Inactivation of bacterial pathogens in yoba mutandabota, a dairy product fermented with the probiotic Lactobacillus rhamnosus yoba.

Mutandabota is a dairy product consumed as a major source of proteins and micronutrients in Southern Africa. In this study the microbial safety of traditional and a variant of mutandabota fermented with the probiotic Lactobacillus rhamnosus yoba (yoba mutandabota ) was investigated by challenging the products with five important food pathogens: Listeria monocytogenes , Salmonella spp., Campylobacter jejuni , Escherichia coli O157:H7 and Bacillus cereus . Pasteurized full-fat cow's milk was used for producing traditional and yoba mutandabota , and was inoculated with a cocktail of strains of the pathogens at an inoculum level of 5.5 log cfu/mL. Survival of the pathogens was monitored over a potential consumption time of 24 h for traditional mutandabota , and over 24 h of fermentation followed by 24 h of potential consumption time for yoba mutandabota . In traditional mutandabota (pH 3.4 ± 0.1) no viable cells of B. cereus and C. jejuni were detected 3 h after inoculation, while L. monocytogenes , E. coli O157:H7 and Salmonella spp. significantly declined (P < 0.05), but could still be detected (< 3.5 log inactivation) at the end of the potential consumption time. This indicated that consumption of traditional mutandabota exposes consumers to the risk of food-borne microbial infections. In yoba mutandabota , L. rhamnosus yoba grew from 5.5 ± 0.1 log cfu/mL to 9.1 ± 0.4 log cfu/mL in the presence of pathogens. The pH of yoba mutandabota dropped from 4.2 ± 0.1 to 3.3 ± 0.1 after 24 h of fermentation, mainly due to organic acids produced during fermentation. Only Salmonella spp. was able to grow in yoba mutandabota during the first 9 h of fermentation, but then decreased in viable plate count. None of the tested pathogens were detected (> 3.5 log inactivation) after 3 h into potential consumption time of yoba mutandabota . Inactivation of pathogens in mutandabota is of public health significance because food-borne pathogens endanger public health upon consumption of contaminated food, especially in Southern Africa where there are many vulnerable consumers of mutandabota such as children, elderly and immuno-compromised people with HIV/AIDS. The findings of this study demonstrate that mutandabota fermented with L. rhamnosus yoba has antimicrobial properties against the tested pathogens and it is safer compared to the traditional mutandabota . [ABSTRACT FROM AUTHOR]