Effect of microwave pasteurization on orange juice color and carotenoid pigments

In this paper changes in carotenoid content and orange juice colour during microwave (MW) heating were studied. Trials were performed on 250 ml stirred orange juice heated at different temperatures (60-70-75-85°C), in a MW pilot plant, able to keep prescribed temperature levels of samples by using infrared thermography temperature readout. The pasteurization conditions of orange juice, generally based on inactivation of the heat sensitive fraction of pectin methyl-esterase (PME), in our trials were achieved after about 1 min at 70°C of MW heating (data not reported). Carotenoid content in fresh juice after MW heating at different levels of temperature decreased of about 13% (70,°C 1 min), 44% (75°C, 1 min), and 52 % (85°C, 1 min). Zeaxanthin and D-carotene are responsible for visual colour of the fresh and pasteurized juices. After 1 min of MW heating, Dcarotene decreased of about 28% at 70°C, 44% at 75° C and 65% at 85°C. As expected the orange juices processed at 75°C and 85°C showed higher col our differences than the orange juices heated at 60°C and 70°C.