Effects of Iron and Some Trace Metal Ions in Shoyu on the Increase of Color of Shoyu

Abstract

Effect of iron and other trace metals in Shoyu on the increase of color by oxidation and heating was examined. The results obtained were as follows; (1) Iron and the other trace metals were almost removed from shoyu by treatment with Dowex A-1 resin. (2) The color of the Shoyu treated with Dowex A-1 resin was apparently increased by oxidation, but the rate of the increase was smaller than that of the untreated Shoyu. (3) Fe2+ and Mn2+ mainly contribute to the increase of the color of Shoyu, while the other trace metal ions, Cu2+, Zn2+, Co2+, Ni2+, and Cd2+ did not. Unknown factors might also considerably conduce to the increase of color of Shoyu. (4) Iron ions (Fe2+, Fe3+) had no effect on the increase of color by heating. © 1970, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.