STARCH & MODIFIED STARCH

STARCH• Also known as amylum, • major carbohydrate storage material in many higher plants;

the second largest natural biopolymer next to cellulose. • It is the basic source of energy and plays a major part in

supplying the metabolic

• Most starches are composed of:1. a linear fraction, amylose (15-25%) and 2. a highly branched fraction, amylopectin.

• The ratio of amylose and amylopectin in starch varies from one starch to another.

• The two polysaccharides are homoglucans with only two types of chain linkages, an a-(14) of the main chain and a-(16) of the branch chains.

amylose• a linear macromolecule consisting of a-glucopyranose residues linked together by a-

(1→4) bonds; 200-2000 units• Each macromolecule bears one reducing end and one nonreducing end. • may has a few phosphate groups, probably at the C-6 position of glucose residuesPhysicochemical properties• The abundance of hydroxyl groups along the amylose molecules imparts hydrophilic

properties to the polymer, giving it an affinity for moisture & dispersibility in water• Because of their linear nature, mobility, and the presence of many hydroxyl groups along

the polymer chains have a tendency to orient in a parallel and approach each other closely enough to permit hydrogen bonding between adjacent chains.

• As a result, the affinity of the polymer for water is reduced and the solution becomes opaque.

amylopectin• Amylopectin is a highly branched polysaccharide. The structure consists of a-D-

glucopyranose residues linked mainly by a-(1→4)-linkages (as in amylose) but with a greater proportion of nonrandom a-(1→6)-linkages, which gives a highly branched structure (every 15-25 units)

• Amylopectin is one of the largest biological molecules and its molecular weight (Mw) ranges from 106 -109 g/mol

Physicochemical proper• The large size and the branched nature of amylopectin reduce its mobility in

solution and eliminate the possibility of significant levels of interchain hydrogen bonding.

• Each amylopectin molecule contains a million or so residues, about 5% of which form the branch points.

• There are usually slightly more 'outer' unbranched chains (called A-chains) than 'inner' branched chains (called B-chains). There is only one chain (called the C-chain) containing the single reducing group.

• Starch exists in the form of granules (i.e an immense and highly organized structure);

• A pound of corn starch contains about 750 billion granules

• composed essentially of homopolymer of a-D glucopyranosyl units and small amounts of noncarbohydrate components, particularly lipids, proteins, and phosphorus.

• Starch granules consist of amorphous/non crystalline and crystalline regions

• The areas of branching points are believed to be amorphous the main swellable structure of native starch

• The presence of amylose tends to reduce the crystallinity of the amylopectin and influence the ease of water penetration into the granules

• The crystalline regions or the crystallites are formed from the short branch chains of amylopectin molecules which is strong bond, numerous and strong

• The presence of a-(1→6)- bonds in amylopectin is responsible for the alternation between amorphous and crystalline zones;

• In this hydrogen bonding is weaker

Gelatinization• Native starch granules are insoluble in cold water but swell in warm water. When

starch granules are heated in the presence of water, an order-to disorder phase transition occurs.

• Starch gelatinization is the collapse (disruption) of molecular orderliness within the starch granule along with concomitant and irreversible changes in properties such as granular swelling, crystallite melting, viscosity development, and Solubilization.

• there are two distinct mechanisms by which ordered regions of starch undergo phase transition over a wide range of moisture contents:

1) The low temperature endotherm reflects stripping and disorganization of polymer chains from crystallites — processes that are facilitated by the swelling action of water on the amorphous regions.

2) As the water content decreases and becomes insufficient for the above process of complete melting, the partially hydrated crystallites tend to melt at a higher temperature whose value depends on the volume fraction of the diluent (water),

• The abundant of hydroxyl group primary factor in absorbing water• When a slurry of starch in water is heated > Tc hydrogen bonds holding the

granules is weaken, permitting to swell GELATINIZATION• As the swelling occur, viscosity increase• Some of the molecule leach out swollen granules, eventually reach max hydration

then begin to rapture and collapse

Gelatinization stages• Gelatinization on a macroscopic scale

causes thickening and loss of opacity• Gelatinization stages:(a). raw starch granules made up of

amylose (linear) and amylopectin (branched) molecules .

(b). the addition of water breaks up crystallinity and disrupts helices

(c). Addition of heat and more water causes granules to swell and amylose diffuses out of the granule

(d). Granules, mostly containing amylopectin are collapsed and held in a matrix of amylose

Pasting• following gelatinization in the dissolution of

starch; • When starch is cooked, the flow behavior of a

granule slurry changes markedly as the suspension becomes a dispersion of swollen granules, partially disintegrated granules, then molecularly dispersed granules. The cooked product is called a starch paste

• In general, a starch paste can be described as a two-phase system: a dispersed phase of swollen granules and a continuous phase of leached amylose

• It can be regarded as a polymer composite in which swollen granules are embedded in and reinforce a continuous matrix of entangled amylose molecules

• When heated in water, the starch granule begins to swell as thermal energy breaks hydrogen bonds between adjoining starch polymers.

• Amylose starts in amorphous regions are solubilized first. Water diffuses first into the center of the granules and the degree of leaching of amylose out of the granules is low.

• Bonds in the crystalline areas hold the granule intact until a point is reached where they are also broken. With continued heating, the granule swells to many times its original volume.

• If there is lipid in the system, amylose-lipid complexes are believed to restrain swelling and amylose leaching. Once the amylose-lipid complexes dissolve, the rate of amylose leaching out of the granules increases substantially.

• When the temperature increases, the amylopectin-rich granules swell tangentially. The granule deforms and loses its original shape.

• The presence of amylose in the continuous phase surrounding the swollen granules will result in the formation of a strong gel on cooling

Retrogradation• physical behavior changes following gelatinization• defined as the linking of starch chain into ordered crystalline structure• Linear fraction of starch is particularly susceptible to retrogradation, AM is slower• occurs when starch molecules reassociate and form an ordered structure during

cooling• Takes in two stages:(1) fastest stage formation of crystalline regions from retrograded amylose. (2) The second stage involves the formation of an ordered structure within

amylopectin• During the retrogradation, the molecular interactions (mainly hydrogen bonding

between starch chains) occur removed water• Amylose is able to form double helical association of 40 to 70 glucose units,

whereas amylopectin crystallization occurs by association of the outermost short branches (e.g., DP = 15)

Starch typesStarches have been classified into four types based on their gelatinized paste

viscosity profiles:• Type I is the group of high swelling starches (e.g., potato, tapioca, waxy

cereal), which are characterized by a high peak viscosity followed by rapid thinning during cooking.

• Type II is moderately swelling starch, which shows a lower peak viscosity, and much less thinning during cooking (e.g., normal cereal starches).

• Type III consists of restricted swelling starches (e.g., chemically cross-linked starches), which show a relatively less pronounced peak viscosity and exhibit high viscosity that remains constant or increases during cooking.

• Type IV is highly restricted starch (e.g., high amylose maize starch), which does not swell sufficiently to give a viscous solution.

Digestion process• Digestion of starch consists of breaking up the glycosidic bonds by glycosidases

in order to liberate glucose• When food that has been thoroughly chewed reaches the stomach, acidity

inactivates the salivary a-amylase, but by then the large starch molecules have been reduced from several thousand to a few glucose units.

• As the stomach empties, the hydrochloric acid in the material entering the small intestine is neutralized by secretions from the pancreatic ducts, bile, and pancreatic juices

• The digestibility of starch is very much dependent on the intactness of tissue structures, the degree of swelling of starch granules, and the amount of retrograded amylose outside the starch granules.

• It is possible to manipulate the digestibility of starch in food by the use of appropriate processing techniques, such as preservation of the cell wall structure of plant foods, or introduction of a secondary structure that will hinder access of amylase.

• milling, may damage the plant cell structure and starch may be completely gelatinized rapid digestion of starch in the small intestine

• The digestion of starch dextrins is continued by the action of pancreatic a-amylase. The products of digestion by a-amylase are mainly maltose and maltotriose, and a-limit dextrins containing about eight glucose units with one or more a-1→6 glucosidic bonds.

• Finally hydrolysis of di- and oligosaccharides is carried out by surface enzymes of the small intestinal epithelial cells.

• Di-, oligo-, and polysaccharides that are not hydrolyzed by a-amylase and/or intestinal surface enzymes cannot be absorbed, and they reach the lower tract of the intestine, which from the lower ileum onward, contain bacteria.

Resistant starch• Most starches, native or modified, contain varying proportions of rapidly digesting,

slowly digesting, and resistant • Rapidly digestible starch is starch that is rapidly and completely digested in the small

intestine;• slowly digestible starch (SDS) refers to starch material that is hydrolyzed to glucose,

but at a moderated or reduced rate, during its transit through the human small intestine.

• Although it is eventually absorbed as glucose within the small intestine, hydrolysis and absorption of SDS occur over a more extended period (relative to rapidly digestible starch), thus providing a moderating effect on blood sugar levels.

• Resistant starch (RS) is defined as starch material that escapes digestion by human enzymes within the small intestine and passes into the colon, where it is metabolized into secondary products by colon microflora.

• Resistant starches result from the formation of glycosidic bonds, other than the a–(1–4) or a–(1–6) links by treatments involving heating, cross-linking, hydroxypropylation, or phosphatation, which can reduce the digestibility of the starch.

Resistant starch typeFour main types: • type I physically entrapped/inaccessible starch, which is protected by the wall cel

(e.g., in partly milled grains and seeds). The presence of intact cell walls contributes to the resistant Starch content of legumes. More extensive milling and chewing can make these starches more accessible and less resistant. represented by the inaccessible starch

• Type II ungelatinized (raw) starch or starch granules whose degree of crystallinity has been increased (e.g., the native crystalline starch granules in raw potatoes, green bananas, and high amylose corns).

• Type III the starch fraction not digested, formed by hydrothermal treatments that cause retrogradation/retrograded starch.

• Type IV chemically modified starches that are used by food manufacturers to improve the functional characteristics of the starch.

• However, overlap of RS categories or types within a single RS product, as multiple approaches are often found since utilized simultaneous treatments applied to achieve the overall resistance to digestion

MODIFIED STARCH• The amylogram in Figure I depicts the

rapid hydration of unmodified waxy granules accompanied by a sharp increase in viscosity (A).

• With continued cooking, the granules rupture, leading to a very rapid decrease in viscosity (B).

• As can be seen, there is a narrow range at which waxy corn develops and loses its viscosity (C).

• These rapid changes in viscosity are accelerated by heat, acid and shear.

• This narrow viscosity range along with the starch’s susceptibility to processing conditions would make manufacture of an acceptable product virtually impossible.

• Native starches have many disadvantages for industrial applications e.g. insolubility in cold water, loss of viscosity, thickening power after cooking, low shear stress resistance and thermal decomposition, poor processability and solubility in organic solvent

• MS is aimed at correcting properties which will enhance its versatility and satisfy consumen demand

• by means of altering the structure and affecting the H bonding in controllable manner to enhance & extend the application

• The functionality of starch can be modified through physical, chemical, and biotechnological means.

• Starch can be physically modified by mechanical, T, P, shear, MC, & irradiation treatment

• Starch is widely modified by chemical methods. The most common chemical modification processes are acid treatment, cross-linking, oxidation, and substitution, including esterification and etherification.

• Biotechnology modified cell, enzyme

Physical modification

• Physical modification of starch can be applied alone or with chemical reactions

• Objectives to change the granular structure and convert native starch into cold water soluble starch or into small crystallite starch.

• More preference as this do not involve chemicals• Including pregelatinization, particle size adjustment and

moisture adjustmen

pregelatinization• Certain starches require cooking to develop their

function by simultaneously cooking and drying (drum drying & spray drying)

• Because of pregelatinization and drying, the granular integrity is lost and paste viscosity of starch is reduced. Therefore, the modified starch is cold water soluble.

• rearrangement of inter and intramolecular hydrogen bonding between water & starch molecule resulting in collapse/discruption of molecular orders within the starch granule

• Effects instantly hydrates and swells in water at room temperature; the particles swell upon rehydration, but do not disperse under heat and shear

• The modification is irreversible changes in starch properties but tend to retain some of the physicochemical properties of the starting base material.

• if the pregelatinization step is done properly, most of the heat, acid, and shear stability of a crosslinked starch is retained.

• However, finely ground products of pregelatinized starches are difficult to disperse in water homogeneously since they hydrate rapidly at contact with water and form lumps.

• Pregelatinized starch is used as a thickening agent in foods that receive minimal heat processing.

• Applied to products with viscosity without the need for cooking or high temperatures, which means that the food manufacturer does not need to precook the starch.

• Such techniques include pregelatinization of starch for quick viscosity development in instant systems, cold water swelling starches for instant systems where more process tolerant products are needed such as in microwaves, and adjustment of particle size to control dispersability and hydration

• E.g pie fillings, puddings, sauces, and baby foods.

HEAT-TREATED STARCH• Under controlled conditions, granular starch can be heat treated and

recovered in its granular form result in starch which maintained cook-up properties, but it shows improved viscosity and stability when subsequently gelatinized and pasted.

• Although heat-treatment processes are not mainstream, they are unique in that chemical reagents are not required to impart a modifying effect. The resultant starch may be considered native and therefore labeled “food starch.”

• There are two types of heat-treatment processes: heat-moisture and annealing

• Both of which cause a physical modification of starch without any gelatinization or damage to granular integrity

• Heat-moisture and annealing treatments induce the rapid migration or rearrangement of the amylose molecules in the granules to form intermolecular bonds between the amylose molecules and/or between the amylose molecules and the amylopectin molecules.

Heat moisture treatment• The heat-moisture treatment involves heating

starch at a temperature above its gelatinization point but with insufficient moisture to cause gelatinization (<35 C)

• heat-moisture treatment reduced the paste consistency and swelling power; increase thermal stability, gelatinization temperature, susceptibility towards a-amylase and acid hydrolysis; broadens the gelatinization temperature range.

• This reduction could be caused by: 1)chain-cleavage, 2) interaction between starch chain, 3) arrangement of amylose chains within amorphous domain, 4) amylose-lipid complexing, or 5) amylose-amylose association during heat-moisture treatment

annealing• modifies the physicochemical properties of starch without destroying the

granule structure. • By treatment of starch in excess water (<65% w/w) or intermediate water

content (40-50% w/w) at T below onset Tg for prolonged periods of time• The aim is to approach glass transition temperature which enhances

molecular mobility without trigggering gelatinizzation• Annealing elevates starch gelatinization temperature, decreases

gelatinization temperature range, and reduces swelling power.• Annealed starch granules contain more glassy amorphous regions

resulting in the restriction of starch granule hydration during gelatinization and elevation of gelatinization temperature

• Annealing affects the degree of susceptibility of starch to acid and enzymatic hydrolysis and the susceptibility varies with different starch sources.

Extrusion• Extrusion cooking is considered to be a high temperature short time (HTST) process• Extrusion process can be used to produce pregelatinized starch, in which granular

starch with different moisture contents is compressed into a dense, compact mass, and disrupted by the high pressure, heat, and shear during the process, forced to pass through a restricted opening at a pre-determined rate

• The extruded starch is further dried and ground to a desired particle size for food applications

• Water solubility and absorption are two main functional properties of extruded starches when they are dispersed in water. Two indices have been used to determine the capacity of starch solubility and water absorption.

• Extruded starch shows an increase in water solubility, but a decrease in water absorption (less able to form a gel).

• Extruded starch absorbs water rapidly to form a paste at room temperature. • Gels of extruded starch have lower retrogradation values than nonextruded gelatinized

starch

CHEMICAL MODIFICATION• changes the functionality of the starch with quite straightforward• Involves primarily reactions associated with the hydroxyl groups of the starch polymer.

Derivatization via ether or ester formation, oxidation of the hydroxyl groups to carbonyl or carboxylic groups, and hydrolysis of glycosidic bonds are some of the major mechanisms of chemical modification

• Chemical modification can be carried out on three starch states:1) In suspension, where the starch is dispersed in water, the chemical reaction is carried

out in water medium until desired properties are achieved. The suspension is then filtered, washed, and air dried.

2) In a paste, where the starch is gelatinized with chemicals in a small amount of water, the paste is stirred, and when the reaction is completed, the starch is air dried.

3) In the solid state, where dry starch is moisturized with chemicals in a water solution, air dried, and finally reacted at a high temperature (i.e., = 100°C).

• The most common chemical modification includes: oxidation, esterification, and etherification

• The extent of chemical modification is generally expressed as the degree of substitution (DS) when the substituent group (e.g., acetate or phosphate) reacts with the hydroxyl groups of the D-glucopyranosyl unit

oxidation• various oxidizing agents have been introduced, for instance,

sodium hypochlorite, hydrogen peroxide, periodate,, sodium chlorite etc

• The main uses for oxidized starch are the paper and textile industries. However, the application of oxidized starches in the food industry is increasing because of their low viscosity, high stability, clarity, and binding properties.

• oxidation occurs mainly in the amorphous phases of the granule

• Oxidation of starch mainly causes the scission of the glucosidic linkages and oxidation of hydroxyl groups to carbonyl and carboxyl groups.

• The scission of the glucosidic linkage results in depolymerization of amylose and amylopectin, hence decreases swelling power and paste viscosity.

• Since the bulkiness of the carboxyls and carbonyls sterically interfere with the tendency of amylose to associate and retrograde, oxidized starches produce pastes of greater clarity and stability than those of unmodified starch

• Oxidized starches are used as binding agents in foods and coating, such as batters applied to meats before frying.

These types of starches provide good adhesion of the batter to the food and a crispy texture after frying.

Cross linking• Cross-linking is done to restrict swelling of the starch granule under cooking

conditions or to prevent gelatinization of starch by reinforces hydrogen bonds in the granule with chemical bonds that act as a brifge between starch molecule

• Starch contains two types of hydroxyls, primary (6-OH) and secondary (2-OH and 3-OH). These hydroxyls are able to react with multifunctional reagents resulting in cross-linked starches

• The reagents permitted by FDA for making cross-linking food grade starch are phosphoryl chloride, sodium trimetaphosphate, adipic acetic mixed anhydride, and mixtures of sodium trimetaphosphate and tripolyphosphates.

• The chemically bonded cross-links may maintain granule integrity to keep the swollen granules intact, hence, prevents loss of viscosity and provides resistance to mechanical shear

• Starch with a low level of cross-linking shows a higher peak viscosity than that of native starch and reduced viscosity breakdown.

• Increasing the level of cross-linking eventually will reduce granule swelling and decrease viscosity. At high cross-linking levels, the cross-links completely prevent the granule from swelling and the starch cannot be gelatinized in boiling water even under autoclave conditions.

Cross linking• The key benefits of crosslinking, even at low levels, are

granular stability and improved paste texture• In general, as the level of crosslinking increases, the

starch becomes more resistant to the changes generally associated with cooking and pasting.

• Starch with a high level of crosslinking (high-DS starch) does not have a peak viscosity but rather shows a continual and progressive increase in viscosity throughout the cooking process.

• It is important to select the level of crosslink that allows for optimal performance in a particular system. For example, a starch that is highly crosslinked (i.e., highly inhibited) may not function appropriately in a system that receives a limited amount of heat.

• Cross-linked starches are used in salad dressings to provide thickening with stable viscosity at low pH and high shear during the homogenization process.

• Cross-linked starches have been applied in soups, gravies, sauces, baby foods, fruit filling, pudding, and deep fried foods

Substitution-stabilization• the viscosity of starch pastes tends to

increase upon cooling and aging.• This viscosity formation and textural

change can be extreme for certain types of amylose-containing starches. In fact, these starches can form rigid gels caused by the reassociation of amylose molecules.

• This reassociation of starch polymers is usually referred to as retrogradation .

• In order to minimize or prevent retrogradation, starch is substituted or stabilized by introducing monofunctional chemical “blocking groups,” such as acetyl or hydroxypropyl groups, along the polymer backbone

This modification results in the addition of a chemical blocking group between starch polymers and involving derivatization with a monofunctional reagent through ester or ether formation.

• Highly substituted starch is extremely freeze-thaw stable and has better paste clarity than its nonsubstituted native starch base.

• The clarity of the paste is improved by increasing the degree of swelling or hydration capacity of the starch granule and by reducing retrogradation

• Substitution lowers the gelatinization temperature and stabilizes the starch by preventing the reassociation, i.e., retrogradation, of polymers after cooking.

• Substituted starch is particularly useful for refrigerated and frozen food applications, since retrogradation is accelerated at cold temperatures, leading to opaque, gelled texture

esterification• Starch ester is a group of modified starches in which some hydroxyl groups have been

replaced by ester groups. • The level of substituents of the hydroxyl groups along the starch chains is often

expressed as average degree of substitution (DS). • The reagents approved by the FDA for preparation of organic and inorganic monoesters

of starch intended for food use are acetic anhydride, vinyl acetate, succinic anhydride, 1-octenyl succinic anhydride, and sodium tripolyphosphate

• In this section, three types of starch esters introduced:1) Starch acetates prepared by reacting starch with acetic anhydride low DS2) Starch succinate and starch alkenylsuccinate, which are produced by the reaction of starch with succinic anhydride and alkenyl substituted succinic anhydride, respectively3) Starch phosphate resulting from the reaction of starch with tripolyphosphate and/or trimetaphosphate

• Effect low temperature stability, high-thickening powder, low-gelatinization tempt., clarity, and reduce tendency to retrograde

• Cross-linked acetate starches are used as thickeners in baked, canned, frozen, and dry foods. They are also used in fruit and cream pie fillings, tarts, salad dressings, and gravies

etherification• Viscosity of ether linkages are more stable even at high pH. • hydroxypropyl starch which is made by reacting propylene

oxide with starch under alkaline conditions• The hydroxypropyl groups on starch chains may hinder

enzymatic attack and also make neighboring bonds resistant to degradation.

• Substitution of hydroxypropyl groups on starch chains disrupts the internal bond structure resulting in the reduction of the amount of energy needed to solubilize the starch in water. As a result, the pasting temperature of starch decreases with an increase in the level of hydroxypropyl substitution. When the DS reaches a certain level, the starch becomes cold water swelling

• Hydroxypropyl starches are being widely used in food products where they provide viscosity stability and freeze-thaw stability. Hydroxypropyl starches are used as thickeners in fruit pie fillings, puddings, gravies, sauces, and salad dressings.

• Hydroxypropyl starches are used as thickeners in fruit pie fillings, puddings, gravies, sauces, and salad dressings.

Acid hydrolysis• Acid hydrolysis of starch proceeds randomly, cleaving both a-1,4 and a-1,6 linkages

and shortening the chain length with time.• a-1,4 linkage and the amorphous regions containing a-1,6 linkage are more accessible

to acid penetration and hydrolysis. • Acid modification includes a two-stage attack on the granules:1) At the early stage, a rapid initial attack occurs on the amorphous regions of starch

containing branching points with a-1,6 linkage; an increase in linear fraction in starch is found in this stage.

2) A slower hydrolysis takes place on the more crystalline areas during the second stage

• Acid hydrolysis involves suspending starch in an aqueous solution of hydro-chloric acid (HCl) or sulfuric acid (H2SO) and maintaining at a temperature between ambient and just below the pasting temperature to prevent gelatinization.

• When the desired reduction in viscosity is obtained, the acid is neutralized and the starch recovered by filtration.

• The primary objective of acid hydrolysis is to reduce the hot viscosity of the starch paste so that higher concentrations of starch can be dispersed without excessive thickening. These products are commonly referred to as “thin-boiling” or acid thinned starches.

• In addition to low hot viscosity, high gel strength at high solids levels is another key attribute associated with acid-converted starches.

• These types of starches are particularly useful in confections where gelling is required

• Candies containing these starches typically have a soft, jellylike texture that is tender yet firm. The degree of hydrolysis can be optimized to control textural properties.

Pyroconversion (dextrinization)• Commercial pyrodextrins are generally produced by dry roasted acidified

starch in a reactor with good agitation. • Depending upon the reaction conditions (e.g., pH, moisture, temperature,

and length of treatment), pyroconversion produces a range of products that vary in viscosity, cold-water solubility, color, reducing sugar content, and stability.

• pyrodextrins are typically classified as white dextrins, yellow dextrins, and British gums, depending upon processing conditions and their resultant properties (1).

• Depending upon the conditions of dextrinization, both hydrolysis and repolymerization can occur.

• Pyroconversion generall creates new glycosidic bonds in addition to the existing a-1,4 and a-1,6 linkages.

• Because of their typically low viscosity, good film-forming ability, and high solubility in water, pyrodextrins are used in the coating of foods and can replace more costly gums in many of these applications.

Enzyme Hydrolysis• Enzymes hydrolyze (1→4) or (1→6) linkages between a-D-

glucopyranosyresidues. • There are many enzymes used in starch hydrolysis to alter starch structure and

to achieve desired functionality. • The most common enzymes for starch modification include a-amylase, ß-

amylase, glucoamylase, pullulanase, and isoamylase. • Starch hydrolysis involves liquefaction and saccharification of starch.1) Liquefaction is a process to convert a concentrated suspension of starch

granules into a solution of low viscosity by a-amylase.2) Saccharification converts starch or intermediate starch hydrolysis products to

D-glucose by enzymes such as glucoamylase (amyloglucosidase). • The reducing power of the product is a measure of the degree of starch

breakdown.• Dextrose equivalent (DE) is used to define the reducing power content

calculated as the percent anhydrous dextrose of the total dry substance. • The smaller the molecules, the sweeter the mixture and the higher the

dextrose equivalent (DE). The DE of starch is 0, and that of dextrose is 100.

• The most widely used enzymatic modification of starch is the conversion of starch to maltodextrins, corn syrups, and sugars (e.g., dextrose).

• There is a wide range of these products which vary depending on the size of the molecules in the final reaction mixture.

• Maltodextrins have a DE of less than 20 and corn syrup solids a DE of 20 or greater. • Starch conversion products can be provided in either the dry form or as syrups.

The removal of water from syrups to form dry powders is not easily accomplished. Because heating can cause discoloration of high-DE syrups, vacuum is often used in conjunction with heat to remove water. Often the production of dry products requires several purification, evaporation, crystallization, and filtration steps

• Many industrial applications involve the use of cyclodextrins to alter the apparent chemical and/or physical properties (e.g., solubility, volatility, or chemical stability) of the guest molecule in the Inclusion complex.

• a-Amylase cannot hydrolyze the a-1,6 glycosidic bonds that form the branch points in amylopectin, nor can it sever a-1,4 glycosidic bonds that

are in close proximity to a branch point.

• B-amylase (a-1,4-glucan maltohydrolase– enzymes cleaves alternate glycosidic bonds of starch in a-1,4 chains a non reducing sugar

• Glucoamylase (a-1,4-glucan glucohydrolase)—Enzyme that removes the glucose units consecutively from the nonreducing ends of starch polymers by hydrolyzing both a-1,4 and a-1,6 linkages.

• Debranching enzyme— Enzyme, such as isoamylase and pullulanase, that hydrolyzes the a-1,6 linkages of starch.