Effect of Using Microwave Radiation in Milk Pasteurization

Abstract

The aim of the present study is to modify a microwave device to be used as a continuous pasteurization device and to study the ability of the device to inhibit microorganisms٫ and to improve the thermo-physical and chemical properties of the pasteurized milk. The buffalo milk was pasteurized by microwave at 72° C for a time ranging between 20 -400 seconds, then a sudden cooling was introduced in the refrigerator at a temperature of 5° C and stored on this degree for a period of 15 days. The microbial and chemical analysis were performed, Each milk sample was divided into four groups: A, B, C and D, where group (A) represents the milk control sample, group (B) represents the milk subjected to radiation intensity of 800W with flow rates of 75, 150 and 225 ml/20 – 40 – 80 seconds respectively, group (C) represents the milk subjected to radiation intensity of 480W with flow rates of 75, 150 and 225 ml/ 40 – 80- 160 seconds respectively and group (D) represents the milk subjected to radiation intensity of 160 W with flow rates of 75, 150 and 225 ml / 100 – 200 – 400 seconds respectively, keeping the coil length of 200 cm constant for all the previous treatments. The device productivity reached 13.5 liters/hour and heating rate was 3.6°C/second. Results showed that chemical properties of milk were as follows: pH, fat, protein, lactose, ash values of group (B) was significantly higher than control sample (P <0.05), followed by group (C) and group (D), while the titratable acidity, moisture values was significantly less than the control sample (P <0.05). Microbiological tests before treatment included the total number of microbes, coliform group. After microwave treatment, the thermo-physical properties of milk included density, thermal conductivity, viscosity, and specific heat at different temperatures were also calculated. The results were: (1031.146 - 1012.792 kg/m3) ،(0.566191 - 0.644071w/m.k)، (0.000858 - 0.0006901 Pa.s)،(3855 - 3939 J/kg.k) respectively. The results were seriously significantly increased by increasing the heating time compared to the control samples (p < 0.05)٫ whereas the viscosity of milk and its intensity were significantly decreased by increasing the heating time in comparison to the control sample (p < 0.05). Results had been improved that after pasteurization where the total number of microbes, chloroform group, tuberculosis, Lysteria microbes and alkaline phosphatase had been eliminated in the pasteurized milk.