Effects of amylosucrase treatment on molecular structure and digestion resistance of pre-gelatinised rice and barley starches.

Structural modification of rice and barley starches with Neisseria polysaccharea amylosucrase (NpAS) was conducted, and relationship between structural characteristics and resistant starch (RS) contents of NpAS-treated starches was investigated. Pre-gelatinised rice and barley starches were treated with NpAS. NpAS-treated starches were characterised with respect to morphology, X-ray diffraction pattern, amylopectin branch-chain distribution, and RS content, and their structural characteristics were correlated to RS contents. Regardless of amylose contents of native starches, NpAS-treated (relative to native) starches possessed lower and higher proportions of shorter (DP 6-12) and intermediate (DP 13-36) amylopectin (AP) branch-chains, respectively. RS contents were higher for NpAS-treated starches relative to native starches, and maximum RS contents were obtained for NpAS-treated starches of waxy rice and barley genotypes. Amylose contents were not associated with RS contents of NpAS-treated starches. However, shorter and intermediate AP branch-chain portions were negatively and positively correlated to RS contents of NpAS-treated starches, respectively.