Effects of reaction condition on glycosidic linkage structure, physical-chemical properties and in vitro digestibility of pyrodextrins prepared from native waxy maize starch

Glycosidic linkage structure, physical-chemical properties and in vitro digestibility of pyrodextrins prepared using different reaction conditions were characterized. Intensification of reaction condition promoted starch hydrolysis and transglucosidation until the solubility of pyrodextrin reached 100%. New branch points were formed including alpha-1,2, beta-1,2, beta-1,4, beta-1,6 and alpha-1,6 linkages. Majority of the branch points was alpha-1,6 and beta-1,6 linkages which in together accounted for more than 70% of the total branches. The degree of branching increased at intensified reaction conditions and plateaued at approximately 24%. Exhaustively hydrolyzing pyrodextrin by alpha-amylase and amyloglucosidase significantly decreased the degree of alpha-1,4 but not alpha-1,6 linkages. The retained alpha-1,4 and alpha-1,6 linkages were probably protected from enzyme hydrolysis by the non-starch linkages due to steric hindrance. The resistant starch content was positively correlated with the degree of branching of pyrodextrin. The decreased in vitro digestibility of pyrodextrin was attributed to the formation of new glycosidic linkages.