Microbiological analysis of Maltese dry sausages : isolation of lactic acid bacteria and assessment of their survival to low pH, as a basic in vitro probiotic attribute

Abstract

Background: Fermented dry sausages are traditional food products, commonly consumed in the Mediterranean region. These products rely on natural fermentation processes driven by indigenous microbiota and have unique attributes influenced by local microbiota, ingredients, and processing methods. Traditional Maltese dry sausages have yet to be comprehensively studied for their microbial composition and probiotic potential. This dissertation aims to explore the microbial population dynamics of Maltese dry sausages and evaluate the acid tolerance of lactic acid bacteria (LAB) strains isolated from these products to assess their probiotic potential. Methodology: Five samples of traditional Maltese dry sausages, with no added starter cultures were collected, from different local butchers. Microbiological analysis was conducted to enumerate various bacterial groups, including Escherichia coli, Enterobacteriaceae, Total mesophilic count, Salmonella, Yeasts, and moulds, lactococci, and LAB. LAB strains were isolated using de Man, Rogosa, and Sharpe agar (MRS). Their resistance to low pH (pH 2.5) was tested to assess their acid tolerance. Resistance was assessed through viable colony counts at 0, 0.5, 1, 2, and 3 hours. Statistical analysis used the test of analysis of variance (ANOVA) to identify significant differences in survival rates (p < 0.05). Results: Microbial analysis revealed variations in microbial populations across different sausage samples, with LAB strains dominating on MRS and M17 media. This indicates the potential responsibility of LAB for fermentation processes. The acid tolerance test on isolates obtained from MRS showed a marked decrease in survival rates over a 3-hour incubation period, with none of the strains having a final population exceeding 103 CFU/mL at the 3-hour time point. This finding suggests potential limitations in the probiotic potential of the specific LAB isolates, since microorganisms classified as probiotics typically demonstrate robust acid tolerance. Conclusion: The study sheds light on the microbial composition of traditional Maltese dry sausages and underscores the importance of further research to elucidate the probiotic potential of LAB strains in these food products. Future research should address limitations such as small sample sizes and resource constraints, while also conducting comprehensive probiotic assessments to better understand the health benefits associated with LAB strains in traditional Maltese cuisine.