Combined effects of planting and harvesting dates on starch properties of sweet potato roots

Starch was extracted from sweet potato roots differing in planting and harvesting dates. The physicochemical properties of the isolated starches were analyzed. Amylose content was found to be almost independent of both planting and harvesting dates. The proportions of the short chains of amylopectin were lower at the earliest harvesting, while the planting date had little influence on the chain length distribution of amylopectin. Not only the harvesting date but also the planting date were confirmed to have a profound effect on pasting and gelatinization properties determined by rapid viscoanalyzer (RVA) and differential scanning calorimetry (DSC), respectively. Earlier planting and harvesting apparently enhanced the onset and peak temperatures for gelatinization determined by DSC and the pasting temperature determined by RVA. Furthermore, earlier planting and harvesting dates were generally associated with lower peak viscosity determined by RVA. The effect of planting and harvesting dates on the mean size of starch granules, starch granule digestibility by glucoamylases and X-ray diffractograms of starch was also investigated. (C) 1997 Elsevier Science Ltd.