Milk pasteurization by induction heating and its effect on the microbiological quality of milk

Increasing the pasteurizing temperature of contaminated milk in classic method for completing the heating process causes burning the milk layer on pasteurizer and creates thick milk stone. This event in addition to prevents the sufficient transfer of heat, produces carcinogenic compounds, changes in milk color and increases remained microbial load in the milk, therefore threaten the product's health. In the method used in this study (induction heating), electromagnetic current was induced into milk and caused be heated faster than classic method. In this research, milk was pasteurized by using an induction heater in 243 different conditions and optimized method was selected for adequate process via a factorial experiment design. In this experiment, the effects of four different factors including: 1) 3 intensities of electricity transmittance (350, 1000 and 1600 watts), 3 levels of test containers surface (12, 17 and 23 cm), 3 temperatures (72, 75 and 84 °C) and 3 pasteurization time (15, 20 and 30 seconds) were used in three replications. The optimized method was selected respectively in three steps based on 1) the minimum percentage of microbial load, 2) a minimum elapsed time for milk pasteurization and 3) the lowest energy consumption for processing. Consequently, the results showed that the destruction of total bacterial load was 99.5 % in selected induced heating method in comparison to classic method (98.23%). Moreover, Coliform and Escherechia counts in induced heating method have been one tenth to classic method. In induced heating method, milk stone wasn’t produced due to the fast heating transfer.