Physicochemical properties of waxy rice varieties with contrasting hardening rates

Abstract

ABSTRACTIn the present study, four waxy rice varieties (two japonica and two indica) with contrasting hardening rates were used for physicochemical properties investigation. The results showed that the hardness of cooked rice grains from zhenzhunuo and zhennuo29 increased slowly after cool storage, whereas those from zaonuo5 and yj98 raised rapidly. The peak gelatinisation temperatures for yj98, zaonuo5, zhennuo29, and zhenzhunuo flours were 78.60°C, 73.55°C, 69.00°C, and 67.25°C, respectively. The retrogradation enthalpies of stored flours (4°C, 48 h) followed the order: yj98 (3.876 J/g) > zaonuo5 (2.202 J/g) > zhennuo29 (1.684 J/g) > zhenzhunuo (1.370 J/g). Scanning electron microscopy (SEM) results exhibited that after cool storage, the cooked rice grains of zhenzhunuo and zhennuo29 had no obvious changes in morphology, whereas zaonuo5 presented increased cavities and yj98 occurred new fissures. Among intra-subspecies varieties, the rapid hardening rice accessions had a lower ratio of A chains (DP 6–12) but larger proportion of B3 chains (DP ≥ 37) than that of the corresponding genotypes with slow hardening. The physicochemical characteristics disclosed here will facilitate the application of the four cultivars in food processing industry.

Keywords

• Amylopectin
• chain-length distribution
• hardness
• retrogradation
• waxy rice