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

Abstract

Background: Maltese traditional fermented foods such as the cheeselets have not been extensively evaluated in terms of their microbial composition and probiotic attributes. This study aimed to provide a preliminary insight into the microbial characteristics of the cheeselets whilst investigating the resistance of selected lactic acid bacteria (LAB) isolated from these products, to low pH conditions, which is a key probiotic trait. Method: Cheeselet samples were collected, homogenised, and plated on various media, including those specific for LAB isolation. The pH measurements of the cheeselets were also recorded. The resistance of the LAB isolates to low pH (pH 2.5 at 37°C) was assessed, and the data was analysed. Results: Regarding the microbial analysis, varying levels of bacterial populations were observed, with the main populations being LAB, likely belonging to the genera of Lactobacillus and Lactococci. Salmonella spp. was not detected whilst E. coli was present in one sample. Upon exposure to low pH, a decrease in population was observed in all 18 isolates, which was determined to be statistically significant via a repeated measures ANOVA test with an observed p-value of <0.001 and an F-statistic of 2.534. Five isolates were attributed with moderate tolerance to low pH with a population count exceeding 3 log CFU/mL following three hours of exposure, whilst one isolate (GB8), was considered to have good tolerance as it remained above 6 log CFU/mL throughout exposure. GB8 had the highest survival rate (67%) and the lowest log reduction (3.08 Log CFU/mL) amongst all isolates. Conclusion: This study provides a preliminary insight into the microbial characteristics of artisanal produced traditional Maltese cheeselets. Furthermore, the tolerance of LAB isolates to low pH conditions was successfully examined with several isolates exhibiting moderate to good tolerance. Further research is necessary to expand upon these conclusions and obtain a more comprehensive understanding of the probiotic attributes inherent to Maltese cheeselets.