PURIFICATION AND CHARACTERIZATION OF A NEUTRAL PROTEASE THAT CONTRIBUTES TO THE UNIQUE FLAVOR AND TEXTURE OF TOFU-MISOZUKE

Tofu-misozuke, a food inherent to the Fukuoka district of Japan is a t ype of soybean curd fermented in mise (soybean paste), possessing a un ique taste and texture. A cheese-like taste and softness also develops in Tofu-misozuke during ripening. The changes in Tofu-misozuke are ca used by proteases originating from Koji, one of the raw materials of m ise. We examined which of the proteases is the cause of taste and text ural-alterations. The protease was purified by DE52, Sephacryl S-300, Mono Q, and Superose 12 chromatography. The amino terminal sequence of the purified enzyme is TEVTDXKGDA, in agreement with the sequence of neutral protease II from Aspergillus oryzae. The purified enzyme is a heat stable metallo-protease. These results indicate that the purified enzyme is highly similar to the neutral protease II of Aspergillus or yzae.