Banana starch modified by heat moisture treatment and annealing: Study on digestion kinetics and enzyme affinity

Starch modification by annealing (ANN) and heat-moisture treatment (HMT) results in a lower crystallinity compared to native but the change of B crystalline type to A type is only observed in HMT starch. All starches possess two different digestion rate constants i.e. k1 (at rapid phase) and k2 (at slow phase) which may be linked to the preserved intact starch granule following thermal treatment. HMT starch contains higher content of slowly digestible starch (C-2 infinity) compared to the C-2 infinity of the other starches. The lower enzyme binding to HMT starch (Kd value increases from 0.12 mg/mL in native starch to 0.83 mg/mL) may be linked to the increase in the degree of ordered structure of the granule surface (observed from the absorption band ratio of 1000 cm(-1)/1022 cm(-1)). The lower affinity may lead to a lower k1 value. This holds true for ANN and native starch which displays similar k(1), Kd value and degree of ordered to disordered structure. Lower k(2) in HMT starch compared to the corresponding k(2) in the other starches may be linked to the slower enzyme diffusion into the core of starch granule due to the tightly packed structure of A crystalline type in HMT starch.