Kinetic study of the retrogradation of gelatinised starch

Abstract

Abstract A method was developed for the study of starch retrogradation by differential thermal analysis. The kinetics of the crystallisation process were studied using the expression θ8 = exp (‐ kt n ), where θ = the fraction of crystallisable starch remaining uncrystallised at time t. The values for the Avrami exponent ( n ) and the rate constant ( k ) were found to coincide with values previously obtained for the staling of bread, as followed by measurement of crumb elastic modulus. No difference between the time constants of gels cooled slowly and rapidly after gelatinisation was found, indicating that the nucleation process in starch crystallisation is instantaneous in the systems studied. The fact that the Avrami exponent is unity also suggests that the nucleation process is instantaneous, and that it is followed by rod‐like growth of crystals.