Adjacent double branches exist in the branching structure of starch.

Starch is composed of two giant polymers of glucose-linked amylose and amylopectin but is not considered to have a branched structure with adjacent α-1,6-linkages (adjacent double branches). We previously discovered that the oligosaccharide DP6-1 contains adjacent double branches in sake, a Japanese rice wine. In this study, we analyzed the oligosaccharides generated from rice starch following porcine pancreatic α-amylase and glucoamylase digestion by hydrophilic interaction chromatography coupled with time-of-flight/mass spectrometry. We found that their elution times were identical to those of the oligosaccharides containing adjacent double branches observed in sake. Nuclear magnetic resonance (NMR) analysis confirmed that one of the oligosaccharides was identical to DP6-1. This indicates for the first time that adjacent double branches exist in the branching structure of starch. The adjacent double branches were estimated to be present at a ratio of approximately 1:100 of the total branching points in rice starch, suggesting that the contribution of...