Effect of thermal processing and storage on digestibility of starch in whole wheat grains

Gelatinisation and retrogradation of starch in wheat flour systems and whole wheat grains were studied using differential scanning calorimetry (DSC) and the impact of these events on starch digestibility was investigated. Retrogradation of starch was studied with partially and fully cooked (boiled at 100°C for 12 min and 32 min, respectively) wheat grains that were subjected to storage at 22°C for 48 h. Stored samples had lower digestibility values when compared to the freshly cooked counterparts. The effect of moisture on retrogradation was studied with fully cooked wheat grains that were dried to a range of moisture contents (14.6 to 35.9%, wwb) and stored at 20°C for 24 h. The retrogradation enthalpy increased with increasing moisture content. The possibility of estimating the degree of retrogradation in fully cooked grains (32 min cooking) was investigated using a wheat flour-water system. The retrogradation enthalpy of the fully cooked grains was slightly higher than the wheat flour-water system (at a moisture content of 49%, wwb) during the course of storage at 22°C.