Improvement in gluten-free rice bread quality by protease treatment

• Protease treatment improved the quality of gluten-free rice bread.
• Loaf volume was increased and crumb hardness was decreased by the treatment.
• Well-aerated and many-cellular structures were observed in the crumb.
• Staling rate of the bread was lowered by the treatment.
• Protease digested preferentially non-protein body proteins of rice proteins.

The wide prevalence of gluten-related disorders has led to increase in the demand for gluten-free foods. Rice is a gluten-free and less allergenic cereal. However, bread made from rice flour, i.e., gluten-free rice bread, is generally of poor quality because rice flour cannot develop a network with gluten-like properties. In this study, we investigated the effects of protease treatment on gluten-free rice to improve the quality of its bread. Bread treated with a commercial protease from Bacillus stearothermophilus (thermoase) was of higher quality, i.e., good crumb appearance, high volume, and soft texture, depending on the amount of enzyme added. Rice proteins in the protease-treated bread were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which showed that glutelins and prolamins were hardly digested by thermoase in comparison with other proteins. Scanning electron microscopy revealed that many cellular structures were formed in the thermoase-treated bread; however, these structures were rare in the untreated control. Bread crumb color was not affected by the treatment. The staling rate was much lower for the thermoase-treated bread than for the control. These results indicate that thermoase treatment can be successfully used to improve the quality of gluten-free rice bread by partial digestion of rice proteins.