Impact of starter culture on quality and proteolysis of soybean tempeh

This study investigated the microbiological composition of a commercial tempeh starter and analyzed its effect on the microbiological, amino acidic and peptidolytic profile of soybean-based tempeh. The results highlighted that the high quality of the commercial starter culture is critical for safe tempeh fermentation. The starter contained a dominant population of Eumycetes (6.3 log CFU/g) along with minor contaminants such as lactic acid bacteria (4 log CFU/g) and Bacillus spp. (5.3 log CFU/g). High-throughtput sequencing confirmed that the genus Rhizopus accounted for approximately 86 % of the fungal community of tempeh starter, while other fungal families such as Pleosporaceae and Trichosphaeriaceae , represented less than 5 % each. Results showed that the primary fermentation agent, Rhizopus spp., produces proteolytic enzymes that break down soy proteins into smaller peptides and free amino acids. The study identified 19 bioactive peptides, derived mainly from the proteins conclycinin, glycinin and oleosin, with potential antioxidant, anti-hypertensive and antimicrobial properties. Overall, the use of a selected microbial starter proved crucial in enhancing the quality and digestibility of soybean tempeh through the generation of bioactive peptides with potential health benefits.