Newer processing technologies like infrared, microwave processing are being harnessed to optimize the processes to ensure minimum loss of the vital nutrients in processed foods. Vitamin C is an important nutrient known for its potential antioxidant, anticancerous and other health promoting properties. Orange juice is a very popular and rich source of vitamin C. The present research focuses on the status of the vitamin C during thermal treatment of orange juice heated by different methods. The study includes a comparative study of kinetics of vitamin degradation and changes in visual colour as an index of carotenoids. The degradation kinetics of vitamin C and colour in terms of reaction rate constant, destruction kinetics, enthalpy and entropy for different methods of heating are discussed. The destruction of vitamin C was influenced by the method of heating and the temperature of processing. The degradation was highest during microwave heating due to uncontrolled temperature generated during processing. Out of the four methods studied, ohmic heating gave the best result facilitating better vitamin retention at all temperatures. The visual colour is generally used an index of the carotenoid content. The activation energies for both vitamin and colour were within the range of literature reported values of 7.54-125.6kJ/mol. The activation enthalpies agreed with the literature values of vitamin destruction of other food products. The z values also were within the literature values of 20-30 degrees C for vitamin destruction, except for microwave heating. (c) 2004 Elsevier Ltd. All rights reserved.