Polysaccharides - Starch

7 important questions on Polysaccharides - Starch

What are sources of starch?

Potato, corn, rice, wheat

What is the starch composition?

Amylose (20-30%) and amylopectin (70-80%). The DP of amylose (800-3000) is much smaller than the DP of amylopectin (2*10^6).

What happens if you add starch to cold water?

It doesn't dissolve. You have to heat it, then it gelatinises and the starch is dissolved.

Gelatinization of starch
  1. Gelatinization temperature
  2. Loss of polarisation cross
  3. Peak viscosity
  4. Disruption of starch granules

Retrogradation when cooling --> increasing viscosity, molecules connect again with each other (irreversible)

What are 4 modifications of starch?

  • Instant starch
  • Thin-boiling starch
  • Cross-linked starch
  • Substituted starch

How is instant starch made?

Physical modification: fast heating + drying.
Native starch: insoluble in cold water
Instant starch: soluble in cold water

How is thin-boiling starch made?

Chemical modification: partial hydrolysis by e.g. Acid
Native starch: large starch molecules, give high viscosity
Thin-boiling starch: smaller molecules, lower viscosity

How is cross-linked starch made?

Chemical modification: cross-linking with eg. Phosphate
Native starch: original starch molecules
Cross-linked starch: less sensitive to stirring (soup)

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