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
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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.
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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
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.
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.
“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
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
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.
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
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