Studies on the Activities of Bacteria in Soy Sauce Brewing

Abstract

The activity of proteinases in soy masy juice was measured by a modification of the Anson’s method. Compared to proteinases of purely cultured soy koji digest which consisted of only Aspergillus proteinases, no difference was observed with the proteinases of usual soy mash through the studies of pH-proteinese activity curves, the inhibition test, and inactivation by acid and alkali treatment. It is supposed, therefore, that the proteinases in soy mash are mostly of Aspergillus origin. Viable counts on salted media, heat shocking at 80°C for thirty minutes, and the microscopic counts proved that there are very few Bacilli vegetative cells in soy mash. From these facts the author assumed that Bacilli mainly grow in the koji and survive in the soy mash mostly in the form of spores. This work also suggested that the so-called “Aspergillus alkaline proteinase” consists of two distinct proteinases, and further the existence of an inhibitor which only acts at pH8. Thirteen strains of salt tolerant specific lactic acid bacteria were isolated from soy sauce brewing mashes, and their taxonomical characteristics investigated. These strains are spherically shaped, generally assume a tetrad form, micoaerophilic, and perform the homo-type fermentation. Eleven strains produce d-lactic and two other strains produce dl+(d) lactic acid. These characters are unaffected even when grown in salted broth containing 15% sodium chloride. They grow well in a medium containing 18% salt, and the upper limit of the salt tolerancy is approximately between 24 to 26% sodium chloride. The salt tolerant capacity seems to be a hereditable character. The strains grow within a pH range between 5.5 to 9.0, but no growth is observed at pH5.0. The optimal temperature was from 20°C~30°C. Many sugars are well fermented, and this ability was not diminished in 17% salted media. From these facts, the author proposed the name Pediococcus soyae nov, sp. for this sort of organism. This bacteria requires two specific nutrients: namely, a peptide-like substance (P-factor) included in the “Polypepton” (Takeda) and a dialyzable unknown substance (S-factor) included in the “Heart infusion broth”, “Yeast extract” and “Beef extract” (Difco). This bacteria do not require leucovorin.