Comparative Investigation on Acid Hydrolysis of Sweet Potato Starches with Different Amylopectin Chain-Length

The solubilization of starch from the new sweet potato cultivar Quick Sweet (QS) in 2.2 M aqueous HCI occurred at a much higher rate than that from normal sweet potato (NS). QS starch has an abnormal amylopectin chain-length distribution with an unusually high percentage of short side-chains. Two-stage hydrolysis occurred in both cases. The apparent first-order kinetic constants (k) were calculated for both stages of the hydrolytic process in both types of sweet potato starch. A more drastic difference between the winvestigated starches (k for QS and INS starches was 27.0 x 10(-2) d(-1) and 7.0 x 10(-2) d(-1), respectively) was observed for the first stage of the hydrolysis affecting the amorphous regions of starches whereas the rate for the second stage (the degradation of the crystalline part) for the starch from OS was only slightly higher. The role of the structural defectiveness of QS in decreasing the granular resistance to acid hydrolysis and increasing the absorptive properties of the granules for water molecules is discussed.