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.

Abstract. Rizal S, Murhadi, Kustyawati ME, Hasanudin U. 2020. Growth optimization of Saccharomyces cerevisiae and Rhizopus oligosporus during fermentation to produce tempeh with high β-glucan content. Biodiversitas 21: 2667-2673. Saccharomyces cerevisiae grows and produces β-glucan during fermentation in tempeh production. The content of β-glucan in tempeh is influenced by the growth of S. cerevisiae throughout fermentation. The purpose of this study was to determine the effects of different types and concentrations of carbon sources on yeast growth, fungi growth, and β-glucan content in tempeh inoculated using Rhizopus oligosporus and S. cerevisiae. This study used a Factorial Randomized Complete Block Design (RCBD) with two factors and three replications. The first factor was the types of carbon sources, tapioca and wheat flour; the second factor was the concentrations of carbon source, 0.0%, 2.5%, 5.0%, 7.5% and 10.0% (w/w). Tempeh produced was investigated for yeast number, fungi number, β-glucan content, and pH value. The obtained data were tested using Tukey's Honestly Significance Difference (HSD) test. The results showed that the addition of various types and concentrations of carbon source significantly influenced the increase in yeast number, fungi number, β-glucan content, and pH in tempeh. The growth of yeast, fungi, and β-glucan content increased along with the increment of carbon source concentration. The amounts of yeast, fungi, and β-glucans in tempeh added with tapioca were higher compared to tempeh with wheat flour. The addition of 10% tapioca produced the highest amount of yeast with 9.505 Log CFU/g and the highest β-glucan content with 0.707% (w/w).

Application of supercritical carbon dioxide for processing of food products has an impact on microbial inactivation and food quality. This technique is used to preserve tempeh due to no heat involved. The quality of tempeh is highly influenced by mold growth because of its role in forming a compact texture, white color, and functional properties as well as consumer acceptance. This study aims to observe viability of molds and bacteria in tempeh after processed with supercritical CO2 and to determine the best processing conditions which can maintain mold growth and reduce the number of bacteria in tempeh. For that purpose, tempeh was treated using high pressure CO2 at 7.6 MPa (supercritical CO2) and at 6.3 MPa (sub/near supercritical CO2) with incubation period of 5, 10, 15, and 20 min. The best treatment obtained was used to process tempeh for storage study. The results showed that there was a significant interaction between pressure and incubation period for bacterial and mold viability at ρ>0.05. Reduction of bacteria and molds increased with longer incubation period. Molds were undetectable after treatment for 20 min with either supercritical CO2 or sub-supercritical, and bacteria significantly reduced up to 2.40 log CFU/g. On the other hand, sub-supercritical CO2 for 10 min was the best processing method because molds survived 4.3x104 CFU/gram after treatment and were able to grow during storage at 30°C, producing white mycelium as indicated by increasing the L⁎ color value and tempeh acceptability. The inactivation of mold was reversible causing it to grow back during storage under suitable conditions. Tempeh matrix composition can provide protection against the destructive effects of supercritical CO2. Gram-positive bacteria were more resistant than Gram-negative. In conclusion, sub-supercritical CO2 can act as a method of cold pasteurization of tempeh and can be used as an alternative method to preserve tempeh.

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Kapang, R. oligosporus merupakan mikroba utama yang berperan dalam fermentasi tempe. Penambahan khamir selama fermentasi tempe mempengaruhi kandungan aroma tempe dan diduga menghasilkan beta-glukan dalam tempe. Penelitian ini bertujuan untuk mengetahui pengaruh penambahan Saccharomyces cerevisiae terhadap sifat organoleptik dan kandungan betaglukan pada tempe. Perlakuan terdiri dari 2 faktor yaitu konsentrasi S. cerevisiae yang terdiri dari 1% dan 3%, perlakuan kedua adalah cara pemasakan terdiri dari 2 taraf yaitu tempe digoreng dan dikukus. Sebagai kontrol dilakukan pengamatan terhadap tempe mentah. Pengujian organoleptik, sampel tempe diambil 15 g lalu dimasak sesuai perlakuan kemudian diamati secara organoleptik dengan uji skoring menggunakan 25 orang panelis. Data dianalisis dengan sidik ragam untuk mendapat penduga ragam galat dan uji signifikansi untuk mengetahui pengaruh antar perlakuan. Perbedaan antar perlakuan dianalisis menggunakan Duncan Multiple Range Test (DMRT) pada taraf 5% untuk pengamatan terhadap sifat organoleptik tempe. Pengamatan sifat organoleptik dilakukan terhadap aroma langu, aroma khas tempe, rasa asam dan rasa pahit, dan penerimaan keseluruhan tempe. Hasil penelitian menunjukkan tempe yang dibuat dengan penambahan S. cerevisiae 1% dan digoreng memiliki sifat organoleptik terbaik, yakni aroma khas tempe, bau langu lebih rendah, tidak berasa asam, dan tidak pahit. Meskipun berdasarkan skor penerimaan keseluruhan organoleptik, tempe yang diberi penambahan S. cerevisiae 1% dan digoreng lebih disukai panelis dibandingkan perlakuan lainnya, akan tetapi, penambahan S. cerevisiae 3% menghasilkan tempe dengan kandungan beta-glukan lebih tinggi (0,250%) dibanding penambahan S. cerevisiae 1% (0,181%).