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. 2021 Jun 16;30(6):861-868.
doi: 10.1007/s10068-021-00915-x. eCollection 2021 Jun.

Dominant Enterobacteriaceae in tempeh were primarily originated from soybean

Horizon M Ilham  1 , Michael Wijaya  2 , Antonius Suwanto  1   3 , Iman Rusmana  1
Affiliations

Dominant Enterobacteriaceae in tempeh were primarily originated from soybean

Horizon M Ilham et al. Food Sci Biotechnol. .

Abstract

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.

Keywords: ERIC-PCR; Enterobacteriaceae; Klebsiella; QRT-PCR; Soybean.

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Conflict of interest statement

Conflict of interestAll authors declare no conflicts of interest.

Figures

Fig. 1
Fig. 1
Bacterial population in pre-boiling soy, post-boiling soy, and fresh tempeh samples from two different tempeh producers (RTI and EMP)
Fig. 2
Fig. 2
Enterobacteriaceae populations in different stages of tempeh (RTI and EMP) production
Fig. 3
Fig. 3
Comparison of viable count and qPCR analysis on Enterobacteriaceae enumeration at several stages of tempeh (RTI and EMP) production
Fig. 4
Fig. 4
Composition of dominant bacteria based on colonies grown on EMB agar. A RTI and B EMP
Fig. 5
Fig. 5
ERIC-PCR profiles of K. pneumoniae isolates; (M) Marker, (PrR) pre-boiling soy RTI, (PsR) post-boiling soy RTI, (FTR) fresh tempeh RTI, (PrE) pre-boiling soy EMP, (PsE) post-boiling soy EMP, (FTE) fresh tempeh EMP, (EI) K. pneumoniae EMP isolate from previous study (Ayu et al., 2014), and (MI) K. pneumoniae isolate originated from hospital (Ayu et al., 2014)
Fig. 6
Fig. 6
Phylogenetic tree of K. pneumoniae isolates constructed from the results of ERIC-PCR. (PrR) pre-boiling soy RTI, (PsR) post-boiling soy RTI, (FTR) fresh tempeh RTI, (PrE) pre-boiling soy EMP, (PsE) post-boiling soy EMP, (FTE) fresh tempeh EMP, (EI) K. pneumoniae EMP isolate from previous study (Ayu et al., 2014), (MI) K. pneumoniae isolates originated from hospital (Ayu et al., 2014)
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