A Preventative Process for Haze Formation in Shiro-shoyu using Protease

摘要

Shiro-shoyu is a type of soy sauce (shoyu) produced mainly from wheat. When raw shiro-shoyu is heated for pasteurization, the heated shiro-shoyu often clouds and produces sediment during storage. In order to prevent this phenomenon in typical shoyu such as koikuchi- and usukuchi-shoyu, raw shoyu is heated (hi-ire) to denature proteins, left to stand several days (on-sage) for flocculation, and then filtered to remove sediment. However, the conventional refinement procedures could not sufficiently clarify the heated shiro-shoyu. The haze formed in the hi-ire contained proteins. SDS-PAGE analysis revealed protein fragmentation, suggesting the activation of internal protease by heating. The residual haze present even after both the addition of a flocculant in the on-sage process and centrifugation was thought to gradually flocculate and eventually form secondary sediment. A commercially available protease was used in shiro-shoyu to produce a stable clarified product. Heat treatment to about 90 degrees C with 0.2% (w/v) or more of the protease significantly improved the clarity of shiro-shoyu after ori-sage and subsequent centrifugation. The addition of silica sal after heat treatment with the protease had the best effect on shiro-shoyu clarity. Nutrient composition of the treated shiro-shoyu was comparable to that of raw shiro-shoyu; however, heating resulted in slight darkening. When stored at 50 degrees C for 7 days, the treated shiro-shoyu maintained its clarity, while raw shiro-shoyu contained sediment. Thus, the protease treatment is a highly effective method for manufacturing clarified shiro-shoyu.