Translocation of Barley β-amylase into Rice Grains during Cooking Rice Mixed with Barley (Mugimeshi)

Abstract

Cooking rice mixed with barley, called Mugimeshi in Japanese, is one of the most common multi-grain cooking styles in Japan. While the localization and functions of rice starch-degrading enzymes such as α- and β-amylases during rice cooking have been well studied, those of barley enzymes remain unknown—especially when barley is cooked with rice. In this study, we investigated the localization of barley β-amylase using an immunoblot technique when barley and rice were soaked in water and heated together to 60°C. Surprisingly, barley β-amylase was found not only in barley grains and cooking water, but also in rice grains after barley and rice were soaked in water for one hour. In rice grains, the amount of barley β-amylase was highest when the water temperature reached 40°C. These data clearly showed that some barley β-amylase was translocated from barley grains into rice grains through the cooking water. The finding raises the possibility that in addition to rice enzymes, barley β-amylase contributes to rice starch degradation during Mugimeshi cooking.