Investigation of the native microflora and isolation of protective starter culture for a traditional Vietnamese fermented meat
Creators: name: Tran, Khanh
Publisher: name: RMIT University
Year: 2025

description: <i>Nem chua</i>is a traditional Vietnamese uncooked fermented pork sausage, which has been one of the most important traditional foods consumed in festive celebrations and also as a part of the daily diet. However, despite its popularity, <i>nem chua</i> is still mainly produced by small family businesses using traditional methods and practices that are based on art rather than science. The fermentation process, the key hurdle to ensure the product safety, occurs naturally without the use of starter culture or only with back-slopping, a practice employing a small amount of previous successful batch as the starter for the fermentation of a new batch. The practice of natural fermentation or the repeated use of back-slop in fermented meat production implies significant risks of contamination. This project was thus objected to investigate the hygienic status and native microflora of <i>nem chua</i><br> and develop the protective starter culture for this product.The outcome of the study on the hygienic status of <i>nem chua</i> revealed that 93% of the samples tested were classified as unacceptable. Using the Australian microbiological guidelines for uncooked fermented meat, 92.2% of the samples were classified as unacceptable for <i>Enterobacteriaceae</i>, 53.3% as unacceptable for <i>Escherichia coli</i> and 56.6% as unacceptable for coagulase-positive staphylococci. <i>E. coli</i> O157:H7 was unexpectedly detected in <i>nem chua</i><br> but confirmed to be non-toxigenic. These results indicate hygienic deficiencies in sausage processing and the need to improve poor handling practices.The investigation of the native microflora of <i>nem chua</i> revealed that lactic acid bacteria (LAB) were predominant in <i>nem chua</i> microflora, accounting for 80 − 100% of total viable counts. It was found that 67.6% of all LAB isolates belonged to the species <i>Lactobacillus plantarum</i>, followed by <i>Pediococcus pentosaceus</i> (22.7%) and <i>L. brevis</i> (9.3%) with only one isolate (1.4%) being a <i>L. farciminis</i>. A great genetic plasticity was observed among LAB isolates within the same species, with similarities ranging from 16.9 to 100%. These results suggest the great diversity of <i>nem chua</i><br> sensory characteristics among different regions of Vietnam.For the potential use as protective starter culture, two strains of LAB, namely <i>L. plantarum</i> A17 and <i>L. plantarum</i> B21 with the strongest production of acid and antimicrobial agent were isolated and identified. These two starter cultures were successfully used to control <i>E. coli</i> in the challenge studies with both strains capable of reducing <i>E. coli</i> by more than 4 logs. The strain <i>L. plantarum</i> B21 was also proven to produce an acid and heat stable bacteriocin. In view of its interesting characteristics, this bacteriocin has an application potential as a natural preservative in <i>nem chua</i> as well as other pasteurised, acid or non-acid foods. The successful isolation and identification of two new strains of LAB will have enormous benefit as potential starter cultures for commercial production of <i>nem chua</i><br> with export potential to the Asia Pacific region.