Antimicrobial effect and shelf-life extension by combined thermal and pulsed electric field treatment of milk

Aims: The impact of a combined hurdle treatment of heat and pulsed electric fields (PEF) was studied on native microbiota used for the inoculation of low-fat ultra-high temperature (UHT) milk and whole raw milk. Microbiological shelf-life of the latter following hurdle treatment or thermal pasteurization was also investigated. Methods and Results: UHT milk was preheated to 30°C, 40°C or 50°C over a 60-s period, pulsed for 50 μs or 60 μs at a field strength of 40 kV cm^-1 or for 33 μs at 50 kV cm ^-1. Heat and PEF reduced the microbial count by a maximum of 6.4 log in UHT milk (50°C; 50 kV cm^-1, 33 μs) compared to 6.0 log (P ≥ 0.05) obtained by thermal pasteurization (26 s, 72°C). When raw milk was treated with a combination of hurdles (50°C; 40 kV cm^-1, 60 μs) a 6.0 log inactivation of microbiota was achieved and microbiological milk shelf-life was extended to 21 days under refrigeration (4°C) vs 14 days in thermally pasteurized milk. Native microbiota was decreased by 6.7 log following conventional pasteurization. Conclusions: The findings suggest that heat and PEF achieved similar inactivation of native microbiota in milk and longer stabilization of microbiological shelf-life than thermal pasteurization. Significance and Impact of the Study: A hurdle approach of heat and PEF could represent a valid milk processing alternative to conventional pasteurization. Hurdle treatment might also preserve native milk quality better due to less thermal exposure.