BASIC PROPERTY OF RAW STARCH
| Solubility |
As starch is not soluble in water, it can easily extracts in water from
the storage in plant. Its suspension starts to become viscous by heating
and turns to transparent paste. It means amylopectin forms crystallized
micelle and amylose arranges orderly around the gaps of the micelles in
starch particle. This is why starch is not soluble in cold water. However, water molecules are getting into micelles gradually when heating the solution and resulting to loosen hydrogen bond and short molecules of amylose starts to dissolve, then amylopectin swells up. |
Gelatinization
& Retrogradation |
Starch is swelling up by heating and continues to swell up absorbing water
and showing more viscosity and clarity along with increase of temperature
and then will reach to maximum viscosity. By giving further higher temperatures,
the outer shell of starch particle which have highest cristallinity index
starts to collapse and amylopectin and amylose inside outer shell are melting
out and its viscosity is getting lower by heating and stirring.
Viscosity is gradually increasing again when the
solution is chilled down and continuous chilling makes the solution cloud and
less clarity. Leaving to stand the solution, it shows more white and in case of
higher concentration of starch, it gels and in case of low
concentration, syneresis and precipitation will be caused. This is the
retrogradation of starch caused by recrystallization of amylose through
cooling. |
| Viscosity |
The solution of starch which is gelatinized by high temperatures shows high viscosity and non-Newtonian flow. This indicates
the decrease of apparent viscosity when the shearing stress is faster and
this is considered an interaction of swollen starch particles. Thixotropic
viscosity of potato starch, which has thread forming property is termed“long”and plastic flow viscosity such as cornstarch, which has less thread forming property is termed“short”. |
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