PCR-RFLP typification of microbes used in the production of a fermented fish product

[摘要] ENGLISH ABSTRACT:The preservation of various fresh fish products is achieved by either smoking,salting, canning, freezing or fermenting a highly perishable raw product. Sincemany of these facilities are not readily available, the use of fermentation as ameans of preserving the product has been extensively practiced. However, thefermentation of fish is a time consuming practise and only by accelerating theprocess would it be possible to ensure the production of a more cost effective andreadily available safe end-product.The quality of the fermented fish product is partially determined by thefermentation conditions and the metabolic activity of the microbes present. Therapid identification of the microbes present during the fermentation would enablethe selection of possible starters to ensure an accelerated production of highquality fermented fish products. This study was thus undertaken to developidentification fingerprints for bacteria isolated from fermented fish products. A1300 bp fragment of the 16S rRNA genes of each of the bacteria previouslyisolated was successfully amplified using the PCR technique. The isolatesincluded strains of the genera Bacillus, Staphylococcus, Sphingomonas, Kocuria,Brevibacillus, Cryseomonas, Vibrio, Stenotrophomonas and Agrobacterium. Thedata obtained can, therefore, be used in the identification of these microbesisolated from other similar fermented fish products. The fingerprints could also beused to assist in determining the dominant microbial populations responsible forthe characteristic qualitative changes occurring in the fish product duringfermentation.The microbial composition of a fermenting fish product partially determinesthe quality of the end-product, therefore, the use of selected bacterial starterscould result in the accelerated production of a microbial safe fermented fishproduct. A further objective of this study was to accelerate the production of afermented fish product by inoculating macerated trout with either selected lacticacid bacteria (LAB) or with selected bacteria with high proteolytic activity over a 30day fermentation period. The LAB included a combination of Lactobacillusplantarum, Lactococcus diacetylactis and Pediococcus cerevisiae strains, whereasthe bacteria with high proteolytic activity included strains of Kocuria varians,Bacillus subtilis, two strains of B. amyloliquefaciens and a combination of these bacterial species. The quality of the fermented product was determined usingchanges in product pH, titratable acidity (%TA) and free amino nitrogen (FAN)formation as efficiency parameters.The data obtained during the fermentation of the macerated trout showedthat the selected starters did not have a significant effect on the pH decrease inthe product over a 30 day fermentation period. The LAB strains did not have asignificant effect on the %TA of the fermenting fish product, yet the presence ofthese bacteria appeared to limit the FAN production in the product. The bacteriawith high proteolytic activity resulted in slightly enhanced %TA values and a higherFAN content in the fermented product. It was also determined that the LAB andKocuria varians, in contrast to the Bacillus spp. inoculums, did not survive thefermentation conditions well, possibly due to the low pH environment. Thepresence of the starter bacteria in the fermenting fish mixture at the end of thefermentation was also successfully determined with the use of the PCR-RFLPtechnique.The fermented fish product, obtained at the end of the fermentation period,had a good aroma and compared favourably to similar commercially availablefermented fish products. The use of different microbial starters could in futureenable the production of a diverse range of high quality products, which could beproduced and marketed locally.

[发布机构] Stellenbosch University