Abstract
Tempeh is traditionally produced by fermenting soybean with the fungus Rhizopus oligosporus found in banana leafs. We wanted to investigate if Taiwan’s flavorful red bean could be used as a healthy substitute for soybeans in tempeh. One bioactive component of tempeh is γ-Aminobutyric acid (GABA). We measured GABA content and shelf-life-related antimicrobial activity in red-bean tempeh made with four strains of Rhizopus, one purchased strain of Rhizopus, and an experimental co-cultured group (Rhizopus and Lactobacillus rhamnosus BCRC16000) as well as cortisol in red-bean-tempeh-treated zebrafish. GABA was highest in the co-culture group (19.028 ± 1.831 g kg−1), followed by screened Strain 1, the purchased strain, and screened Strain 4. All strains had antibacterial activity on S. aureus and B. cereus. The extract significantly reduced cortisol in zebrafish. However, Strain 1, with less GABA than some of the other strains, had the best effect on cortisol level, suggesting that other components in red-bean tempeh may also affect stress-related cortisol. We found the benefits of red-bean tempeh to be similar to those reported for soybean-produced tempeh, suggesting that it could be produced as an alternative product. Considering the Taiwanese appreciation of the red-bean flavor, it might find a welcoming market.
Highlights
The red bean (Phaseolus vulgaris) is an herbaceous annual plant of the family leguminosae [1]
R. microsporus var. oligosporus IFO 8631 Reverse Osmosis (RO) (ATCC 22959) fungus strains and Lactobacillus rhamnosus BCRC 16000, Escherichia coli BCRC 10239, Staphylococcus aureus BCRC 10451, and Bacillus cereus BCRC 10927 bacteria were obtained from the Bioresource Collection Research Center (BCRC), Food Industry Research and Development Institute (Hsinchu, Taiwan)
Following sterilization at 120 ◦C for 20 min, the mixture was poured into a Petri dish and test tube, and cultured in Potato Dextrose Agar (Lab M Ltd., Heywood, Bury, UK) slant medium at 5 ◦C for five to seven days in order to observe the growth by microscope
Summary
The red bean (Phaseolus vulgaris) is an herbaceous annual plant of the family leguminosae [1]. Plant foods are fermented to enhance or create unique flavors, to change the textural properties, and to improve quality and digestibility. Rhizopus oligosporus has been used in Indonesia to produce soybean tempeh (tempe kedele) since ancient times, and interest in this food has increased worldwide [4]. It is normally fried, boiled, steamed or roasted. During incubation with R. oligosporus, the soybeans are bound together by the white mycelium, forming a cake, and enzymes released by the fungus render the protein-rich product more digestible to humans [5]. In addition to cereals and process by-products, can be used as substrates for tempeh [6]
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