ASSESSMENT OF THE THERMAL-TREATMENT OF ORANGE JUICE DURING CONTINUOUSMICROWAVE AND CONVENTIONAL HEATING

The effect of continuous-flow microwave heat treatment of orange juice was evaluated by using parameters of quality (pectin methylesterase ( PME) inactivation and ascorbic acid, free amino acids, carbohydrates a nd hydroxymethyl furfural (HMF) contents, as well as degree of brownin g). Results were compared with those obtained using a conventional tub ular heat exchanger having the same heating and cooling phases. The co ntinuous microwave process proved to be an effective system for PME in activation without the inclusion of a holding phase. In general, no di fferences were found between the two systems used in the majority of t he indicators studied, except that a slight decrease was observed in t he most reactive amino acids in the case of conventionally heated oran ge juice. This fact could be due to overheating of the juice at the tu bular heat exchanger. (C) 1998 Society of Chemical Industry.