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Extreme thermal stability of Lactococcus lactis bacteriophages: Evaluation of phage inactivation in a pilot-plant pasteurizer

Wagner, Natalia, Matzen, Sönke, Walte, Hans-Georg, Neve, Horst, Franz, Charles M.A.P., Heller, Knut J., Hammer, Philipp
Lebensmittel-Wissenschaft + [i.e. und] Technologie 2018 v.92 pp. 412-415
Lactococcus lactis, bacteriophages, heat inactivation, heat stability, raw milk, stainless steel, temperature
Thermal inactivation of highly heat-stable Lactococcus lactis phages P680 and P1532 of the 936 group and P635 of the c2 group was investigated in a pilot-plant pasteurizer after suspension of the phages in raw milk (107 pfu/ml). The heat-sensitive reference phage P008 was tested as a control. The titers of the phages P008 and P635 decreased ≥99.99% after heating for 32 s at 75 °C and 80 °C, respectively. To achieve a similar inactivation of ≥99.99%, phages P680 and P1532 had to be treated for 39 s at temperatures of 95 °C and 97.5 °C, respectively. D- and z-values for thermal inactivation were calculated for each of the phages. When comparing thermal inactivation data of phages in the pilot-plant pasteurizer obtained in this study with literature data on phage heat inactivation in stainless-steel test tubes in a water bath, the pilot-plant pasteurizer was notably more efficient.