Mutants that have shorter amylopectin chains are promising materials for slow-hardening rice bread

Bread staling is a serious economic issue for the baking industry. Here, we found that shorter amylopectin chains caused by mutations play a role in maintaining the softer texture of rice bread. We used three rice cultivars that have a high proportion of short amylopectin chains in endosperm starch, two of which were starch branching enzyme I mutants, to make gluten-free and gluten-containing bread. Compression tests showed that the hardening rates for both types of bread made from these cultivars were markedly lower than those for control rice breads (gluten-free bread: 14%–39%, gluten-containing bread: 13%–27%), although there were no clear differences in the hardness values among the breads one day after baking. Sensory tests conducted two days after baking showed that gluten-free breads made from the three cultivars were softer than the control breads. Amylose contents, flour particle sizes, and damaged starch contents were similar among the flour samples, indicating that shorter amylopectin chains led to the slow-hardening of the rice bread. This finding can be applied not only to the breeding of rice cultivars for softer bread, but also to breeding of wheat and other cereals for bread.