Influence of high rainfall at the time of harvest on cassava starch properties
1997
Oates, C.G. | Santisopasri, V. | Kurotjanawong, K. | Petchalanuwat, C. | Sriroth, K. (National Univ. of Singapore, (Singapore). Dept. of Biochemistry)
Five commercially important cultivars, Rayong 1, Rayong 5, Rayong 60, Rayong 90 and Kasetsart 50 were tested to determine the most suitable harvesting time from early (6 months) to late (16 months) harvest. Drought conditions prevailed during months 7 through to 11 with heavy precipitation in the remaining months of the trial. Starch structure characteristica, known to be correlated to rainfall in the four weeks prior to harvest, were evaluated. Starch extracted from cassava harvested in the late period, during the rainy season, was structurally different to that extracted prior to the onset of the rainy season. Common to starches from all cultivars, apparent size of amylose was larger in samples extracted during months 14 and 16, prior to this there was little variation in amylose size. The shift to apparently higher molecular weight amylose was most apparent in Rayong 60, a cultivar developed for early harvest. Apparent amylose content also changed with time of harvest, during the later months (14 and 16) the proportion of this macromolecule fraction was reduced. Despite and apparent lack of relationship between precipitation and granule crystallinity, as measured by enthalpy of gelatinisation, the nature of the crystalline material changed with harvest time. This was expressed by development of two populations of crystalline material in samples harvested during the final two months of the trial. Morphological changes in granule structure were also noted. These results may represent either the influence of moist conditions during harvest on accelerated deterioration post harvest, or as a consequences of starch mobilization post drought as the plant increases the surface foliage cover.
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