Translocation of Rice α-glucosidase into Barley Grains while Cooking Rice Mixed with Barley (Mugimeshi)

Cooking rice mixed with barley, called Mugimeshi in Japanese, is one of the most common multi-grain cooking styles in Japan. While we reported the localization of barley beta-amylases during Mugimeshi cooking, that of rice enzymes remains unknown. In this study, we investigated the localization of rice alpha-glucosidase using an immunoblot technique while barley and rice were soaked in water and heated together to 60 degrees C. Surprisingly, rice alpha-glucosidase of Koshihikari cultivar was found not only in rice grains and cooking water, but also in barley grains after barley and rice were soaked in water for an hour. Rice alpha-glucosidase of Nipponbare cultivar was, however, not released from rice grains into cooking water. In barley grains, the amount of rice alpha-glucosidase from Koshihikari was highest after the soaking step. These data clearly showed that rice alpha-glucosidase was translocated from rice grains into barley grains via cooking water during Mugimeshi cooking in some rice cultivars. This finding suggests that, in addition to barley enzymes, rice alpha-glucosidase contributes to barley starch degradation during Mugimeshi cooking.