STUDIES ON THE PHYSICOCHEMICAL PROPERTIES OF NATIVE, DEFATTED, AND HEAT MOISTURE TREATED PIGEON PEA (CAJANUS-CAJAN L) STARCH

Starch from pigeon pea (Cajanus cajan L) was isolated and some of the important characteristics determined. The yield of starch was 29.7% on a whole seed basis. The shape of the starch granule was oval to elliptical to irregular, with granules 8-32 mum in diameter. Scanning electron micrographs revealed the presence of smooth surfaces with a large number of grooves. The gelatinization temperature-range was 347-354-360 K and the total amylose content was 29.3%, of which 2.7% was complexed by native lipids. The starch exhibited a restricted two-stage swelling pattern and a moderate solubility in water. The viscoamylographic examination of the starch paste (6% w/v) showed the absence of a peak viscosity, a low 95-degrees-C viscosity (80 Brabender units, BU) and an increase in consistency (140 BU) during the holding cycle at 95-degrees. Native granules were very resistance to hydrolysis by porcine pancreatic alpha amylase and 2.2 M HCl. The X-ray diffraction pattern was of the C-type. The results showed that the starch chains in the amorphous regions of pigeon pea were more highly associated than those of other legume starches. Defatting (hot 3:1 1-propanol-water) and heat-moisture treatment (100-degrees-C, 16 h, 30% moisture) increased the gelatinization temperature and broadened the gelatinization temperature range, with relatively little change in gelatinization enthalpy. Defatting and heat-moisture treatment also increased the pasting temperature and susceptibility towards alpha-amylase, but decreased the swelling factor, amylose leaching, and paste consistencies at 95 and 50-degrees-C. However, the relative crystallinity remained unchanged. Acid hydrolysis increased on defatting but decreased on heat-moisture treatment. Defatting caused greater changes to the granular surface than heat-moisture treatment.