Effect of heat—moisture treatment on the structure and physicochemical properties of legume starches

Native green arrow pea (GAP), eston lentil (EL), othello pinto bean (PB), black bean (BB) and express field pea (FP) starches were heat-treated at 100 °C for 16 h at a moisture content of 30%. The heat treatment did not change granule size and shape. The surfaces of GAP and EL were modified after heat treatment. Heat treatment decreased amylose leaching (GAP > FP~EL > BB~PB) and the swelling factor (EL ~ FP > GAP > BB ~ PB). The X-ray diffraction intensities increased in GAP starch, but decreased in the other starches (FP > BB > PB > EL). However, the X-ray pattern of all starches remained unchanged after heat treatment. Differential scanning calorimetry of the heat-treated samples showed a broadening of the gelatinization temperature range and a shifting of the endothermal transition towards a higher temperature (EL-EP>BB-PB). However, the gelatinization enthalpy (ΔH) of all starches remained unchanged. The susceptibility towards hydrolysis by porcine pancreatic α-amylase increased on heat treatment (BB > EL > FP > PB > GAP). The action of α-amylase on the starches decreased ΔH in EL and FP. However, ΔH decreased only marginally in PB and BB. Acid hydrolysis (2.2 N HCl) increased on heat treatment (BB>FP~EL~PB>GAP). The results showed that bonding forces within the amorphous regions of the granule, crystallite orientation and the granule surface (in GAP and EL) are altered during heat treatment, the magnitude of these changes being dependent upon the starch source.