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 (P B), black bean (BE) and express field pea (FP) starches were heat-trea ted at 100 degrees C for 16h at a moisture content of 30%. The heat tr eatment did not change granule size and shape. The surfaces of GAP and EL were modified after heat treatment. Heat treatment decreased amylo se leaching (GAP > FP similar to EL > BB-PB) and the swelling factor ( EL similar to FP>GAP>BB similar to PB). The X-ray diffraction intensit ies increased in GAP starch, but decreased in the other starches (FP>B B>PB>EL). However, the X-ray pattern of all starches remained unchange d 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 te mperature (EL-EP>BB-PB). However, the gelatinization enthalpy (Delta H ) of all starches remained unchanged. The susceptibility towards hydro lysis by porcine pancreatic cr-amylase increased on heat treatment (BE > EL > FP > PB > GAP). The action of a-amylase on the starches decrea sed Delta H in EL and FP. However, Delta H decreased only marginally i n PB and BE. Acid hydrolysis (2.2 N HCl) increased on heat treatment ( BE > FP similar to EL similar to PB > GAP). The results showed that bo nding 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 t he starch source. (C) 1997 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology.