Dominant Enterobacteriaceae in tempeh were primarily originated from soybean.

During tempeh production, boiling was considered as heat treatment that could significantly reduce or eliminate bacterial population in soybean before fungal inoculation. The objective of this study was to enumerate and trace Enterobacteriaceae communities in pre-boiling soybean, post-boiling soybean, and fresh tempeh designated as RTI and EMP. Standard plate count and qRT-PCR were employed to determine the culturable and non-culturable bacteria, while Enterobacterial Repetitive Intragenic Consensus PCR was conducted to determine the intraspecies genomic variations. Fresh tempeh from both RTI and EMP contained approximately 107 and 108 CFU/g of Enterobacteriaceae respectively. The number of bacteria in pre-boiling soybean were 10,000 times lower than in fresh tempeh. Our study showed that most Enterobacteriaceae were severely injured or quiescent during boiling process and quickly recovered up to 109 CFU/g in fresh tempeh. Some Klebsiella isolates found in tempeh were genetically identical to isolates in soybean, but different from those of medical isolates. This study suggested that soybean could be the main origin of Klebsiella in fresh tempeh. © The Korean Society of Food Science and Technology 2021.