Densely packed-matrices of heat moisture treated-starch determine the digestion rate constant as revealed by logarithm of slope plots.

Factors affecting the extent and rate constant of starch digestion have been determined by applying logarithm of slope (LOS) plot approach to banana starch modified by heat moisture treatment (HMT) at different temperatures (100, 110 and 120 °C) and time (4 and 8 h). LOS plot result showed that native and HMT-starches exhibited two separate digestion rate constants (k 1 in rapid and k 2 in slower phase). The digestibility increased with the increase in temperature and time of HMT in which the amount of digestible starch at slower phase (C 2∞ ) predominantly contributed to the increase in total digestible starch (total C ∞ ). Small change of the digestible starch in rapid phase (C 1∞ ) might be attributed to the comparatively intact granule surfaces and the relatively small change in ratio of ordered to disordered α-glucan chains at the granule surface as observed by FTIR-ATR. Meanwhile the increase in C 2∞ might be linked to the decrease in crystallinity as observed by XRD. Compared to the native starch, denser packed-structure characterising an A-type crystalline structure in HMT-starches is a key factor determining the lower k 2 in HMT-starches. The densely packed-matrices might slow down the amylase diffusion through the granule to reach digestible α-glucan chains. © Association of Food Scientists & Technologists (India) 2020.