Changes in the Quality of Dimocarpus longan During the Hot-Air Drying and Microwave Drying Processes

Abstract:

The changes in quality of longan during the hot-air and microwave drying processes were investigated in this study. As a result，the change in browning degree of the longan pulp was closely related to the polyphenoloxidase（PPO） activity. The activation of peroxidase（POD） activity had a connection with the water content of longan pulp. PPO was more sensitive to high temperature than POD. The browning of ascorbic acid was not the major reason for the browning of longan pulp. Microwave drying was well-distributed when two-layer of fresh longan was placed in the microwave chamber. The longan dried by microwave was acceptable in texture. By comparison，the efficiency of microwave drying was significantly higher than that of hot-air drying and the browning degree and PPO activity of the longan dried by microwave drying were both lower than those of the longan dried by hot-air drying. Therefore，microwave drying is more suitable for the drying process of longan than hot-air drying from the viewpoint of quality and time-saving process.