STUDIES ON THE PROPERTIES OF STARCH OF DIPLOID IPOMOEA-TRIFIDA (HBK) DON STRAINS

Starches of six diploid Ipomoea trifida (H. B. K.) DON. clonal strains were examined. Granule size, granule traits obtained by scanning electron microscopy (SEM), X-ray diffraction patterns and differential scanning calorimetry (DSC) parameters of starches of the diploid strains were compared with those of two sweet potato cultivars. The granule sizes of the diploids were definitely smaller than those of cultivars. SEM showed that starches of the diploid strains were composed of predominantly angular granules having crater-like impressions. Starches of both the diploids and the cultivars showed typical X-ray diffraction patterns (C type) with diffuse maximum peak around 18.5-degrees 2theta, but in the case of diploid strain ''H3-28'', distinctive sharp peaks suggesting some differences in crystal structure were observed. DSC parameters, namely, onset temperature (To), peak temperature (Tp), conclusion temperature (Tc) and enthalpy of gelatinization (DELTAH) obtained from starch-water mixtures (ratio 1:3) were higher in the diploid starches compared to those of the two cultivars. Significant correlation coefficients were found between the gelatinization parameters and mean granule diameter of the starches studied.