Modification of structural and physicochemical properties of cowpea (Vigna unguiculata) starch by hydrothermal and ultrasound treatments

Cowpea (Vigna unguiculata) starch was physically modified by heat moisture treatment (HMT) or HMT followed by ultrasound treatment (UST). The modifications of starch crystallinity, morphology and digestibility as well as thermal, and pasting characteristics were evaluated. HMT was performed at 20% moisture content, for 2, 5 and 12 h at 100 °C (HMT2, HMT5, HMT12). UST was performed at 80% amplitude (20 kHz) for 30 min (2 s on-2 s off). The granule shape and XRD patterns were not modified by any of the applied treatments. 1H NMR revealed that HMT and HMT-UST caused a decrease of amylopectin branching degree. Thermal stability increased more in heat-moisture-treated-starch, while gelatinization enthalpy was not affected by the treatments applied. The resistant starch content increased up to 11% with HMT, whereas an increase in slow digestible starch (SDS) (+30%) was observed in HMT2-UST and HMT5-UST. The decrease in pasting viscosity of treated starch samples increased incrementally with heating time. The results demonstrate that HMT and HMT-UST expand the opportunities and potential of using modified cowpea starches as ingredients in several food applications.