Thermal inactivation of poliovirus type 1 in water, milk and yoghurt

Loss of infectivity of poliovirus type 1, strain Sabin, during heating, freezing, and storage in water, milk and yoghurt was determined by plaque-titration in Vero cell cultures. The heating experiments simulated the conditions arising during the processing of milk and yoghurt, for example high-temperature heating (95 °C, 15 and 30 s), short-time pasteurization (72 °C, 15 and 30 s), long-time pasteurization (62 °C, 30 min), and yoghurt-fermentation (42 °C, 30 min and 180 min). Only high-temperature heating, long-time pasteurization and short-time pasteurization for 30 s proved to be reliable methods of inactivating polioviruses present in water, milk and yoghurt completely. Short-time pasteurization for 15 s and the conditions of yoghurt-fermentation failed to cause complete inactivation of polioviruses. Additionally, polioviruses mixed in milk or yoghurt withstood these procedures with significantly lower reductions of infectivity than in water. Heating at 55 °C for 30 min resulted in complete inactivation of polioviruses, regardless of the suspending medium. The infectivity of polioviruses is scarcely affected by freezing (−20 °C, 30 min) and storage (24 days) at low temperatures (4 °C) and high humidity (aW=0.99).