Pasteurization of mandarin juice by ohmic heating and evaluation of its shelf-life under refrigerated and ambient conditions

Mandarin juice was treated inside a bath ohmic heater at 15 different combinations of voltages (120, 160, and 200 V) and treatment times (30, 60, 90, 120, and 150 s) targeting 85 degrees C. The come-up time to reach 85 degrees C for 120, 160, and 200 V were 240, 180, and 100 s, respectively. The system performance ranged between 88% and 98%. Ohmic heating rates increased with the applied voltage reaching 0.545 degrees C s(-1) at 200 V. Ohmic heating at 200 V/30 s and 160 V/90 s produced a microbially safe mandarin juice (5 log reduction in natural microflora); whereas 200 V/30 s, 160 V/90 s, and 120 V/150 s treatments led to an enzymatically stable (>99% spoilage enzyme inactivation) mandarin juice. Under the pasteurized condition of 200 V/30 s, there was only a 10% and 8.4% loss in vitamin C and total phenolics in the juice. Elevated antioxidants were observed after ohmic heating. Lightness and total color change (Delta E*) of the juice increased with ohmic heating. The maximum browning of 66.74 was observed in the juice treated at 120 V/150 s. The juice treated at 200 V/30 s showed a shelf life of 42 and 15 days under refrigerated and ambient conditions, respectively.