Changes in physicochemical properties and morphology of canna starches during rhizomal development

Abstract
Canna rhizomes aged seven months were harvested, and their segments were classified into four groups: mother, immature, premature and mature segments, according to the sequence of development. Based on weight of the segments, the mature segment was the greatest part (70%), whereas the immature and premature were of comparable amounts (14% and 15%, respectively). The average weight of one rhizome was 5324 g. Starch content increased from the immature segment (13.7%) to the premature segment (19.5%), and slightly decreased in the mature segment (18.6%), while the mother segment had the lowest starch content (7.9%). The size of the starch granules increased with progressive development of segments from immature to premature and mature stages. Starch from the mother segment contained a higher proportion of small size granules than the other segments and unusual features were observed on the surface of some granules. The appearance of granules from the different samples subjected to the same period of hydrolysis by porcine pancreatic α-amylase was similar, although differences in the degree of hydrolysis were found. Signs of degradation were more readily seen as the period of hydrolysis was extended. The mode of attack by α-amylase on canna starch was principally digestion through surface corrosion. Starches from different segments showed similar crystalline structures, and thermal and pasting properties; however, some aspects of the chemical composition of starch from the mother segment were different from the others.