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∞) compared to the C_2∞ of the other starches. The lower enzyme binding to HMT starch (K_d 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 k₁, K_d value and degree of ordered to disordered structure. Lower k₂ in HMT starch compared to the corresponding k₂ 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.