Effect of Thermal Treatment on Lactic Acid Bacteriophages

If starter culture bacteria are infected with bacteriophages, it results in poor or faulty fermentation of cheese and fermented milk. Despite strict sanitation measures, culture rotation, and special equipment design, bacteriophages with their growing heat resistance remain a serious biotechnological problem for the dairy industry. As a rule, raw milk is the main source of highly mutating bacteriophages with various heat resistance values. Bacteriophages are more resistant to heating than the host strain and most vegetative microbiota; however, scientific publications provide contradicting data on the effect of thermal exposure on lactic acid bacteriophages in various environments. As a result, industrial bacteriophage inactivation requires additional studies to define the most efficient modes. The article introduces the optimal modes of physical bacteriophage inactivation and pasteurization as part of phage monitoring. The authors analyzed available reports on types and groups of lactic acid phages typical of dairy plants, the nature of their heat resistance, and their adaptive evolution to increasing sublethal temperature. The standard methods of analysis and synthesis made it possible to reveal the effect of thermal action on lactic acid bacteriophages in different laboratory conditions. The resulting optimal thermal modes of fermented dairy production may help to develop a system of effective practical antiphage measures that could be compiled into a Program of Preliminary Measures of Phage Monitoring. Although the recommendation for a stricter heat treatment of raw milk does not find unanimous support, dairy plants may apply thermal antiphage inactivation if the processing involves boiling or steaming.