Abstract
Abstract In the present research, tomato juice was concentrated via Ohmic heating with two modes of operation, namely atmospheric condition (OHAC) and vacuum condition (OHVC), and conventional vacuum heating (CVH) as the control mode. The effect of heating conditions on the quality of tomato concentration (lycopene, turbidity, pH and acidity) and electrical conductivity were evaluated. The OHVC reduced the concentration time in the range of 10–30%, compared with the OHAC. The comparison of the mean value of the heating rate indicated that the vacuum application reduced the heating rate by 0.8%. The electrical conductivity of OHAC changed from 0.68 S/m at initiate point to 1.25 S/m at the boiling point then decreased to 1.05 S/m at the end of the process, the corresponding values for OHVC was 0.7, 1.13 and 1.11 S/m. The mean percentage change of pH, acidity, lycopene, and turbidity for OHVC were 0.47, 24.03, 7.99, and −30.77 respectively which were lower to the corresponding value for OHAC and CVH. It appears that the application of vacuum condition in the ohmic heating treatment of tomato juice can preserve juice quality. Industrial relevance Due to the high energy consumption of heating in the conventional processing methods, energy efficient systems are demanded for thermal concentration of juices. Ohmic heating is an emerging technology and a very promising in food industries. Comparing with conventional heating processes, ohmic heating can save energy and provide a rapid and uniform heating of pumpable food, resulting a product with a higher quality. The results showed that vacuum coupled with ohmic heating had a significant effect on quality. One of the keys to reducing the thermal damage to products during manufacture is the shortening of the heating time and reducing the boiling point, ohmic-vacuum heating required a lower time and boil at lower temperature, thereby is more advisable for thermal processing from the point of view of energy saving and quality aspects.
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