The effect of carbonic maceration pretreatment on the vacuum microwave drying characteristics and quality attributes of longan ( Dimocarpus longan Lour)

Traditional drying methods for longan not only take long time, but also cause severe damage to the quality. Carbonic maceration (CM) is an efficient pretreatment that can enhance drying rate and preserve physicochemical properties. The results showed that after CM treatment of 1–5 MPa, the drying time of longan was decreased by 72.62-79.76%. The contents of total, free and bound phenols of longan were increased by 19.18%-52.48%, 33.68%-87.37% and 14.29%-442.86%, respectively. The acidic environment and inactivation of PPO and POD enzymes caused by CM were beneficial in maintaining the stability of phenolic compounds. Furthermore, CM treatment could also increase the active components as it decreased the extraction barrier. So the antioxidant activity was also improved. Moreover, the volatile compounds in dried samples following CM treatments were effectively preserved and exhibited a greater similarity to those found in fresh samples. Therefore, CM is a prospective pretreatment for the dehydration of longan.