Kinetics of in situ and in vitro gelatinization of hard (T. durum) and soft (T. aestivum) wheat starches were investigated during cooking in water at 60degreesC, 70degreesC, 80degreesC, 90degreesC, and 100degreesC. At the given temperatures, the gelatinization process ceased before 100% completion at a final degree of gelatinization (FDG) for all starches. At the same temperature, the FDG was higher for the in vitro gelatinization than the in situ gelatinization for both hard and soft wheat starches. It was higher for the soft wheat starch than the hard wheat starch for both in situ and in vitro processes. Effect of temperature on the FDG was assessed through a Clausius-Clapeyron type equation. Starch gelatinization followed first-order reaction kinetics for both in situ and in vitro processes. The reaction rate constant (k(r)) was higher for the in vitro gelatinization than the in situ gelatinization for both starches. It was higher for the soft wheat starch than the hard wheat starch for both processes. The k(r) values were in the order of 10(-5) to 10(-4) s(-1) for the in situ gelatinizations and 10(-4) to 10(-3) s(-1) for the in vitro gelatinizations. The rate of the gelatinization reaction increased with increasing temperature and the effect of temperature on k(r) was evaluated using an Arrhenius type equation. In vitro gelatinizations had an average activation energy (E-a) of 76 kJ/mol between 60degreesC and 100degreesC. In situ gelatinizations had an average E-a of 137 below 75degreesC, and 79 kJ/mol above 75degreesC. Assuming the in vitro gelatinizations were effectively controlled by the reaction of starch with water between 60degreesC and 100degreesC, the in situ gelatinizations were effectively controlled by water transfer below 75degreesC and reaction of starch with water above 75degreesC. (C) 2002 Elsevier Science Ltd. All rights reserved.