Starch chain interactions within the amorphous and crystalline domains of pulse starches during heat-moisture treatment at different temperatures and their impact on physicochemical properties

Pulse (faba bean [FB], black bean [BB] and pinto bean [PB]) starches were heat-moisture treated (HMT) at 80, 100 and 120°C for 12h at a moisture content of ∼23%. Structural changes on HMT were monitored by microscopy, HPAEC-PAD, ATR-FTIR, WAXS, DSC and susceptibility towards acid and enzyme hydrolysis. Amylopectin chain length distribution remained unchanged in all starches on HMT. In all starches, HMT increased crystallinity and gelatinisation temperatures. The gelatinization enthalpy remained unchanged in some starches, whereas it decreased slightly in other starches on HMT. Slowly digestible starch content decreased at all temperatures of HMT, whereas resistant starch content increased at HMT80 and HMT100 (HMT80>HMT100), but decreased at HMT120. Birefringence, B-type crystallites and acid hydrolysis decreased on HMT. The extent of the above changes varied amongst starch sources and genotypes. HMT altered the X-ray pattern from A+B→A. The results of this study showed that structural reorganisation of starch chains during HMT temperature was influenced by starch chain flexibility, starch chain interactions and crystalline stability of the native granules.