2^nd International Dairy Meet & Expo

Dairy Bacteriophages and Fermentation

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Knowledge of phage-host interactions at a fundamental level is central to the design of rational strategies for the development of phage-resistant strains that may be applied in industrial settings. The potential of currently investigated dairy phages in turn serve as model systems for a particular group of phages. In a fermentative dairy process, lactic acid bacteria (LAB) growth and metabolic activities are needed to assure a high-quality final product. The growth of dairy starter cultures can be influenced by a number of factors including the raw milk quality, presence of antibiotics or sanitizers, bacterial interactions, and phages. Although raw milk is the most logical source of phages in the industrial environment, several dispersion pathways may be occur in dairies. Aerosolization is currently recognized as an important route of dispersion. Additional underestimated sources of phage contamination are the working surfaces in the dairy facilities. The dairy industry, particularly cheese manufacturing, recycles whey protein concentrates (WPC) to increase product yield and/or enhance attributes of the final product. However, such a process is risky due to the possible presence of phages in these ingredients. To compound the risk associated with WPC, whey is frequently concentrated (ultrafiltration or microparticulation), thereby increasing the phage levels due to the possible retention of virions by the membranes. A general recommendation to minimize problems associated with WPC should consider its addition only to a fermentation involving the use of significantly different starter cultures, such as mesophilic and thermophilic bacteria. Early phage detection in raw milk, ingredients or the dairy environment is designed to diminish and control phage attacks during the fermentation processes. Two general types of phage detection methods are available: direct and indirect. Direct detection methods focus on detecting the presence of lytic phage particles or their components (DNA, proteins) in a sample. Standard microbiological methods, i.e., plaque assays, spot tests and activity tests, are usually applied to milk or fermented products (cheese whey and fermented milks). One of the advantages of this type of technique is discrimination between phage and non-phage inhibitors. Disadvantages include the requirement for a sensitive indicator strain and the relatively long time needed to obtain results. Of the traditional indirect methods, the activity test is one of the most commonly implemented for routine analysis in dairy plants. Another indirect method proposed for monitoring the fermentation process involves flow cytometric analysis.