Prevention of haze formation in shiro‐shoyu using silica gel

An adsorption technique was employed to remove the haze‐causing proteins from shiro‐shoyu , a type of soy sauce. Protein content in shiro‐shoyu was reduced by incubation with silica gel. The removal of protein was dependent on the incubation temperature. At the optimal temperature of 60°C, the protein removal exceeded 80% of the total protein content. SDS‐PAGE pattern analysis of shiro‐shoyu and western blotting analysis with anti‐α‐amylase antibody suggested that the thermal denaturation of proteins and proteolytic degradation by endogenous proteases in shiro‐shoyu facilitated efficient protein adsorption onto silica gel by increasing the hydrophobicity of protein molecules. Physical and chemical properties of the silica gel‐treated shiro‐shoyu were comparable to those of raw shiro‐shoyu except for the decrease in protein content. When stored at 50°C for 7 days, shiro‐shoyu heated for pasteurization after silica gel treatment kept its clarity, whereas shiro‐shoyu heated without silica gel and raw shiro‐shoyu contained sediment. Practical Applications Shoyu (soy sauce) is a traditional Japanese seasoning brewed from soybeans, wheat, shoyu ‐ koji mold, and salt water. When raw (unheated) shoyu is heated for pasteurization, it often becomes cloudy and produces sediment during storage. This haze phenomenon, derived from the aggregation of proteins, has led to customer complaints. It has been demonstrated that the haze arising from heating the raw shoyu can be clarified by removing sediments through the addition of flocculating agents such as silica sol. However, this conventional method is not suitable for clarifying heated shiro‐shoyu , which is a type of soy sauce ( shoyu ) made mainly from wheat. An adsorption technique using silica gel would be a very effective approach for manufacturing clarified shiro‐shoyu . The method would allow shiro‐shoyu to remain clear after pasteurization and prevent any haze or sediment formation during storage.