Vitamin B-12 production in soybean fermentation for tempeh

Most studies have found that vitamin B12 in tempeh is produced by contaminating bacteria specifically, Klebsiella sp. and Citrobacter freundii, during fungal fermentation. This study is to evaluate the effect of starter culture on the vitamin B 12 and isoflavone aglicone content of soybean fermentation for tempeh production. In this study, soybeans were washed, soaked in water overnight, dehulled and sterilized by boiling at 100 degrees C for 30 min. Three starter cultures (10(3) CFU g(-1)) namely Rhizopus oligosporus, Klebsiella sp. and Saccharomyces cerevisiae were then inoculated as follows, soybeans + R. oligosporus + Klebsiella sp. (SRK), soybeans + R. oligosporus + S. cerevisiae (SRSc), soybeans + R. oligosporus + S. cerevisiae + Klebsiella sp. (SRScK), and Soy + R. oligosporus (SR) and soybeans + Klebsiella sp (SK). Inoculated soybeans were then incubated at 30 +/- 2 degrees C for 40 hours (tempeh-style). The growth of Klebsiella sp., S. cerevisiae, R. oligosporus and the production of vitamin B-12 as well as isoflavone aglicones were observed. The results showed the highest vitamin B-12 3.15 mg 100 g(-1) was found in tempeh SRSc, followed by 2.88 mg 100 g(-1) and 1.64 mg 100 g(-1) in tempeh SR and SRScK, respectively. In addition, vitamin B12 in tempeh SRK was the lowest (0.81 mg 100 g(-1)). All the starter cultures were able to hydrolyze daidzin and genistin, but the amount of daidzein and genistein was tripled and doubled, respectively when Klebsiella sp was inoculated to the soybean fermentation. The study suggested that S. cerevisiae contributes to the production of vitamin B-12, while Klebsiella sp contributes to production of daidzein and genistein in soybean fermentation for tempeh production.