ABSTRACT
4 5The best voltage for milk pasteurization by using ohmic heating was 80 V compared with 110, 220 V, both of which were inadequate for pasteurization. Heating at 80 V was safer and inexpensive as it required less power (80 V) in contrast with higher voltages (110-220 V) and less dangerous. Voltage of 80 V does not change milk color to brownish as it was noticed at 110- 220 V and undesirable smells were not present. Heating at 80 V did not cause fouling or precipitation of deposits on electrodes compared to 110-220 V. The best electrical conductivity was at 80 V as there were no deposits on the electrodes. The practical temperature of milk was stable because of the thermal valve, which controls the temperature at 72°C. The electric conductivity and current were increased with increasing temperature in ohmic heating at 220, 110, and 80 V while these were decreased with the increase of temperature at 220 V. The thermal conductivity and thermal diffusivity were increased with the increase of temperature at all voltages in the ohmic heating and high time short temperature (HTST).The introductory part of this chapter includes importance of thermal processing of milk, existing heating methods used and their effects on different quality characteristics. Authors explored alternative methods for thermal processing of milk and milk products, and briefly discussed microwave-assisted processing with recent research findings. Further, they discussed the influence of microwave heating on physicochemical properties, microbial destruction, enzyme inactivation, and volatile components of milk. Finally, they concluded that microwave heating has potential to meet industrial needs as an alternative technology for thermal processing of milk.
The viscosity of milk and its density were decreased with the increase of temperature at all voltages in the ohmic heating and HTST. The period of keeping milk in the device was decreased with the increase of voltage in the ohmic heating, which was less than HTST. At 80 V of treatment, the highest coefficient of performance was 0.80, compared with 220, 110 V, with performance coefficient of 0.49 and 0.76, respectively. The percentages of protein, lipid, lactose, ash, and humidity in raw milk were 3.6, 3.7, 5.02, 0.68, and 87.0%, respectively. These values at 80 V were 3.5, 3.6, 6.2, 0.69, and 85.9%, respectively; and at 110 V were 3.54, 3.6, 6.9, 0.69, and 85.2%, respectively; and at 220 V were 3.5, 3.6, 7.1, 0.73, and 85.0%, respectively, and in HTST were 3.57, 3.7, 6.0, 0.71, and 87.0%, respectively.
The percentage of acidity in raw milk was 0.15% and was 0.14, 0.14, 0.13, and 0.15%, respectively, for ohmic heating at 220, 110, 80 V, and HTST. The pH prior the pasteurization was 6.6 compared to 6.7, 6.8, 6.8, and 6.8 after the pasteurization by ohmic heating at 220, 110, 80 V, and HTST treatment, respectively. The phosphatase enzyme test gave positive results in raw milk and negative one in pasteurized milk treated either by ohmic heating on all voltages and HTST. The clot on boiling test and turbidity test gave negative results for raw milk. The microbiological results of pasteurized milk by ohmic heating showed no colonies in total 6count bacteria, coli form, Staph-110, yeasts, and molds. Milk treated by HTST pasteurization had bacteria while bacteria were absent. The shelf- life study of pasteurized milk by ohmic heating at 4°C for 15 days showed no change in pH and acidity. The results also showed no colonies in bacterial total count bacteria, coli form, staph-110, yeasts, and molds. However, pasteurized milk by both methods (ohmic and HTST) could only be stored for 72 h at room temperature. The HTST treated milk could be stored for 8 days at 4°C for 8 days.
