Effect of heat treatment on moisture sorption behavior of wheat flours using a hygrometric technique

Abstract

The water sorption isotherms of wheat flour were constructed at 30°C using a hygrometric (Novasina) method. Flour samples were preequilibrated to a w values of 0.22, 0.46, 0.57 and 0.75 and heat treated at 100°C for 0, 1 and 2 hrs to study possible changes in water sorption behavior induced by the heat treatment. Results showed that the sorption behavior of the flour was dependent both on time of heat treatment and amount of moisture present during heat treatment. At low water activity values heat treatment did not significantly affect the water sorption behavior of the flour. At higher water activity values (>=0.75) a reduction of 21.95% and 41.46% in water uptake was observed after 1 and 2 hrs of heat treatment respectively. These differences were attributed to (a) structural changes in wheat flour proteins (denaturation, crosslinking, coaggregation (b) phase transitions in the starch including annealing, recrystallization and amylose depolymerization and (c) formation of amylopectin-lipid complexes resulting in reduced water holding capacity of the flour.