Structural Properties of Amylopectins Corresponding to Physical Properties of Rice Starches Appropriate for Sake

Abstract

Starches from a variety of Sake-rice (Yamadanishiki, Gohyakumangoku, Miyamanishiki, Kitanishiki and Wakamizu) which are suitable for Sake brewing were investigated by comparing them with Koshihikari starch to recognize their structural properties of amylopectins. The partial hydrolysate (about 15% hy drolysis) of starch with isoamylase was fractionated into three fractions (fr.1, fr.2 and fr.3) by gel permeation chromatography (GPC) with a Toyopearl HW-50S, and then the short-amylose chains derived mainly from the outer portion of the amylopectin collected in the fr.3 were analyzed by a HPAEC-system equipped with a pulsed amperometric detector (HPAEC-PAD). From comparison of the chain-length distributions between Sake-rice starches and that of Koshihikari, it was found that Sake-rice amylopectins were plentiful in longish chains around DP 13-23 and scarce in shortish chains around DP 6-12, suggesting a structural property susceptible to retrogradation. The pasting properties of Sake-rice starches analyzed by Rapid Visco Analyzer (RVA) showed higher pasting temperature (PT), higher setback (SB), and lower breakdown (BD) than Koshi hikari starch, suggesting the outer portions of amylopectin had abundant longish debranched short side chains. These results suggested that rice starches with amylopectins susceptible to retrogradation are adequate for Sake-rice.