Microbiological safety of traditionally processed fermented foods based on raw milk, the case of Mabisi from Zambia

For centuries, perishable raw materials such as raw milk have been processed through traditional fermentation. For many, microbiological safety has not been assessed systematically. Here, we study the microbiological safety of an archetypical traditional fermented raw milk product with high cultural importance: Mabisi from Zambia. We focus on traditional processing without the use of defined starter culture – a method that is employed by local small-scale processors at home or at farmer cooperatives. In a field survey, we found that food associated pathogenic bacteria such as Salmonella sp. and Staphylococcus aureus were present in raw milk used for processing. In processed Mabisi these pathogens were found to be present albeit at levels that fall below common limits of microbiological safety for dairy products. In standardized laboratory experiments, we investigated the microbiological safety of traditionally processed Mabisi using challenge tests with important pathogens related to raw milk and Mabisi. Strains of S. aureus, Salmonella and Listeria monocytogenes could survive fermentation and were present in the end-product after 48 or 72 h of fermentation, yet below legally set thresholds of acceptability. Our work shows that use of traditional processing methods for fermentation of raw milk can result in products that are microbiologically safe.