Ripening rice grains under low temperature for the high loaf volume and slow firming of gluten-free rice bread without additives

Abstract

Low specific volumes and high firming rates are major issues in the preparation of gluten-free rice bread. Herein, we discovered that flour acquired from rice grains ripened under lower temperatures improved the specific volume and firming rate of the resultant gluten- and additive-free rice bread. Two cultivars with different amylose contents were grown during three growing seasons (early, normal, and late) over two years (2016 and 2017). The temperatures during grain filling ranged from 22.0 to 30.1 °C, and the small differences observed between the average particle sizes and the damaged-starch contents of the samples indicated that their grain-filling temperatures had minimal influence on their flour properties. There were significant negative correlations between the grain-filling temperatures and the amylose contents or ratios of short amylopectin chains of the rice-flour samples. The bread loaf volumes were influenced by their amylose contents, not by their amylopectin structures, and correlated negatively with the grain-filling temperatures. Inversely, the bread-firming rates during storage were influenced predominantly by their amylopectin structures, and positively correlated with the grain-filling temperatures. These results indicate that rice grains ripened under lower temperatures are desirable, and that the grain-filling temperature can be an indicator of the firming of gluten-free rice bread.