Isolated rice starch fine structures and pasting properties changes during pre-germination of three Thai paddy (Oryza sativa L.) cultivars

Abstract

This research aimed to investigate fine structural changes and pasting properties of isolated rice starches during pre-germination. Three stages of pre-germinated brown rice (PGBR) and flour were prepared from three different Thai paddy cultivars. Changes in α-amylase activities of flour were determined. Starch was isolated from the flour by alkali extraction. The molecular size distributions, amylopectin branch chain length distributions, and pasting properties of three-stage PGBR starches were compared to ungerminated brown rice (UGBR) starches. During pre-germination, the α-amylase activities of PGBR flour from all rice cultivars were increased. Isolated UGBR starches from the three rice cultivars had higher starch yields than three-stage PGBR starches. HPSEC-RI results showed different molecular size distributions; the amylose contents of KDML105 and RD31were reduced from 15.5 to 12.7% and 18.6 to 15.8% at the 1st and 2nd stages of pre-germination, respectively. HPAEC-PAD results indicated that isolated three-stage PGBR starches from three rice cultivars had lower short A chains amylopectin branch chains than their UGBR starches. Pre-germination affected pasting properties in which the peak viscosities changed at the 1st stage of pre-germination for RD6 (3662 cP) and the 2nd stage of pre-germination for KDML105 (3860 cP) and RD31 (2279 cP) cultivars.