Abstract
Generally, the microorganism involved in soybean fermentation for the production of tempeh is Rhizopus oligosporus. However, Saccharomyces cerevisiae, a type of β-glucan-producing yeast, is known to be present and grow in the fermentation process. This study was aimed at investigating yeast and fungal growth dynamics, β-glucan formation, and antibacterial activity against Escherichia coli during the fermentation after adding S. cerevisiae as an inoculum. The Randomized Complete Block Design (RCBD) was applied with two treatments and three repetitions. Three types of starter culture were S. cerevisiae, R. oligosporus, and the combination of both. The second treatment was fermentation time at room temperature (30 ± 2°C) for 0, 8, 16, 24, 32, and 40 hours. The dynamics were observed every eight hours. The obtained data were tested using Tukey's Honestly Significant Difference (HSD) test. The results indicated that yeast grew during this process from a single S. cerevisiae culture and a mixture of R. oligosporus and S. cerevisiae, but not from R. oligosporus alone. The yeast grew during and until the end of fermentation and decreased after 32 hours in the mixed cultures. The β-glucan formed in tempeh with all types of inoculum, but the antimicrobial activity against E. coli increased with fermentation time and was significantly different between treatments. The highest β-glucan content and antibacterial activity of tempeh are from the mixed culture. In conclusion, the addition of S. cerevisiae and R. oligosporus in soybean fermentation produced tempeh with the highest β-glucan content and antibacterial activity against E. coli. The presence of β-glucans suggests higher health benefits of tempeh.
Highlights
Tempeh is a traditional Indonesian fermented food produced from soybeans by using Rhizopus sp
This study used pure cultures of R. oligosporus FNCC 6010, S. cerevisiae FNCC 3012, and E. coli obtained from the UGM Inter-University Food and Nutrition Center, soybeans, Nutrient Broth (NB), Nutrient Agar (NA), Malt Extract Agar (MEA), and Potato Dextrose Agar (PDA)
During fermentation of soybeans with only the R. oligosporus culture, there was no increase in the amount of yeast (Figure 1(a)), whereas during fermentation using only S. cerevisiae alone, the fungus did not grow (Figure 1(b))
Summary
Tempeh is a traditional Indonesian fermented food produced from soybeans by using Rhizopus sp. This healthy functional food is due to bioactive compounds such as isoflavones. It has nutritional advantages, unique texture, and pleasant flavors [1]. The quality of tempeh depends on the raw material and type of inoculum or starter culture used. The kind of inoculum plays a vital role in making tempeh because it affects tempeh’s quality. Tempeh uses an inoculum containing R. oligosporus [2]. Other important microorganisms involved in fermenting soybeans to form tempeh are R. oryzae and R. stolonifer [3]. All three microorganisms ferment soybeans into tempeh. R. oligosporus synthesizes more protease enzyme, whereas R. oryzae favors the α-amylase enzyme [5]
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