermal stability, which are necessary for the desired product or role in the industry, native starches are modified. The widening vista of application possibilities of starches with different properties has made research in non-conventional starches and other native starches more imperative [2, 6, 7]. Recent studies on the relationship between the structural characteristics and functional properties of starches from different sources have continued to provide important information for optimizing industrial applications.

Modification has been achieved mostly by physical and chemical means. Enzymic and genetic modifications are biotechnological processes which are increasingly being explored [8]. While physical modification methods seemed simple and cheap, such as superheating, dry heating, osmotic pressure treatment, multiple deep freezing and thawing, instantaneous controlled pressure-drop process, stirring ball milling, vacuum ball milling, pulsed electric fields treatment, corona electrical discharges, etc., chemical modification involves the introduction of new functional moieties into the starch molecule via its hydroxyl groups, resulting in marked change in its physicochemical characteristic. The functional characteristics of chemically modified starch depends on a number of factors including the botanic origin of the native starch, reagent used, concentration of reagent, pH, reaction time, the presence of catalyst, type of substituent, degree of substitution, and the distribution of the substituents in the modified starch molecule. Modification is generally achieved through chemical derivatization, such as etherification, esterification, acetylation, cationization, oxidation, hydrolysis, and cross-linking [7]. This chapter discusses the chemical properties of starch and how they determine its application in the food industry.

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2. Amylose and amylopectin

The chemical behaviour of starch is dependent on the nature of its constituent compounds. Starch is a homopolysaccharides made up of glucose units. However, the homopolysaccharide are of two types namely: amylose, which is a linear chain consisting of about – glucose units, and amylopectin, which is highly branched and consist of over 1,, glucose units. The two types of homopolysaccharides constitute approximately 98–99% of the dry weight of starch [2]. The ratio of the two polysaccharides usually varies depending on the botanical origin of the starch. Botanic source reports that starch chain generally consist of 20% amylose and up to 80% amylopectin by mass. It is believed that starch with up to 80% amylose can exist [7]. Some classification categorize starch containing <15% amylose as ‘waxy’, 20–35% as ‘normal’ and greater ≥40% as ‘high’ amylose starches [9].

Amylose and amylopectin have different physiochemical properties which impact on the overall properties of the starch. Hence it is often important to determine the concentration of each individual component of the starch, as well as the overall starch concentration [10]. The physicochemical (e.g., gelatinization and retrogradation) and functional (e.g., solubility, swelling, water absorption, syneresis and rheological behaviour of gels) properties determine the potential uses of starches in the food industry. These properties depend on the molecular and structural composition of amylose and amylopectin, percent composition and arrangement of these two homopolysaccharides in starch granules which often determine the granule size and shape depending on other genetic factors as a result of the particular species of plant [2].

In food products, the functional roles of starch could be as a thickener, binding agent, emulsifier, clouding agent or gelling agent. In the food industry, native starch is usually reprocessed and modified through chemical processes to improve its functionality for the desired purpose. Chemical modification involves the introduction of new functional groups into the starch molecule which produces in a modified starch with markedly altered physicochemical properties. Such modified starch shows profound change in functionality such as solubility, gelatinization, pasting and retrogradation [11].

The chemical reactivity of starch is dependent on the reactivity of the constituent glucose units [11]. The chemical and functional properties achieved following such modification depends largely on the reaction conditions such as modifying reagent(s), concentration of the reactants, reaction time, type of catalyst used, pH, and temperature. The type of substituents, degree of substitution and distribution of substituents in the starch molecule affects the functional properties.

Amylose

Amylose is a linear polymer of α-d-glucose units linked by α-1,4 glycosidic bonds (Figure 2). The linear nature of amylose chain and its percentage content in starch, and the relative molecular arrangement with amylopectin affect the overall functionality of the starch. Hence starch varies greatly in form and functionality between and within botanical species and even from the same plant cultivar grown under different conditions. This variability provides starches of different properties, which can create challenges of raw materials inconsistency during processing [12].

Amylopectin

Amylopectin is a branched polymer of α-d-glucose units linked by α-1,4 and α-1,6 glycosidic bonds (Figure 2). The α-1,6 glycosidic linkages occurs at the branching point while the linear portions within a branch are linked by α-1,4 glycosidic bonds. In comparison to amylose, amylopectin is a much larger molecule with a higher molecular weight and a heavily branched structure built from about 95% (α-1,4) and 5% (α-1,6) linkages. Amylopectin unit chains are relatively short with a broad distribution profile, compared to amylose molecules. They are typically, 18–25 units long on average [13, 14].

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3. Physicochemical properties of starch

Physical properties are those properties exhibited without any change in chemical characteristics of starch and do not involve the breaking and creation of chemical bonds such as solubility, gelatinization, retrogradation, glass transition, etc. On the other hand, chemical properties changes due to chemical reactions and usually involve the breakage and creation of new bonds. Examples of such chemical processes in starch include hydrolysis, oxidation, esterification and etherification. Research strongly indicates that the molecular weight and branching attributes of starch which play important roles in the shape and size of granules can potentially be used for predicting some of its functionality such as texture, pasting, retrogradation, etc. [12, 15]. Amylose has more proportional relationships with pasting and gel textural properties, while amylopectin which are predominant in regular and waxy corn starches, has higher proportional relationship with firmness.

Solubility and gelatinization

When unprocessed or native starch granules which are relatively inert are heated in the presence of adequate water, usually during industrial processes, swelling of the granules occur and the amylose dissolves and diffuses out of the swollen granules which upon cooling forms a homogenous gel phase of amylose-amylopectin. The swollen amylopectin-enriched granules aggregate into gel particles, generating a viscous solution. This two-phase structure, called starch paste, is desirable for many food applications where processed starches are used as thickeners or binders [2, 16].

Retrogradation and shear

Retrogradation of starch is a phenomenon that occurs when the disordered arrangement of the polymer molecules of gelatinized starch begins to re-align into an ordered structure in the food product [15]. Preventing retrogradation affects the freeze-thaw stability and textural characteristics and helps to elongate the shelf life of the food product. Starch modification through chemical means, such as, hydrolysis and esterification are generally used to produce starches that can withstand retrogradation. Preventing retrogradation of starch is important for starch used in frozen foods because it is accelerated at cold temperatures, producing an opaque, crystallized, coarse texture as a result of the separation of the liquid from the gel or syneresis [17, 18]. Crosslinked oxidized starches have been reported be more stable against retrogradation [15].

Amylose linear chain dissolves in water at –°C and is characterized by high thermostability, resistance to amylase, high crystallinity and high susceptibility to retrogradation. Amylopectin, which is the branched chain is however, slow to retrogradation, with crystalline forms appearing only on the outside of the globule and characterized by a significantly lower re-pasting temperature of 40–70°C and an increased susceptibility to amylases activity than amylose. Retrogradation of starch is affected botanical origin of the starch, amylose content, length of the amylopectin chains, density of the paste, paste storage conditions, physical or chemical modifications and the presence of other compounds. Recrystallization of starch applies only to amylose chains, and it occurs most readily at temperatures around 0°C, and also at temperatures above °C [8]. Physical modification process such as repeated freezing and thawing of the starch paste aggravate retrogradation. The resulting starch thus produced is resistant starch that exhibit resistance to digestibility by amylase enzymes and can be used as an alternative nutrient source for diabetic patients and as a rate controlling polymer coat in controlled drug delivery systems [8].

Starch granules swollen with water are predisposed to fragmentation if exposed to physical severe pressure change. This becomes of major concern where the integrity of the granules is required to maintain viscosity. Shear is the disintegration phenomenon of swollen starch granules or gel. Starch shear arises from the shear stress which builds up during the process of retrogradation and/or gel drying of the gelatinized starch [19]. The stress acting in opposite directions creates a fault-line that causes the material to open up or tear apart. Shearing generally depends on the fluid (gel) viscosity and flow velocity [20]. Starch granules in their raw unswollen forms are not susceptible to damage by shear even in the slurry before cooking. But once cooked or gelatinized, starch granules becomes susceptible to shear, resulting in loss of viscosity and textural stability [19].

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4. Chemical properties of starch

The chemical properties of starch are dependent on the reactivity of starch which is a function of the polyhydroxyl functional groups in the constituent glucose monomers. The hydroxyl groups at position C-2, C-3 and C-6 which are free from the glycosidic bond linkages and pyranose ring formation, are usually free for substitution reactions involving either the attached hydrogen or the entire hydroxyl group. While the &#;OH at C-6 is a primary alcoholic hydroxyl group, those at C-2 and C-3 are secondary alcoholic hydroxyl group. Hence starch can undergo hydrolytic cleavage of its chains at the glycosidic bonds; oxidative reaction with the &#;OH or C&#;C bond creating carbonyl groups; and other reactions with various functional and multifunctional reagents to produce esterified and etherified starches. Most of the reactions require activation of the hydroxyl of glucose units in acidic or basic media [7].

Reactions of starch

The reactivity of starch is dependent on the hydroxyl functions of the constituent α-D-glucan polymers (Figure 2). Thus starch is able to undergo the following reactions.

Hydrolysis

Hydrolysis is an addition reaction and simply involves the addition of a water molecule across a bond resulting in the cleavage of that bond and formation of the cleavage products, usually with hydroxyl group or alcohol functionality. Hydrolysis of starch can be achieved by chemical or enzymatic process. Chemical process of hydrolysis usually employs heating starch in the presence of water or dilute hydrochloric acid (Figure 3). Hydrolysis is also used to remove fatty substances associated with native starches. Hydrolysis under acidic condition is called roasting, resulting in acid modified starch. Treatment of starch with sodium or potassium hydroxide results in alkaline modified starch. Hot aqueous alkaline solutions can be used, and this improves the reducing value of that starch [21, 22, 23].

The products of starch hydrolysis include dextrin or maltodextrin, maltose and glucose. Dextrins are mixtures of polymers of d-glucose units linked by α-(1 → 4) or α-(1 → 6) glycosidic bonds. The percentage of products obtained depends on the conditions used for the reaction such as duration and strength/amount of reagents used. Enzymic hydrolysis uses the enzyme malto-amylase to achieve hydrolysis and this is the process that usually occurs in starch digestion in the gastrointestinal tract [9]. Dextrins are white, yellow, or brown water-soluble powder which yield optically active solutions of low viscosity. Most of them can be detected with iodine solution, giving a red coloration. White and yellow dextrins from starch roasted with little or no acid are called British gum. The properties of dextrinized starch is dependent upon the reaction conditions (moisture, temperature, pH, reaction time) and the products characteristics vary in its content of reducing sugar, cold water solubility, viscosity, color and stability.

Hydrolytic processes have been used in the food industry to produce starch derivatives with better functional properties and processing applications [2]. Acid and alkali steeping are the two most widely used methods for starch isolation in the food industry, with numerous modifications. Thermo-alkali isolation method known as nixtamalization has been used in Central America since pre-Hispanic times. Acid and alkali isolation processes affect the amylose/amylopectin, protein and lipid content as well as the granule size and shape of the final product [23].

Esterification reaction

The condensation of an alcohol and carboxylic acid usually under acidic condition, to produce an ester and water, is called esterification [24]. Basically, the reaction is between the carboxylic acid group and the alcohol group with the elimination of a water molecule (Figure 4). When the acid anhydride is used, an alkaline condition is preferred in the reaction.

The reaction is usually reversible and the forward reaction is favoured under low pH and excess of alcohol while the reverse is favoured under high pH. Remover of one of the product during the reaction will also favour the forward reaction.

For starch, the reaction is between the carboxylic acid group (&#;COOH) of fatty acids or &#;COCl of fatty acid chlorides and the alcohol group (&#;OH) of the glucose units. Esterification is generally used to introduce more lipophilic groups into the starch molecule making it more lipophilic and for producing crosslink starch when polyfunctional compounds or multifunctional or reagents capable of esterification or etherification are used [15]. Esterification weakens the inter-molecular bonding that holds the granules together and hence alter the granule shape and sizes as well as other functional properties of the starch. The degree of substitution (DS) is dependent on the concentration of reagent used, the type of reagent used, the catalyst and the duration of reaction [25].

Acetylation of starch

Starch can be acetylated by reacting it with acetic anhydride to produce acetylated starch (Figure 5). The hydroxyl group of the glucose units are esterified with the acetyl groups from the acetic anhydride to give starch with glucose units with acetate function. The DS of the hydroxyl group with acetate group is dependent on the reaction conditions. Acetylated corn starch of DS , and have been obtained using 4, 6 and 8% (starch d.w.) acetic anhydride respectively and aqueous sodium hydroxide as catalyst [25].

The introduction of the more bulky acetyl group compares with hydroxyl group causes steric hindrance to the alignment of the linear chains. This allows for easy water percolation between chains thus increasing the granule swelling power and solubility resulting in lower gelatinization temperature [25]. The steric hindrance of less polar acetyl group also reduces the amount of inter-molecular hydrogen bond formation, and weakens the granule structure, preventing molecular re-association and realignment required for retrogradation. However, depending on the DS and the interplay between the a weakened granular structure as result of interruption of the inter- and intra-molecular bonds, and reduced bonding with water molecules as a result of the hydrophobicity of the acetyl groups, the viscosity of the final product can be enhanced.

Acetylation improves paste clarity and freeze-thaw stability of starch. Starch acetates of low DS are commonly used in the food industry for quality consistency, and as texture and stability enhancers. The Food and Drug Administration (FDA) maximum DS of acetylated starches for food application is [19]. Starch acetate of high DS exhibit high degree of hydrophobicity and thermoplasticity and are soluble in organic solvents like chloroform and acetone, and are mostly used in non-food applications [25]. At DS, corn starch exhibit lower paste gelling, which is practically lost at DS. Most commercial starch acetates have < DS [19].

Acetylated distarch adipate, is a monosubstituted starch obtained by treating starch with acetic anhydride and adipic anhydride (Figure 6). It has been used since the s due to desire for improved stability of product in cold and freezing weather conditions. It is a good temperature change resistant agent used in foods as a bulking agent, stabilizer and thickener. It improves smoothness and sheen of soups and sauces [19]. The improved freeze-thaw stability of acetylated cross-linked waxy maize starch has led to its use in frozen sauces in vegetables, appetizers and pastries. Hydroxypropylation of cross-linked starch also dramatically improves the stability quality of puddings and frozen sauces [19].

Succinylation of starch

When starch granule is esterified with succinic anhydride, it produces succinyl starch, and the process is commonly referred to as succinylation of starch. Succinylation of starch was earlier achieved in the presence of aqueous pyridine and under reflux at °C (Figure 7). However, environmental concerns have led to the development of more green synthetic routes. Thus succinic ester of starch have been prepared by mixing starch with succinic anhydride solution in acetone and refluxing at °C for 4 h [25]. Sui et al. [26] was also able to induce a reaction by drop-wise addition of succinic anhydride to a water suspension of starch while maintaining pH at by drop-wise addition of sodium hydroxide.

Succinyl group weakens the inter-molecular bonding of starch polymeric chains in the granules, facilitating swelling, solubilisation and gelatinization at lower temperatures. Paste clarity is enhanced and retrogradation is reduced. However, there may be reduced stability against shear at high temperature and during cooling. Starch succinate is ionic and acts as polyelectrolytes. At low degree of substitution (DS), the succinate makes the starch more hydrophilic and viscos in solution [8, 25]. For its viscosity enhancing effect, succinylated starches could find application in production of non-gelling custard creams, and for its increased hydrophilicity, it could be used for enhancing the juicy/smooth taste of meat and fried products. Starch succinates can also be used in soups, snacks, and frozen/refrigerated food products as thickening or stabilizing agents.

Esterification of starch with octenylsuccinic anhydride (OSA) or octenylsuccinic acid in the presence of an alkali yields starch octenylsuccinate (Figure 8), while esterification with dodecyl succinic acid yield starch dodecyl succinate. The octenyl or dodecyl group introduce a reasonable level of lipophilicity to the product making it have dual functionality which can be used in emulsification and flavours encapsulation. OSA treated starches are used to stabilize oil-in-water food emulsions associated with beverage concentrates containing flavor and clouding oils [19]. It helps to protect emulsified and spray dried flavour oils against oxidation during storage. FDA allows a DS of

Commercial production of acetylated starch dodecyl succinate, di-substituted starch of low dodecyl succinate residue employs acetic anhydride reagent at alkaline pH [15]. An alkali-starch complex forms first, which then interacts with the carboxylic anhydride to form a starch ester with the elimination of carboxylate ion and one molecule of water [15]. Starch succinate offers freeze-thaw stability, high-thickening, low-gelatinization temperature, clarity of paste, good film-forming properties and resistance to retrogradation.

Phosphorylation reaction

Inorganic esters also exist, for instance, esters of phosphorous acid (H3PO3) and phosphoric acid (H3PO4). When starch granules are reacted with phosphorylating agents such as phosphoric acid, mono- or di-starch phosphate is formed (Figure 9). The resulting starch has increased stability at high and low temperatures, more resistant against acidic condition, and is applicable as a thickening agent. Orthophosphate and pyrophosphate has been used to achieve phosphorylation of starch under slightly acidic and high temperature conditions [27].

Phosphoryl trichloride (Figure 10), sodium tripolyphosphate (Figure 11) and sodium trimetaphosphate (Figure 12) have also been used under higher pH to obtain monostarch phosphate and di-starch phosphate [15, 28]. Phosphorylation reactions produce either monostarch phosphate or distarch phosphate which is a cross-linked derivative. However this depends on the reagents and reaction conditions. Usually, monoesters, rather than diesters, are produced with a higher degree of substitution [8]. Steric hindrance as a result of the introduced phosphate groups inhibits the linearity of amylose or the outer branch of the amylopectin chain where it reacted. This weakens the inter-molecular association and creates chains disaggregation, which leads to better paste clarity [8].

Distarch phosphate has the phosphate group esterified with two hydroxyl groups of two neighbouring starch polymer chains [29]. The phosphate bridge or cross-linking strengthens the mechanical structure of the starch granules. Phosphate cross-linked starches exhibit stability against high temperature, low pH and shear, and improved firmness of the swollen starch granule as well as improved viscosity and textural characteristic. Distarch phosphate is used as thickener and stabilizer and provides stability against gelling and retrogradation and high resistance to syneresis during storage [8].

In solution, several specie of the phosphate ion can exist and anyone may be responsible for the phosphorylation reaction depending on the reaction conditions. Phosphorylation has been demonstrated to mostly occur at the C-3 and C-6 of the glucose units, and the degree of phosphorylation depends on distribution of the chain length of the starch polymers [30]. Blennow et al. [31] also demonstrated that phosphate groups may play important role in the size distribution of the amylopectin side chains of phosphorylated starches. Some researchers have reported that about 60–70% of total phosphorus of starch monophosphate is located at C-6 while the rest is located at C-3 of anhydroglucose units. Most phosphate groups (88%) are on chain β of amylopectin [9].

Landerito and Wang [32] reported that phosphorylated starch prepared by the slurry treatment exhibited a lower gelatinization temperature, a higher peak viscosity, a lesser degree of retrogradation, and improved freeze-thaw stability compared with those prepared by the dry-mixing treatment. They believed that phosphorylation probably occurred in both amylose and amylopectin chains, and the amount and location of incorporated phosphate groups varied with starch types, which may be due to their different amylose and amylopectin contents. Waxy starch was more prone to phosphorylation, followed by common and high-amylose starches. Enzymic phosphorylation of starch has been reported [33]. Extrusion condition of °C, sodium tripolyphosphate concentration of ≥ g/ ml and pH have been used to obtain starch phosphate with high degree of substitution [34].

Etherification

Generally, alcohols (&#;OH) groups condenses with one another at high temperatures under acidic conditions to form ethers (Figure 13). The reaction mechanism is through a proton transfer from the catalyst to one of the molecule to form a cation, which loses the proton by extracting the &#;OH of the second molecule to form an ether and water.

Etherification of starch is usually done by use of epoxide reagents as depicted in Figures 14 and The epoxides are first reduced to diols through a nucleophilic ring opening of the epoxide (cleaving the C&#;O bond under aqueous, acidic or alcoholic condition) before the eventual condensation of one of the &#;OH group with that of starch [24]. Some etherification reactions occur under alkaline condition. Like esterification, etherification helps to mostly introduce lipophilic alkyl groups into the starch chains thereby reducing the hydrophilicity and the degree of inter- and intra-molecular hydrogen bonding [8].

Hydroxypropylation of starch

This reaction process produces hydroxypropylated starch (HPS), which is a starch ether produce by reaction of starch with propylene epoxide in the presence of an alkaline catalyst (Figure 14). HPS is used for enhancing stability and viscosity of food products. The hydroxypropyl groups introduced into the starch chains affect the inter- and intra-molecular hydrogen bonds, thereby allowing for more ease of displacement of starch chains in the amorphous regions [8]. HPS is more stable to prolonged high temperatures than starch acetate especially at pH 6, and has improves freeze-thaw stability. It is mostly used in refrigerated or frozen foods and in the dairy industry. The FDA allowable DS for HPS is [19].

Hydroxyethylation of starch

Hydroxyethylation of starch is performed by reacting starch with epoxyethane or ethylene oxide to produce the starch ether, hydroxyethylated starch (HES) (Figure 15). The health concerns of hydroxyethylated starch are limiting its use in the food industry. However they are mostly used in medicine and pharmaceuticals as plasma volume expander and extracorporeal perfusion fluids [35].

Carboxymethylation of starch

This is an etherification reaction process where starch is reacted with sodium chloroacetate or chloroacetic acid under certain conditions to produce carboxymethylated starch (CMS) (Figure 16). The reaction involves refluxing chloroacetic acetic acid with dry starch (anhydroglucose units) in the presence of sodium hydroxide in a solvent mixture of ethanol/isopropanol (ratio ). Anhydroglucose unit can be obtained from acid hydrolysed starch [36].

Cationization of starch

Another etherification reaction is cationization of starch in which starch react with electrophiles or electron-withdrawing reagents such as ammonium, amino, imino, sulfonium, or phosphonium groups to produce cationic starches (Figures 17–19), which are important industrial derivatives [15]. Cationic starches are usually prepared under alkaline conditions, and they exhibit higher dispersibility and solubility with better transparency and stability.

Cationic starches containing tertiary amino or quaternary ammonium groups are the most important commercial derivatives, however they are mostly used in the textile and paper industry.

For the production of sulfonium starch, halogenoalkyl sulfonium salts (e.g., 2-chloroethyl-methyl-ethyl sulfonium iodide or any β-halogenoalkyl sulfonium salt), vinyl sulfonium salts and the epoxy alkyl sulfonium can be used (Figure 19). Usually R1 is unsaturated group like alkylene, hydroxyalkylene, aralkylene, cycloalkylene, and phenylene group, while each of R2 and R3 can be alkyl, aryl, aralkyl, cycloalkyl and alkylene sulfonium groups and may also contain ether oxygen linkages and amino groups [37]. Factors such as reagent used and temperature, affect the reaction period which usually takes about 16–20 h.

Sulfonium starch display positive charge and can be used as thickeners in the form of aqueous dispersions or pastes. These dispersions are made by heating the suitable amount of sulfonium starch and water to a temperature of approximately 93°C. Upon cooling, the resulting dispersion becomes considerably clearer and more resistant to viscosity change compared to the untreated starch. Starch succinate and starch citrates which are obtained through esterification reactions have also been observed to exhibit high cationic properties [8].

Oxidation

Oxidation of starch with strong oxidizing agents mimics reaction of primary alcohols and diols. Primary alcohol &#;OH functions are oxidized (Figure 20) to its corresponding carbonyls (aldehydes and carboxylic acid), while vicinal diols (Figure 21) are cleaved by strong oxidants like periodic acid into its corresponding carbonyl compounds (aldehyde and/or ketones) [24]. Oxidation of secondary alcohol &#;OH produces ketones (Figure 22). Oxidation may result in breakage of some intra- and inter-molecular bonds and partial depolymerization of the starch chains [38].

Starches treated with oxidants fall into two broad classes: oxidized and bleached.

Oxidized starches are starches treated with oxidizing agents like sodium hypochlorite (NaOCl). The oxidizing agent can attack the glycosidic bonds hydrolysing them to alcohol (&#;OH) functions or/and C&#;C bonds of the glucose unit, oxidizing them to carbonyl functions of aldehydes, ketones and carboxylates (Figure 23). Higher pH favors formation of carboxylate groups over aldehydes and ketones. Some depolymerization usually occurs in the process. Introduction of carboxylate groups provides both steric hindrance and electrostatic repulsion. Oxidation is usually carried out on whole granules and it causes the granule to dissolve, rather than swell and thicken [19]. The reaction can introduce up to % of carboxyl groups in the granule [39]. Oxidation with chlorine or sodium hypochlorite reduces the tendency of amylose to associate or retrograde. The reaction rate of starch with hypochlorite is remarkably affected by pH, which tend to be higher at about pH 7 but becomes very slow at pH 10 [40]. Oxidized starches are used where intermediate viscosity and soft gels are desired, and where the instability of acid-converted starches is unacceptable [41]. Hence, pastes of oxidized starches have a lower tendency to gel compared to those of thin-boiling (or acid hydrolized) starches of comparable viscosity.

Other oxidants such as chlorine, hydrogen peroxide and potassium permanganate, dichromates and chlorochromates, etc. are less commonly used. Oxidized starches are reported to give batters improved adhesion to meat products and are widely used in dough and baked foods [41].

Bleached starch is obtained from oxidation of starch with lower concentrations of oxidizing agents like hydrogen peroxide, sodium hypochlorite, potassium permanganate or other oxidants used to remove color from naturally occurring pigments. Bleaching is done to improve the whiteness and/or eliminate microbial contamination. Reagent levels of about % are usually used, and loss of some starch viscosity due to hydrolysis usually occurs.

Cross-linking of starch

Cross-linking of the starch polymer chains with reagents that could form bonds with more than one hydroxyl group of molecule results in cross-linked starch. Such reactions randomly add inter- and intra-molecular bonds at different locations in the starch granule which helps to strengthen and stabilize the polymers in the granule. Such processes may employ hydrolysis, oxidation, esterification, etherification, phosphorylation or combinations of these methods in a sequential or one-mix procedure to achieve the desired product that meets the required physicochemical characteristic of gelatinization, viscosity, retrogradation, and textural properties for food applications. In some instances, multifunctional reagents capable of forming either ether or ester inter-molecular linkages between hydroxyl groups on starch molecules are used. Reactions usually take place at the primary &#;OH group of C-6 and secondary &#;OH of C-2 and C-3 of the glucose units. Epichlorohydrin monosodium phosphate, phosphoryl trichloride, sodium trimetaphosphate, sodium tripolyphosphate, a mixture of adipic and acetic anhydride, and vinyl chloride are the main agents used to cross-link food grade starches [15]. Di-starch phosphate (Figure 12) which is a phosphorylated starch is an example of a crosslinked starch. Acetylated distarch adipate (Figure 6), hydroxypropyl distarch phosphate, hydroxypropyl distarch glycerol are other examples of crosslinked starch [8]. The FDA specify that not more than , 1 and % DS (w/w of starch) of phosphoryl chloride, sodium trimetaphosphate and adipic-acetic mixed anhydride, respectively, should be used for food grade starch [19].

Cross-linked starch exhibit increased resistance to processing conditions such as high or low temperatures and pH. Cross-linking reduces granule rupture, loss of viscosity and the formation of a stringy paste during cooking, providing a starch suitable for canned foods and products. Cross-linked starch shows smaller swelling volume, lower solubility and lower transmittance than native starch [15]. While oxidation may increase retrogradation, crosslinking reduces it. Hence a combination of the two chemical modification methods can be used to get the starch with desired balanced characteristics.

Approaches to modification of starch

As mentioned in the introductory section, native starches are modified to improve their physicochemical properties due to different reasons. Different approaches have been reported including physical, chemical, enzymatic and genetic approach. But the most widely used is the chemical approach. For instance, since starch must be gelatinized for it to be digestible in human diet and nutrition, and the process of gelatinizing native starches usually takes appreciable amount of time for granule to swell and form paste of gel as obtained in cooking rice and corn flour porridge, it can be modified to reduce gelatinization time by physical methods such as extrusion, spray-drier and drum dryer, which promote fast starch gelatinization to produce pregelatinized starch [42, 43, 44]. Pre-gelatinized starch exhibit reduced gelatinization temperature and time. The modified starches are usually dries to obtain flours and/or pre-gelatinized starches of long-term stability and quick preparation [9]. Pregelatinized starches are partially or totally soluble in cold water and readily form pastes [45]. It absorbs more water and disperses readily in water than the untreated starch, forming gel at room temperature and less prone to deposit [46]. Using gelatinized starch in food products affects the food qualities and properties, such as, bread volume and crumb [47]; pastas elasticity and softness, lusciousness and digestibility, tolerance in the properties of beating and cake mixtures, ice creams, doughnuts, growth of sugar crystals in food products [48]; texture, volume, shelf-live and stability during thawing of cakes and breads [49]. Liquefaction, partial hydrolysis and dextrinization may occur during pregelatinization depending on the processing conditions [42, 43, 44].

The process of physical modification does not involved any chemical reaction of starch with a modifying reagent and is referred to as physical modification of starch and the products are known as physically modified starches. However, most modifications of starches are performed through chemical processes. The chemical reactions of starch (hydrolysis, esterification, etherification, oxidation and cationization) are generally exploited in the industry to produce converted or modified starches fit for different purposes in the industry.

According to the Food and Nutrition Program (FNP) of the FAO [50], a modified starch is a food starch which has one or more of its original physicochemical characteristics altered by treatment in accordance with good manufacturing practice by one of the reaction procedures such as hydrolysis, esterification, etherification, oxidation and cross-linking. For starches subjected to heating in the presence of acid or with alkali, the alteration (mainly hydrolysis) is considered a minor fragmentation. Bleaching is also essentially a process resulting in the colour change only. However, oxidation involves the deliberate creation of carboxyl groups. Treatment of starch with substituting reagents such as orthophosphoric acid etc., results in partial substitution in the 2-, 3- or 6-position of the anhydroglucose unit (AGU) unless the 6-position is occupied for branching in amylopectin chain. For cross-linked starch, where polyfunctional substituting agent, such as phosphorus oxychloride, connects two chains, the structure can be represented by Starch&#;O&#;R&#;O&#;Starch, where R is the cross-linking group and Starch refers to the linear and/or branched structure [50].

Evolving biotechnological innovations are progressing with enzymatic and genetic modification of starch as a greener alternative to chemical modification due to environmental concerns. Enzymatic modifications basically employ hydrolytic enzymes found in certain bacteria. For instance amylomaltases or α-1,4-α-1,4-glucosyl transferases from and cyclomaltodextrinase (CDase 1–5) from alkalophilic sp. [48]. While α-1,4-α-1,4-glucosyl transferases breaks existing α-1,4 bonds and make new ones to produce modified starch used in foods and non-foods applications, CDase 1–5 can be used to produce starches which are low in amylose content without changing the amylopectin distribution. The granule of starch-cyclomaltodextrin complex produced special tastes and flavours, as well as light, heat and oxygen-sensitivity stability. Transglucosidase, maltogenic α-amylase and β-amylase have been used to produce resistant starches of various degrees of digestibility [8, 51, 52]. On the other hand, genetic modification employs biotechnology to targets the starch biosynthetic process. Genetic regulation of enzymes such as starch synthetase and branching enzymes, involved in starch synthesis through starch synthase genes are used to produces cereal crops that yield amylose- free starch, high-amylose starch and altered amylopectin structure in starch [8].

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5. Starch functionality and its applications in food

The reactions of starch explained above are exploited to create different types of modified or converted starched to obtain starches with appropriate physicochemical characteristics such as gelatinization, retrogradation, heat stability, solubility, transmittance, colour, texture, etc., for different industrial applications. The food industry is very mindful of safety of chemical residues hence not all types of modified starched are used in foods. Generally, modified starches are used for adhesion and as binder in battered and breaded foods, formed meat and snack seasonings; as dustings for chewing gum and products produced in the bakery; as crisping cover for fried snacks; fat replacer and juiciness enhancement in ice cream and salad dressings; flavour encapsulating agents in beverage clouds; emulsion stabilizers in beverages, creamers and canned foods; foam stabilizer in marshmallows; gelling agents in gum drops and jelly gum; and as expanders in baked snacks and cereal meals [19]. Table 1 gives a summary of the chemical modification processes and their food application.

Chemical processSpecific treatmentProductsFunctionFood applicationReferences
HydrolysisAcid treatmentAcid-hydrolized starch, acid thinned or thin-boiling and fluidity starchesReduced hot-paste viscosity, improved gelling or gel strength. Enhanced textural propertiesGum, pastilles, jellies[19]
Acid treatmentDextrinized starchIncreased solubility and gel stability, reduced viscosity and improved emulsification properties. Encapsulate volatiles aromatic compound such as limonene, isoamyl acetate, ethyl hexanoate and β-iononesFat replacer in bakery and dairy products, bakery glazes, protective coating in confectionery. Flavour encapsulator in seasonings[1, 19]
NaOH or KOH treatmentAlkaline hydrolysed starchIncrease viscosity[22]
OxidationSodium hypochlorite oxidized starchOxidized starchLower viscosity, improved whitening of granules, high paste clarity, low temperature stability, and increased adhesion. Reduces retrogradation of cooked starch pastesAs binder in battered meat and breading, film former and binder in confectionery, crispy coating in various fried food stuffs, texturizer in dairy products[15]
EsterificationMonosubstituted starch (starch acetates, starch hydroxypropyl ethers, starch monophosphate esters)Freeze-thaw stability, improved emulsification propertiesAs emulsion stabilizers and for flavor encapsulation in refrigerated and frozen foods[15, 19]
Acetylation with acetic acid anhydrideStarch acetateIncreased lipophilicity emulsion stabilizer. Improves quality of any fat/oil-containing products. Reduces rancidity by preventing oxidation. Increase viscosityBulking agent in snack foods, stabilizer and thickener in most foods, improves smoothness and sheen of soups and sauces. Cholesterol-free salad dressings, and flavor encapsulating agents in clouding agents, creamer and beverage. Substitute to gum arabic, egg yolk and caseinates[1, 15, 19]
Succinylation with succinic acid anhydrideStarch succinateImproved viscosity and juice taste. Freeze-thaw stabilitySoups, snacks, and frozen/refrigerated food products. As thickener and in non-gelling custard creams. Meat and fried products to improve juicy or smooth taste and retain flavour[25]
Succinylation with OSAOSA starchIncreased paste viscosity, emulsion stabilizer and lower gelatinization temperature. Reduces glycemic response after consumption of beveragesBeverage emulsion stabilizers, and mayonnaises. Flavour encapsulating agent for battered meat and meat products[19, 25, 53, 54]
Treatment with adipic anhydrideStarch adipateHigher paste viscosity, clarity and stabilityThickening agent in foods[25]
PhosphorylationStarch phosphateBetter paste clarity, lower gelatinization temperature, higher viscosity, reduced retrogradation, and improved freeze-thaw stabilityFrozen foods[8]
Distarch phosphateStability against high temperature, low pH and shear, and improved firmness of the swollen starch granule as well as improved viscosity and textural characteristic, resistance to syneresis during storageAs a thickener and stabilizer in foods such as soups and sauces[8]
EtherificationEtherified starchesImproved clarity of starch paste, greater viscosity, reduced syneresis and freeze-thaw stabilityAs stabilizer in wide range of food applications such as gravies, dips, sauces, fruit pie fillings and puddings. Flavour encapsulating agent in beverages clouds[15]
CarboxymethylationCMSCold-water solubilityCandy foods, sweets[1]
HydroxypropylationHPSImproves freeze-thaw stability, water-holding properties, lowers the swelling/pasting temperature, increases paste clarity and reduces gel formation. More stable to prolong high temperatures. Increase solubilitySalad dressing, ice creams, refrigerated and frozen foods, and dairy products[19]
CationizationSulfonium starchHigher dispersibility and solubility with better paste clarity and stability[19]
CrosslinkingCrosslinked starchesHigher stability to granules swelling, high temperature, high shear and low pH. Better viscosity and freeze-thaw stability. Volume expander. Delays retrogradation and reduce paste clarityAs thickener and texturizers in soups, sauces, gravies, bakery and dairy products. Filling in fruit pies and canned foods. In bread and dough products as expander and to improve rheological properties[9, 15, 53, 55]
Crosslinked-hydroxypropylated starchA smooth, viscous, clear thickener and freeze-thaw stabilityGravies, dips, sauces, fruit fillings and puddings[15]
Pre-gelatinized starchCold-water solubility and thickeningInstant soups, sauces, dressing, desserts and bakery mixes. Thickener in food that receive minimal heat processing such as pastas[15, 19]

Table 1.

Application of chemically modification starches in foods.

Baked products (bread, pies, samosas, wafers, biscuits and sausages)

Baked products like biscuits, pies, bread, cakes wafers and sausages are high density products requiring heat resistant starches. Hence crosslinked starches are used since they are more resistant to oven baking temperatures of ≥ °C. Gelatinized starches are also used in ready-to-eat cereal meals such as corn-flakes, etc. The temperature, humidity and degree of stirring determine the texture and quality of the product.

Confectionery (candy, sweets and sweetmeat)

Oxidized starches have high clarity or transmittance, low viscosity and low temperature stability. It is frequently used in confectioneries for coating candies and sweets since they easily melt.

Gravies, soups and sauces (soups, sauces, tomato paste or ketchup)

Etherified and crosslinked starches are mostly used. Crosslinked starched have higher stability for granules-swelling, high temperature resistant, high shear stability and acidic conditions stability. They are used as viscosifiers and texturizers in soups, sauces, gravies, bakery and dairy products. Etherified starches have improved clarity of starch paste, greater viscosity, reduced syneresis and freeze-thaw stability. Crosslinked starches are used in wide range of food applications such as gravies, dips, sauces, fruit pie fillings and puddings.

Mayonnaises, salad dressing, ice cream, spreads and beverages

Hydrolyzed and esterified starches are mostly used in salad dressing and beverages. Hydrolyzed starch (acid-modified starches) has lower paste viscosity under cold and hot conditions. Hence they are used in mayonnaises and salad dressing [19]. Esterified starches have lower gelatinization temperature and retrogradation, lower tendency to form gels and higher paste clarity, and are used in refrigerated and frozen foods, as emulsion stabilizers and for encapsulation of beverage clouds. OSA starch is used as emulsifiers in mayonnaises and salad dressings.

Pasta (spaghettis, macaroni, others)

Pregelatinized and crosslinked starches are mostly used in pastas. Gelatinized starch affects pastas elasticity and softness, delectableness and digestibility. Crosslinking gives the needed structural firmness to the pasta.

Puddings (custard, pap, others)

Pregelatinized starches are used in puddings, instant lactic mixtures and breakfast foods to achieve thickening or water retention without employing heat. They are also used in ready-to-use bread mixtures. They are used where little or no heat is required and the increased absorption and retention of water improves the quality of the product; as an agglutinant in the meat industry; and as a filling for fruit pies [9, 49].

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6. Conclusion

The importance of starch as a biopolymer continues to be on the upward trend due to its versatility. It has transformed from its traditional use as energy-source food to more sophisticated food and non-food applications. Its growing relevance in modern technological application is as a result of its susceptibility to modification, which transforms the native properties into more desirable and malleable characteristics fit for different purposes. These modifications are only possible due to the chemical reactivity of the constituent glucose monomers of the starch chains. Though the starch granule is inherently almost unreactive, it is however easily activated for reaction by certain conditions such as high or low pH, higher temperature, presence of a catalyst, etc. Under the right condition, starch molecules can undergo hydrolysis, oxidation, esterification and etherification reactions to produced products of improved organoleptic, textural, mechanical and thermoplastic properties of desirable foods and non-foods application. Modified starches like starch acetate, starch phosphate, HPS, CMS, sulfonium starches and their crosslinked derivatives are used for various applications in the food industry. However, concerns for chemical residues in these products and environmental considerations for hazardous chemicals used in some of the process, have led to more studies for greener modification processes. Though biotechnology has evolved enzymic and genetic modification processes for production of some modified starches, they are still highly limited and sometimes uneconomical, hence chemical modification remains the most versatile and mostly used.

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Conflict of interest

The author declares no conflict of interest.

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Henry Omoregie Egharevba (August 5th ). Chemical Properties of Starch and Its Application in the Food Industry, Chemical Properties of Starch, Martins Emeje, IntechOpen, DOI: /intechopen Available from:

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Physicochemical, structural and functional properties of native and irradiated starch: a review

Impact on the functional properties

The starch digestibility varies according to the source and this varying property of its digestibility has found a great importance for developing the foods for diabetic persons. The variations in the digestibility of starch is ascribed to its source, chemical structure and composition. There have a lot of research suggesting that the in vitro digestibility of the starch can be increased by irradiation (Bravo et al. ; Rombo et al. ). Some of the studies pertaining to the starch digestibility as affected by the gamma irradiation are discussed hereunder.

Kume et al. () demonstrated that the gamma irradiated corn starch enhanced the digestion besides decreasing the cooking temperature. The viscosities of porridges made from gamma irradiated maize, beans and their composite flours decreased with increase in dosage level (0, , 5, and 10 kGy) (Rombo et al. ). They also found that starch digestibility was higher at dosage of  kGy in case of maize, with subsequent increase in the dosage level the starch digestibility was reduced. The digestibility of the maize was found higher as compared to the bean starch for the same treatments. The effects of the gamma irradiation (0, 5, 10, 20 and 40 kGy) on the polysaccharides of bean and maize flours were studied by Rombo et al. (). They employed the techniques like NMR, polarized light microscopy, DSC and X-ray diffraction for investigating the effects of irradiation treatment. They concluded that the beta bonded starch content was increased with irradiation dose which is responsible for the reduced starch digestibility. The degradation of amylopectin was also observed. Degradation of amylopectin and formation of beta bonded starch increased the crystallinity.

Chung and Liu () demonstrated that the gamma irradiation decreased the RDS content when subjected to 10 kGy while at 50 kGy the RDS content was increased. While the RS content decreased up to 2 kGy but showed an increasing trend afterwards up to 50 kGy. They also reported that the swellability and carboxyl content reduced with slower irradiation doses.

The in vitro digestibility of the corn starch treated with gamma irradiation (5, 10, 15 and 20 kGy) was studied by Yoon et al. (). They found that the average molecular weight of the starches was decreased but the fractions of rapidly digestible and resistant starch was increased. Waxy starch was found more sensitive towards irradiation as compared to normal corn starch. They concluded that the increase in the resistant starch content indicates that the starch has undergone structural modification and chain degradation as well. Chung et al. () studied the in vitro digestibility and pasting characteristics of the gamma irradiated (10, 20, 40 and  kGy) starches obtained from the waxy maize. They demonstrated that RS content was decreased by about 20% when compared to the initial values. However, the RDS was increased significantly. They also concluded that the alpha amylase activity was higher from inside as compared to the outside granule.

Other studies

Nowadays, due to the increased concerns regarding the environmental pollution the use of plastic materials has been avoided and the development of the alternative packaging materials has gained interest having the properties of eco-friendly, non-pollutant and biodegradable. Starch has been studied extensively to develop starch based polymeric packaging materials. Although, the mechanical properties are less as compared to the plastics. But the advancement in newer technologies like gamma irradiation has minimized these limitations. Zhai et al. () studied the effects of gamma irradiation and electron beam irradiation (0, 10, 30, 50, 70, 90, and  kGy) on the starch and polyvinyl alcohol blended hydrogels. They found that the irradiation resulted in the cross linking between starch and polyvinyl alcohol. Jo et al. () used gamma irradiation (0, 10, 20, and 30 kGy) for the development of biodegradable film. The raw materials selected were pectin and gelatine. They found that the irradiation dose of 10 kGy produced film with highest tensile strength. Al-Assaf et al. () used gamma irradiation for the controlled modification of the film structure of Acacia Senegal (gum arabic). They also used acetylene as a mediating gas for the systematic modification. They initially used a dosage of  kGy which was then compared to the higher doses of and  kGy. The higher doses resulted in the formation of hydrogels. They concluded that irradiation could be used for the development of films with desired characteristics. Kim et al. () studied the impact of gamma irradiation on the development of corn starch based film using locust bean gum (0%, %, and %, w/v), sucrose, polyvinyl alcohol, and glycerol. The samples were irradiated at doses of 0, 3, 6, 12, and 24 kGy. The results revealed in the development of smooth, intact and yellowish coloured film. The results showed that the tensile strength of a % (w/v) locust bean gum when irradiated with 3 kGy resulted in 85% more elongation when compared to non-irradiated samples. The addition of % locust bean gum along with irradiation at 6 kGy for a starch-based film was estimated to be the optimum value. They concluded that irradiation could be an important tool for enhancing the mechanical properties of starch based films.

Sours: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC/
Physical vs Chemical Properties - Explained

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Properties starch chemical

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Starch : introduction, structure \u0026 properties - B.Sc 5th sem

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Now discussing:

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