Modeling the limited degree of starch gelatinization

The kinetics of starch gelatinization is usually described as a first-order reaction, that is, the rate of formation of gelatinized mass is assumed to be proportional to the unreacted amount. It is also assumed that the proportional constant, the reaction rate (k), has an Arrhenius-type dependence on temperature. The equation derived from this model predicts that all the starch eventually gelatinizes at any given temperature for any k different from zero. However, it is well known that gelatinization only initiates above the so called “gelatinization temperature.” In this study it is employed an alternative model that properly describes the actual experimental behavior, which deviates considerably from the first-order model prediction. The model introduces an empirical parameter that quantifies the extent of gelatinization when a starch-water mixture is held at certain temperature for “long enough.” The gelatinization degree was evaluated by applying thermal treatments to 70% moisture-content samples for 0, 0.5, 1, 3, 5, 7, and 10 min at several temperatures (61, 63, 65, 67, and 69°C). The gelatinization activation energy (E_A) derived from the alternative model is 176 ± 10 kJ/mol. Since the proposed model closely reproduces the experimental behavior, it is suggested that this value better describes the actual process. The proposed model allows for the proper modeling of the starch-gelatinization kinetics, which is relevant in starch gelatinization studies and in food processing industry.