Structure and viscoelastic properties of starches separated from different legumes.

摘要

A comparison between the morphological, structural, thermal and viscoelastic properties of starches separated from pigeon pea, chick pea, field pea, kidney bean and black gram was made. The shape of the starch granules in the different legumes varied from oval to elliptical or spherical. X-ray diffraction of the legume starches indicated a typical C-pattern (mixture of A- and B-type). Granules of black gram and pigeon pea starch had a higher degree of crystallinity than those of field pea and kidney bean starches. Apparent amylose content of field pea, kidney bean, chickpea, blackgram and pigeon pea starch was 37.9, 36.0, 34.4-35.5, 32.9-35.6 and 31.8%, respectively. Distribution of isoamylase-branched materials among the starches revealed that proportions of long and short side chains of amylopectin were in the ranges 13.6-18.5 and 41.7-46.5%, respectively. Field pea and kidney bean starch had the highest apparent amylose contents and the lowest amounts of long side chains of amylopectin, respectively. Black gram and pigeon pea starch possessed higher proportions of both long and short side chains of amylopectin than field pea and chickpea starches. The onset, peak and conclusion temp. of gelatinization (To, Tp and Tc, respectively) were determined by DSC. To and Tc ranged from 59.3 to 77.3, 66.8 to 79.6, 55.4 to 67.6 and 68.3 to 69.3 degrees C, respectively, for chick pea, black gram, field pea and kidney bean starch. The enthalpy of gelatinization (Hgel) of field pea, kidney bean, chick pea, black gram and pigeon pea starches was 3.6, 3.0, 2.6-4.2, 1.6-1.7 and 2.6 J/g, respectively. Pastes of blackgram and pigeon pea starches showed lower storage and loss shear moduli than field pea, kidney bean and chick pea starches. The changes in moduli during 10 h at 10 degrees C revealed retrogradation in the order of: field pea > kidney bean > chickpea > blackgram > pigeon pea starch. In black gram and pigeon pea starches, the lower proportion of amylose plus intermediate fraction and higher proportion of short and long side chains of amylopectin are considered responsible for the higher crystallinity, gelatinization temp. and enthalpy of gelatinization.