Assessment of the thermal treatment of orange juice during continuous microwave 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 and hydroxymethyl furfural (HMF) contents, as well as degree of browning). Results were compared with those obtained using a conventional tubular heat exchanger having the same heating and cooling phases. The continuous microwave process proved to be an effective system for PME inactivation without the inclusion of a holding phase. In general, no differences were found between the two systems used in the majority of the indicators studied, except that a slight decrease was observed in the most reactive amino acids in the case of conventionally heated orange juice. This fact could be due to overheating of the juice at the tubular heat exchanger.