Vitamin B<sub>12</sub> production in soybean fermentation for tempeh
Maria Erna Kustyawati, Subeki Subeki, Murhadi, Samsul Rizal, Penipuji Astuti
Abstract
Most studies have found that vitamin B<sub>12</sub> in tempeh is produced by contaminating bacteria specifically, <em>Klebsiella</em> sp<em>.</em> and <em>Citrobacter freundii,</em> during fungal fermentation. This study is to evaluate the effect of starter culture on the vitamin B<sub>12</sub> 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 ℃ for 30 min. Three starter cultures (10<sup>3</sup> CFU g<sup>-1</sup>) namely <em>Rhizopus oligosporus, Klebsiella</em> sp. and <em>Saccharomyces cerevisiae</em> were then inoculated as follows, soybeans + <em>R. oligosporus</em> + <em>Klebsiella</em> sp. (SRK), soybeans <em>+ R. oligosporus</em> + <em>S. cerevisiae</em> (SRSc), soybeans + <em>R. oligosporus</em> + <em>S. cerevisiae</em> + <em>Klebsiella</em> sp<em>.</em> (SRScK), and Soy + <em>R. oligosporus</em> (SR) and soybeans + <em>Klebsiella sp</em> (SK). Inoculated soybeans were then incubated at 30 ±2 ℃ for 40 hours (<em>tempeh</em>-style). The growth of <em>Klebsiella</em> sp., <em>S. cerevisiae, R. oligosporus</em> and the production of vitamin B<sub>12</sub> as well as isoflavone aglicones were observed. The results showed the highest vitamin B<sub>12</sub> 3.15 mg 100 g<sup>-1</sup> was found in tempeh SRSc, followed by 2.88 mg 100 g<sup>-1</sup> and 1.64 mg 100 g<sup>-1</sup> in tempeh SR and SRScK, respectively. In addition, vitamin B<sub>12</sub> in tempeh SRK was the lowest (0.81 mg 100 g<sup>-1</sup>). All the starter cultures were able to hydrolyze daidzin and genistin, but the amount of daidzein and genistein was tripled and doubled, respectively when <em>Klebsiella sp</em> was inoculated to the soybean fermentation. The study suggested that <em>S. cerevisiae</em> contributes to the production of vitamin B<sub>12</sub>, while <em>Klebsiella sp</em> contributes to production of daidzein and genistein in soybean fermentation for tempeh production.