selecting optimal starch[1]

7/29/2019 Selecting Optimal Starch[1]

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Selecting an Optimum Starch for Snack Development

David Huang

National Starch and Chemical Company

Bridgewater, NJ

Specialty starches have the potential for tremendous processing, textural, and mouthfeel

advantages in snack development. With dozens of food starches available, it can be

difficult to know which one will best meet a particular functional challenge. This articlegives some guidance on how to select an ideal starch for a particular type of snack and

specific attribute.

Baked Snacks

Key concerns for developers of baked snacks include texture, product shape, and surface

color. Baking develops the product's structure, makes it edible, and makes it aestheticallydesirable. Baking concerns encompass internal product temperature, which increases

slowly compared with extrusion or frying. Slow heating means pregelatinized starches,also known as instant or cold-water-swelling starches are needed for this application.

These starches are preferred because of the slow cooking process and because there is aminimum of water in the snack dough.

With their fine starch granule size, waxy-based starches are most suitable for baked snackproducts because tests show they permit easy sheeting and good binding, which results in

minimal breakage. Carefully chosen specialty starches can improve texture and forming

and reduce cracking and breakage. For texture improvement, a modified, pregelatinizedstarch derived from waxy maize will serve well. To minimize forming and shaping

problems, a bland, modified food starch that mimics fat or a modified, cold-water-

swelling starch will give good results. Resistant starches (see sidebar on resistantstarches) and high-amylose corn starch and modified high-amylose starches (see sidebaron amylose and amylopectin) can be used to reduce cracking and breakage that result in

excessive losses.

Fried Snacks

Frying cooks a product to make it edible and dehydrates the product, creating a unique

texture and pleasing mouthfeel. Oil temperatures typically reach 204- 260C (400-

500F), and processing time is short due to fast heat transfer. Under- or over- frying mayaffect texture and color. The use of an appropriate specialty starch for fried snacks can

result in better texture, mouthfeel, and reduced oil absorption. Cross-linked or modified

starches prevent the disruption of starch granules that can lead to poor texture andtoothpacking in the mouth. With proper modification, specialty starches made from

waxy maize, corn, and tapioca may be used to prevent these problems. High-amylose

starches sometimes are used as coatings and may reduce oil absorption during frying

because of their strong film forming characteristics. Modified high-performance resistantstarches can provide these functions.


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Extruded Snacks

Moist, starchy ingredients heated and sheared at high temperatures and pressure produce

a melted, putty-like dough that expands when the pressure is released. By manipulatingthe ratio of high-amylose to high-amylopectin starch, a target texture can be achieved.

Generally, native starches cannot resist the high temperatures and high shear associated

with extrusion. In contrast, cross-linked starches can resist shear and very hightemperatures. However, excessively cross-linked starches lower the starch granules

swelling capacity, resulting in a snack with reduced expansion and nonuniform texture.

Thus, a snack developer must select from many potential cook-up starches, includingthose made from corn, tapioca, and waxy maize. To select the best starch for the

application, developers need to correctly quantify their maximum shear and know the

temperature range in the extruder. If a snack developer can tell a starch manufacturer the

degree of shear, the temperature, and any preferences for the starch base, a quickrecommendation can be made. If a snack developer increases the amylose content of an

extruded snack formula, the snack will be firmer, more crunchy, and harder. However,

These gains will be made at the expense of expansion, which declines as the percentage

of amylose increases. An increase in amylopectin, on the other hand, increases snackexpansion and softness. For puffed snacks, the optimum cross-linked waxy corn starch

can help control expansion and increase product uniformity.

Half Products and Pellet Snacks

Snack pellets and half products are typically made from corn and other starches, usually

blended, and processed or cooked in long-barrel twin-screw (TS) cooker extruders.Cooking is followed by jacket cooling or venting, without puffing. The product is dried

under controlled humidity and matured for moisture equalization. Expansion may be

accomplished through frying, hot air, or microwave emission. The advantages of halfproducts for both producers and consumers include inexpensive and easy shipping and

low risk of breakage during shipping. After shipping, the product can be completed and

flavorings can be added that accommodate geographical preferences. Producers alsobenefit from reduced capital investment for different production locations.

Specialty starches can be used to improve half-product texture and flavor. In processing

half products, specialty starches can be used to rapidly increase viscosity in a TS extruderand bind various flours. Also, a starch can act as a seal on the pellet surface, enabling

more consistent expansion by frying or baking. For increasing viscosity, expansion and

binding, a pregelatinized, modified waxy maize starch, a cold-water-swelling modifiedwaxy maize starch, and a pregelatinized, modified tapioca starch are good choices. For

density control, resistant starches, modified high-amylose corn starch, or, in some cases,

unmodified high-amylose corn starch will serve well.

It is sometimes desirable to use starch combinations to achieve a variety of attributes.

Some proponents think that the longer starch chains found in potato or cassava starchesimprove the seal on the pellet exterior, which may lead to more uniform expansion during

baking or frying. A snack developer may try adding potato or waxy starch to rice meal to

create extrudates that have improved texture and desirable properties.


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Film Forming, Sheen, Protection, and Bonding

If resistance to breakage, sheen, and bonding of flavors and other foods are important

product attributes, then specialty starches can also play a role. A powder made from waxycorn starch solids forms a film on foods to hold spices or bits of other foods on the

substrate-food surface. Used on cookies, the powder creates a film with a glossy sheen.

For example, tomato bits, spices, and cheese slivers can be held firmly to a cracker.Small fruit bits also can be bonded to a cracker with this type of powder. In another case,

baked or fried snacks coated with this type of product are more resistant to breakage

during transport and handling. The strong film formed on the surface protects the snackfrom cracking due to vibration and impact. Originally developed to hold finely powdered

spices on snacks, this type of product also creates an attractive sheen and minimizes

breakage of fragile snacks, so consumers can open a container with more unbroken full-

size snacks.

This type of specialty starch also successfully holds larger bits on snacks and other foods.

For example, this type of specialty starch creates a bond strong enough to hold sesame or

poppy seeds on a bun or roll and creates a sheen that makes the product look homemade.

In an age when fusion cuisine is increasingly accepted, the possibilities for combiningfoods are growing more exciting thanks to this type of product. No special equipment is

needed for spraying the starch powder on foods, and the drying time ranges from a few

seconds to a few minutes, depending on the thickness of the film and the temperature

during heating.

Conclusions

The role of specialty starches in snack foods includes texture improvement, greaterexpansion, enhanced crispness, improved adhesion of flavors and food bits, reduced

breakage, processing aid or dough enhancement, and improved surface appearance. The

information provided here can serve as a guide for selecting the optimum specialty starchfor a specific application. Starch manufacturers often offer samples of their products.

With this knowledge, snack developers are more likely to successfully pick several

samples that will meet their specifications. Testing several starches rather than the

hundreds that are available can save significant time and reduce frustration whilebringing a new snack to market or troubleshooting a process to optimize snack

performance and minimize waste.

Reference

1. Yue, P., and Waring, S. Resistant starch in food applications. Cereal Foods World

43: 690, 1998

David P. Huang

David P. Huang is the cereal and snack business manager at National Starch andChemical Company in Bridgewater, NJ. He received his M.S. and Ph.D. degrees in food

science from Michigan State University in 1979 and 1982, respectively, and an M.B.A.

degree from Farleigh Dickinson University in 1990. Before joining National Starch, he

was general manager for H.J. Heinz.


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Amylose and Amylopectin

Amylose. Amylose is one of two starch fractions (Fig. 1 shows a chemists view of thefraction). Amylose forms cohesive gels, because of its long chains and readily receives

hydrophobic compounds such as lipids and mono- and diglycerides.

The glucose straight chains found in amylose are packed tightly together. Its

anhydroglucose units are linked by alphaD-1, 4 glucosidic bonds and form linear chains.

The level of amylose and its molecular weight vary among starch types. Amylosemolecules are typically made up of from 200 to 2,000 anhydroglucose units. Aqueous

solutions of amylose are very unstable due to intermolecular attraction and association of

neighboring amylose molecules, which leads to an increase in viscosity, retrogradation,

and under specific conditions, precipitation of amylose particles.

Retrogradation is the irreversible insolubilization of starch paste with formation of a

precipitate or gel, depending on concentration. Retrogradation is mainly due to the

presence of amylose in the starch. The linear amylose molecules are attracted to eachother and form bundles of parallel polysaccharide chains through the formation of

hydrogen bonds between hydroxyl groups on neighboring molecules. The tendency ofamylose molecules to retrograde is increased by molecular weight reduction to a chain

length of around 100 anhydroglucose units. Amylopectin, which has a branched

structure, shows less tendency to retrograde. Retrogradation occurs during baking,

extrusion, and frying of snack product, resulting in a light crisp texture.

Amylopectin. Amylopectin is the second of the two starch fractions. Figure 2 shows the

branching that identifies the fraction. Amylopectin is a constituent of starch that has apolymeric, branched structure. Because of this branched structure, amylopectin delays or

prevents gel formation, and retrogradation is slower than with amylose. Amylopectin

pastes appear stickier than high-amylose pastes. In addition to the 1,4 bonds, that arepresent in amylose and the linear segments found in amylopectin, the amylopectin

molecule has alpha-D-1,6 bonds that occur every 20-30 anhydroglucose units. Aqueous

solutions of amylopectin are characterized by high viscosity, clarity, stability, and

resistance to gelling. The level of amylopectin varies among different starch types.Waxy starches are almost 100% amylopectin. Table I shows the percentage of amylose

and amylopectin by starch base. Typically, waxy starch pastes provide a cohesive,

gummy texture and are considered nongelling. Used in rice crackers, waxy rice helpsimpart a light texture, while amylose rice types are better for heavier snacks.


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Fig. 1. Chemists conception of a short segment of an amylose chain.

Fig. 2 Chemists conception of a segment of amylopectin showing branching of chains.

2 2

O

CH

OH

OH

2O

2


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Table I. Percentage of Amylose and Amylopectin by Starch Base

Source Percentage Amylose Percentage Amylopectin

Corn 25 75

Waxy Corn < 1 > 99

High Amylose Corn 55 70 30 - 45

Potato 20 80

Rice 19 81

Waxy Rice > 1 > 99

Tapioca/Cassava/Manioc 17 83

Wheat 25 75

Sorghum 25 75

Waxy Sorghum < 1 > 99

Heterowaxy Sorghum < 20 > 80

Resistant Starches

Resistant starches resist the effects of digestive enzymes and are not digested in the smallintestine. When consumed, resistant starch acts more like a fiber in the human diet.

Standard methods for analyzing total dietary fiber in ingredients and foods can be used to

analyze resistant starch. Naturally found in many cereal grains, fruits, and vegetables,resistant starch can be used in some processed foods, such as cheese curls, pretzels, and

tortilla chips. Figure 3 provides some details about resistant starches. As a snack food

ingredient, resistant starches contribute to low water-holding capacity, excellent

expansion, easier processing, improved overall eating quality and bland, unobtrusive tasteand color. When snack developers would like to include a label claim of Good source

of high fiber, they may want to consider resistant starches, because they permit this type

of claim. Resistant starches may be used alone as a fiber source or with other food fibers.Yue and Waring (1) provide more information on uses of resistant starch in food

applications.


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Fig.3. Schematic diagrams and definitions of resistant starch classes.


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Table II. Some specialty starch choices for baked snacks by function.

Table III. Some specialty starch choices for fried snacks by function.

Table IV. Some cook-up specialty starches by degree of shear and temperature by starch

base.

selecting optimal starch[1]

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