Involvement of Bacillus subtilis var. natto in Formation of 2,5-Dimethylpyrazine and 2,3,5-Trimethylpyrazine in Natto

Abstract

  Pyrazines, which are known as reaction flavors, are in natto. Bacillus subtilis var. natto (I) seems to be involved in the formation of pyrazines, although the formation mechanism is unclear. In this study, we showed that B. natto is involved in the formation of 2,5-dimethylpyrazine (II) and trimethylpyrazine (III), which are the major pyrazines of natto. The amounts of DMP and TMP increased significantly when autoclaved natto samples inoculated with natto were incubated at 37℃. Next, steamed soybean was inoculated with each of four strains of I. The pyrazines were detected after 24-48 h of incubation, and their amounts increased even 72 h after incubation. Further, we examined the effect of various components such as peptone, dicarbonyls, amino acids, etc. on the pyrazine formation using a minimal medium. Pyrazines were definitely detected only when threonine was added. It is suggested that II and III in natto are produced as secondary metabolites through the metabolism of threonine.