Differential scanning calorimetric and rheological study of the gelatinization of starch granules embedded in a gel matrix
1992
Liu, H. | Lelievre, J.
The gelatinization of rice starch granules embedded in a gellan matrix or a gellan-locust bean gum matrix was investigated by differential scanning calorimetry. The same trends were found irrespective of which gel matrix was present. In the presence of the gel, the size of the endotherm per unit weight of starch appeared to decrease slightly as the concentration of the nonstarch polymer was increased, suggesting that restrictions to the extent of conformational disordering occurred. The biphasic endotherm characteristic of starch melting in concentrated starch-water mixtures was modified slightly and tended to appear more like a single peak in the presence of the gel. This may have been due to inhibition of water migration from one granule to another as the transition proceeded. The effect of gelatinization on the rheological properties of the composites also was investigated. Small-strain oscillatory measurements demonstrated that the native starch particles reinforced the gel matrix and that this reinforcement increased if the starch was gelatinized. However, under large deformation conditions, the native granules caused the stress and strain at failure to decrease. The gelatinized particles had the same effect at relatively low concentrations. The weakening of the gel was probably caused by stress concentrations, which lead to failure, in the vicinity of the granules. At relatively high-gelatinized starch concentrations the composite was strengthened. This may have been due to an increase in the adhesion between the filler and the gel combined with the depiction of the continuous phase of the solvent.
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