Gelation of starch

In order to prepare thermoplastic starch, the crystal structure of starch has to be destroyed, either by mechanical working, pressure or heat, or by addition of plasticizers, such as water and glycerin. The gelation of starch is the disruption of the semicrystalline structure of its granules during heating in the presence of water over 90% [32], The gelation process occurs... 

Rubens, P., Snauwaert, J., Heremans, K., et al. (1999). Insitu Observation of Pressure-induced Gelation of Starches Studied with IR in The Diamond Anvil Cell. 

A second reason for the turn-over in the osmotic modulus may arise from a decrease in A2 until it becomes zero or even negative. This would be the classical situation for a phase separation. The reason why in a good solvent such a phase separation should occur has not yet been elucidated and remains to be answered by a fundamental theory. In one case the reason seems to be clear. This is that of starches where the branched amylopectin coexists with a certain fraction of the linear amylose. Amylose is well known to form no stable solution in water. In its amorphous stage it can be brought into solution, but it then quickly undergoes a liquid-solid transition. Thus in starches the amylose content makes the amylopectin solution unstable and finally causes gelation that actually is a kinetically inhibited phase transition [166]. Because of the not yet fully clarified situation this turn-over will be not discussed any further. 

Chilton, W. G., Collison, R. (1974). Hydration and gelation of modified potato starches. Food TechnoL, 9,87-93. 

Fig. 3.—Characteristics of gelation of potato starch.20 ( ) Air dried, (—) oven dried, (--)...

Fig, 7.—Upward shift of the gelation temperature of starch granules under the influence of high pressure (from Ref. 58). 

Mild acid modification of oat starch had a great affect on the viscoelastic behavior of pastes during cooling. Acid-modified oat starch underwent one transition in viscoelastic behavior below 40°C, G increased and 6 decreased, due to gelation of amylose. The transition below 90°C typical for native oat starch was not observed after acid modification. This finding is in agreement with that of Paton,43 who found that treatment with acid almost eliminated the exceptionally high viscosity measured at 80°C for native oat starch. 

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