Starch Widely used as a food ingredient for many

purposes. A very wide selection of starches, both

native and modified (National Starch has >200 different starches for sale for selected application)

Starch gelation and pasting characteristics altered by other ingredients and by processing conditions

Unheated starch granule

Heated starch granule

Starch Forms Starch is the primary carbohydrate source

for growing seeds and leaf tissue development and is found in leaves, tubers, fruits and seeds.

Two general types of starch exist – amylose and amylopectin. Both are polymers of glucopyranose molecules, but differ in structure and functional properties,

Characteristics of Amylose and Amylopectin

Form Essentially linear

Branched

Linkage -1,4 (some -1,6)

-1,4; -1,6

Polymer units 200-2,000 Up to 2,000,000

Molecular weight Generally <0.5 million

50-500 million

Gel formation Firm Non-gelling to soft

Characteristic Amylose Amylospectin

Amylose

Amylopectin

Amylopectin General Structure

Amylopectin structure (Chaplin, 2004)

Crystal Structure Forms The form depends upon the source of the granules. Type A crystal structure is found in most cereals,

whereas Type B is found in some tubers and high amylose

cereal starches. Some plants have both A and B and are

desginated Type C. When starches are heated in the presence of lipid, a different crystal structure may be formed, which is called Type V.

Types of crystal structure in amylopectin (Chaplin, 2004).

Native Starches The most common native starches are corn (maize), rice,

wheat, potato, tapioca (cassava) and waxy maize. Except for waxy maize, these starches generally contain from

15-27% amylose. Waxy maize and other waxy native starches generally contain

less than 2% amylose. High amylose starches contain more than 30% amylose and

have quite different properties. They:   Are difficult to gelatinise > 100° C Can form films and fibres            Have more helical structure - may entrap fatty acids –

retards granule swelling

Differences in Native Starches

Vary in amylose and amylopectin content Vary in crystal structure Vary in gelation and pasting characteristics Vary in minor components that can be incorporated

within the structure of amlyose and amylopectin– Phoshate esters – Phospholipids– Proteins

Starch Viscosity, mild heat, neutral

Viscosity, high heat, acidic

Shear resistance

Freeze-thaw stability

Comments

Tapioca (N) 3 3 5 3 Bland flavoured, fillings and canned

Tapioca (N) 3 3 5 2 Process tolerant, short texture; dairy products, soups and sauces

Tapioca (CL) 4 4 4 6 High viscosity, dairy products

Potato 6 2 2 2 Rapid hydration, high viscosity; meat, sauces snacks

Corn 3 4 5 3 Process tolerant, low hot viscosity; dressings and cereals

Waxy maize, cross linked

4 5 4 6 Freeze thaw stability; frozen foods, fillings and sauces

Types of Food Starches

Unmodified Native starches: Corn, wheat, etc. Pregelatinized starches Modified Acid thinned - hydrolyze to reduce molecular weight Crosslinked - Chemically linking OH's from two adjacent

molecules. Toughens granule. Adds acid and heat stability Derivatized - Add bulky groups to starch to reduce

retrogradation. Changes hydrophobicity Crosslinked-Derivatized - Does both Oxidized - reduces retrogradation.

Modified Starches

Cross-linked starches make up about 25% of all starches used in foods. The four major cross-linking agents are shown in Table 7. In addition to different cross-linking agents, the degree of cross-linking varies. The details of the cross-linking of commercial starches remain proprietary to the company making the starch.Table 7: Cross-Linking Agents for Starch

Epichlorhydrin Starch - O-CH2-CHOH-CH2-O-Starch

Sodium Trimetaphosphate Starch - O-P-O-Starch

Phosphorus Oxychloride Starch - O-P-O-Starch

Reagent Derivative

Acrolein Starch-O-CH2-CH2-C-O-Starch

 

Cross-linked starches make up about 25% of all starches used in foods. The four major cross-linking agents are shown below. In addition to different cross-linking agents, the degree of cross-linking varies. The details of the cross-linking of commercial starches remain proprietary to the company making the starch.

Reagent Derivative     Epichlorohydrin Starch - O-CH2-CHOH-CH2-O-Starch Sodium Trimetaphosphate Starch - O-P-O-Starch Phosphorus OxychlorideStarch - O-P-O-Starch Acrolein Starch-O-CH2-CH2-C-O-Starch

Derivitized Starches

The five primary derivatized starches, the derivatising agents and the degree of substitution are shown in the following table. The starch properties will vary with the type of derivatised starch and the degree of substitution. Many companies made “double derivatized” starches that are both cross-linked and derivatized.

Derivatizing Reagents

Reagent Derivative D.S.       Acetic anhydride Starch acetate 0.05 -

0.10 Vinyl acetate Starch acetate 0.05 -

0.10 Propylene Oxide Hydroxylpropyl starch 0.05 - 0.20 Sodium tripolyphosphate Starch phosphate 0.01 -

0.02 Succinic anhydride Succinylated starch 0.02 -

0.05

Gelatinization and Pasting

“Starch gelatinisation is the collapse (disruption of molecular order) within the starch granule, manifested in irreversible changes in properties such as granular swelling, native crystalline melting, loss of birefringence and starch solubilisation. The point of initial gelation and the range over which it occurs is governed by the starch type, concentration, method of observation, granular type and heterogeneities within the granule population under observation.”

“Pasting is the phenomenon following gelatinisation in the dissociation of starch. It involves granular swelling, exudation of molecular components from the granule; and eventually the total disruption of the granules”

Factors Affecting Hydration

Amount of water   Availability of water   Time and Temperature of heating   Starch type     Corn vs. rice etc.   Crosslinking   Derivitization   Pregelatinization pH   Saturated monoglycerides  

Problems

Failure to hydrate Retrogradation Amylases Loss of viscosity

Amylose

Swelling Collapse AggregationC

Viscosity E

D

B

ATime

A = Paste initiation temperature

B = Peak Paste Time

C = Peak Viscosity

D/C = Stability ratio

E/D = Set back ratio

50 65Temp 90 95 80

Amylose

Swelling Collapse AggregationC

Viscosity E

D

B

ATime

A = Paste initiation temperature

B = Peak Paste Time

C = Peak Viscosity

D/C = Stability ratio

E/D = Set back ratio

50 65Temp 90 95 80

Amylose

Swelling Collapse AggregationC

Viscosity E

D

B

ATime

A = Paste initiation temperature

B = Peak Paste Time

C = Peak Viscosity

D/C = Stability ratio

E/D = Set back ratio

A = Paste initiation temperature

B = Peak Paste Time

C = Peak Viscosity

D/C = Stability ratio

E/D = Set back ratio

50 65Temp 90 95 8050 65Temp 90 95 80

Starch Gelation and Pasting

Pasting Cycle

Pasting characteristics of different native starches

(from Food Additives, 2nd Ed 2002, Brane et al. Eds)

Gelatinization of starches

Type % Amylopectin % Amylose Gelatinization Range °C Granule Size

          Corn 73 27 62-72 5-25 Waxy Corn 99 1 63-72 5-25 High Amylose 20-45 55-80 67-100+ 5-25 Potato 78 22 58-67 5-100 Rice 83 17 62-78 2-5 Tapioca 82 18 51-65 5-35 Wheat 76 24 58-64 11-41

Paste Properties of Native Starches

Starch Type Viscosity Clarity Gel Shear Stability           Cereal         Regular Short Opaque Strong Good Waxy Long Clear V Weak Poor Root, tuber   Clear-opaque Weak Poor High Amylose V Short V Opaque V Strong Stable  

Summary of cornstarch paste properties

Type Comments

Native Poor freeze thaw stability

High amylose Granules- birefringent

Acid modified Decreased hot paste viscosity

Hydroxy-ethyl Increased paste viscosity - low retrogradation

Phosphate Reduced gel at refrigeration temperature - low retrogradation

Cross-linked Reduced peak viscosity, increased stability; freeze thaw stability

Acetylated Good paste clarity and stability

Exogenous and Endogenous Effects on Starch Pasting Characteristics

Acid pH Sugar Lipids Proteins Shear

Vis

cosi

ty

Time

Cornstarch + water

Cornstarch + water + 1.7% acetic acid

Vis

cosi

ty

Time

Cornstarch + water

Cornstarch + water + 1.7% acetic acid

Vis

cosi

ty

Time

Cornstarch + water

Cornstarch + water + 1.7% acetic acid

Effect of Acid on Starch Pasting

pH 4

pH 10

pH 2.5

Vis

cosi

ty

Time

pH 4

pH 10

pH 2.5

Vis

cosi

ty

Time

Effect of pH on Pasting of Corn Starch

Effect of Sugars on Pasting of Corn Starch

Processing Effects

• Processes that are known to affect the pasting characteristics of starches include:            Order of addition of ingredients            Temperature achieved            Rate of temperature rise            Duration of heating            Rate of cooling            Storage temperature            Shear

Retrogradation Solubilised starch polymer and remaining insoluble

granular fragment tend to re-associate after heating. The re-associating is termed “Retrogradation”.

Retrogradation has been defined as follows: “Retrogradation is a process which occurs when starch

chains start to re-associate into an ordered structure. In its initial phase, two or more starch chains may form a simple junction point, which then may develop into more extensively ordered regions. Ultimately, under favourable conditions, a crystalline order appears.”

Generally, amylose-containing starches show greater retrogradation. Factors relating to retrogradation include:

Factors relating to retrogradation include:

· Amount of branching · High amylopectin starches - e.g., waxy maize

shows no retrogradation when frozen · Hydrogen bonding between OH groups in

amylose in gelatinised starches during cooling · Water forced out of gel structure (syneresis) & Starch insolubilized.

Amylopectin also plays a role in retrogradation over time. Short-term retrogradation is largely associated with amylose (which reaches a limit in 2 days), whereas long-term retrogradation is thought to involved amylopectin (reaching a limit is 40 days)

The botanical source is important in respect to retrogradation, not only for starches that differ in amylose content, but also for starches with very similar amylose content.

For retrogradation to occur there must first be an aggregation of the chains.

Amylopectin from potato and tapioca (B type starches) retrograde to different degrees and this has been related to difference in short branch chains.

Functions of starch in food systems and examples of how these are utilised in different food systems.

Function Example

Thickener Puddings, sauces, pie fillings

Binder Formed meats; breaded items; pasta

Gelling agents Confections

Encapsulation, Emulsion Stabilizer

Flavours, bottlers emulsions

Coating Candies, glazes, icings and toppings

Water Binder Cakes

Free Lowing/Bulking Agent

Baking powder

Releasing Agent Candy making

Texture modifier Processed cheese, meat products

Fat Replacer Salad dressings, dairy products, baked goods

Applications The amount of starch used in different types

of foods ranges from 0.2% in beverage products to 12% is some candies. Use levels, except for gums & candies, generally fall into two general categories.

<1%: beverages, butter sauces, cake mix and icing and marshmallows

2 – 5%: baby foods, spoonable salad dressings, Harvard style beets and creamed soups, cheese analogs

Approximate Amount of Starch in Food Products (%)

Baby foods 3-5 Beverages (bottler's emulsions) 0.2-0.3 Butter sauces 0.3-0.5 Cake mix and icings0.3-0.5 Dressings 

– Pourable 1.5-2.3– Spoonable 2.8-5.0

Gum candy 5-12 Harvard style beets 2-4 Marshmallows 0.5-1.0 Pie crust 0.5-1.2 Pie filling 3-5 Pudding  

– Canned 4.5-6.5– Cooked 5-8– Instant 3-7

Sauces     Thick 4-6   Gravy 1.0-2.5

Lots of Choices

In the selection of a starch for a food application, consideration

needs to be given to:

            Flavour            Texture            Body            Appearance

In the selection of a starch for a food application, consideration

needs to be given to:

Formulation How long is the shelf life of the food High Acid or Low Acid Processing conditions

– High heat vs low heat– High shear vs low shear– Both high heat and high shear

Other Questions to ask in Selecting a Starch

      Is there sufficient moisture to hydrate the starch?            Is the solids level to low or too high?            How will lipids affect the starch and the resulting food?            What salts and what salt levels are required in the food?            What type and level of sugar is being used?            Are there other hydrocolloids included in the formulation?

Origin Type Application

Function Benefit

Corn Native Soup mixes

Thickener Body, mouth feel

Corn Pre-gelled Puffed snacks

Texture Improved processing

Waxy maize

Cross linked

Salad dressing

Stabiliser Body, gloss, stability

Tapioca Cold water swelling

Instant dairy products

Texture Bland flavour, premium cook up texture

Potato Native, cook up

Dry mixes

Thickener Rapid hydration, high viscosity

Source, type, application, function and benefits of some starches in selected foods.

Starch types for different foods and applications

Application Binding Viscosity building

Film formation

Texturising

Soups and sauces

- X, XS, PX, PXS

-- X, XS, PX, PXS

Bakery PN X, P, PX, PXS D, M P, X, PX, PXS, M

Dairy N, A, M, X, XS, P, PX, PXS

-- X, XS, PXS, A, NX, O, PO, M

Snacks N, P, PN, PO, D

--- --- --

Batters & coatings

X, PX, O P, PX D O, PO, D. M

Meat products N, X, XS, P ---- XS XS

N=native; X = cross-linked; P=pregelatinised; S=substituted (derivatised); O=oxidised; A=acid hydrolysed; D=dextrin; M=maltodextrin. Where letters are together without a comma, all types are combined into a single product. 

Selection of starches for dairy foods

Product Requirements Best Starch Type Comments

General Dairy

Heat tolerant, shear tolerant, freeze-thaw stable, bland flavour

Cross-linked and substituted

Tapioca best from a flavour viewpoint

UHT products More heat & shear tolerant

Increase degree of cross-linking

 

Frozen desserts

Freeze-thaw stability most important

Substituted Fat replacers in low fat products, cross-linked for better freeze thaw stability

Dry mix applications

Perform under low heating conditions

Pregelled, low level of cross-linking, freeze- thaw stability

Instant puddings and cheese sauces most common usage

Yoghurt Acid stable Cross-linked Used to minimise syneresis

Processed cheese

Gelling characteristics Cross-linked waxy maize

 

Problem Possible causes Possible solutions

Syneresis Poor freeze thaw stability; colloid system breakdown

Decrease shear; Increase starch level, Increase cooking time and/or temperature; Use stabilised starch

Runny texture Low solids content Increase starch; select different starch; decrease shear; check for amylases in other ingredients

Graininess Starch not cooked Consider pregelled starch. Adjust water; adjust processing time and/or temperature

Common problems, causes and possible solutions for dairy foods

Product Requirements Best Starch Type

Comments

Cereals “Bowl” stability High amylose starch

 

Expanded snacks

Good expansion Light to moderate cross- linked starch

 

“Half” product Shear stability Pregelled, cold water swelling, moderate cross linked

Single screw extrusion followed by baking

Twin screw extruded products

Shear, pressure and temp. stability

Cross linked “cook-up” starches

 

Selection of starches for extruded products

Common problems, causes and possible solutions for extruded products

Problem Possible causes Possible solutions

Lack of crispness Weak expansion Increase amylose if product exposed to high shear

Poor cutting or shape Low dough viscosity or strength

Increase amylosefor high shear; Increase amylopectin for low shear adjust moisture content

Non-uniform sheet thickness

High water absorption Decrease water content; choose starch with low water holding capacity

Selection of starches for meat products

Product Requirements Best Starch Type

Comments

Bologna & frankfurters

High viscosity, high water holding capacity

Lightly or moderately cross linked and substituted

need to have products that are freeze/thaw stable

Surimi, cold applications

High water holding capacity

Blends of native and modified amylose- containing starches

Used as a filler; blends used to improve moistness of the gel

Surimi, hot applications

High water holding capacity

Blends of native and modified waxy starch

Used as a filler; blends used to improve gel moistness

Common problems, causes and possible solutions for meat products

 Problem Possible causes Possible solutions

Poor water holding capacity

Lack of water-binding components

Add substituted, stabilised starch; use starch with high water binding capacity

Low freeze-thaw stability

Low level of modification

Increase degree of cross linking and or substitution

Poor bite, soft texture Structure not fully developed

Check starch selection; add substituted, stabilised starch

Take Home Starches are very complex Selection of a starch is related to the type of food and

processing conditions Lots of choices – different starches (both native and

modified) give different characteristics to the food Modified starches generally used when you need:

– Resistance to shear– Resistance to heat– Resistance to acid– Reduced retrogradation– Product expected to have a very long shelf-life