Decolorization of Japanese soy sauce (shoyu) using adsorption Original Research Article

A systemic adsorption study was conducted to find an appropriate process to decolorize Japanese soy sauce (shoyu) without changing the sensory quality, using activated carbon (AC), activated clay (ACL), diatomaceous earth (DE), magnesium oxide (MGO), and silica gel (SG). The AC, ACL, and SG processes exhibited decolorizing ability, but the DE and MGO processes did not. The decolorizing ability of AC was 30 times that of ACL, at the same time the decolorizing ability of ACL was 3 times that of SG. AC-, ACL-, and SG-processed soy sauces had similar characteristic curves in plots of Δa∗ against Δb∗ and ΔC∗ against ΔL∗. When the decolorizing degree was the same, a major quality index (e.g., total nitrogen (TN), unsalted soluble solid content (USSC), ethanol, and pH) was maintained with AC but not with ACL (especially pH), while SG maintained the quality index except for ethanol. AC and SG did not reduce amino acids or organic acids (e.g., lactic acid and acetic acid), indicating contained sensory quality.