Swelling of starches
Related to amount of branching
High amylopectin starches - eg, waxy maize - no retrogradation when frozen
Hydrogen bonding between OH groups in amylose in gelatinized starches during cooling.
Water forced out of gel structure
Starch insolubilized.
Intermolecular bonds break with increasing temperature
H bonding sites engage more water
Increased randomness in structure
Decrease in crystallion regions
Loss of birefringence
Difficult to gelatinize > 100° C
Can form films and fibers
Greater solubility and swelling under alkaline conditions
Helical structure - may entrap fatty acids - retards granule swelling
Oligosaccharides
2-10 sugar molecules
Dissacharides
Homogenous - based on D-glucose
Maltose
Isomaltose
Trisaccharides
Maltotriose
Raffinose
Heterogenous
Lactose
4-0-beta-D-galactopyranosly-D-glucose
alpha-lactose - crystallizes from water at ambient temperature
beta-lactose - crystallizes at temperatures above 95° C
Sucrose
alpha-D-glucopyranosyl- beta-D-fructofuranoside Summary of
corn starch properties
| Normal | Poor freeze thaw stability |
| High amylose | Granules- birefrigent |
| Acid modified | Decreased hot paste viscosity |
| Hydroxyethyl | Increased paste viscosity - low retrogradation |
| Phosphate | Reduced gel at refirgeration temperature - low retrogradation |
| Cross-linked | Reduced peak viscosity, increased stability |
| Acetylated | Good paste clarity and stability |
Modification of starches
Acid conversion.
Amylopectin > amylose.
Hot concentrated pastes.
Gel formation on cooling.
Gum candies.
Decreased hot paste viscosity.
Decreased gel strength.
Increased gelatinization temperature.
Hydroxyethyl straches.
Reduced gelatinization temperature.
Increased rate of swelling.
Lower tendency of pastes and gels to retrograde.
Hydroxy propyl starches
Propylene oxide.
Salad dressings, pie fillings, thickening.
Starch phosphates -
Lower gelatinization temperature
swelling in cold water
increased paste viscosity
decreased retrogradation.
Starch acetates
inhibit association of amylose and long chains of amylopectin.
Low D.S. 0.05 - 0.10
Low gelatinization temperature.
Resists retrogradation after pasting and cooling.
Cross-linked starches. Diesters or links between OH groups in
adjacent chains.
Uses of cross-linked starches
Stability to heat, agitation, hydrolysis, low pH.
Swelling can be inhibited in hot or boiling water.
Used in infant foods, pie fillings, salad dressings, stabilizers and thickeners.
Cross- linking agents:
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 |
Interactions of starch
Sugar affects Aw
High concentrations
Decrease peak viscosity
Decrease rate of swelling
Decrease gel strength and make the gels more elastic
Dissacharides>monosaccharides in retarding gelatinization and reducing gel strength.
Effect of sugars on starch viscosity
5% corn starch at 100° C
Interactions with lipids
Fatty acids and lipid emulsifiers (lecithin, mono and di
glycerides) may form inclusion complexes with helical amylose
structures.
Starches as fat substitutes - Gels of enzyme converted starch (DE
<5) show fat-like properties
Maltodextrans MW approximately 8,000.
