Effects of different concentration methods on physicochemical properties, structure, antioxidant activity and volatile organic compounds of apple juice

• VTA-molecular distillation concentration can better reduce the loss of heat sensitive nutrients in concentrated apple juice (CAJ) • The particle uniformity and solution stability of CAJ were improved by VTA-molecular distillation concentration • VTA-molecular distillation concentration can significantly improve the antioxidant activity of CAJ • VTA-molecular distillation concentration can retain more volatile organic compounds Apple juice (AJ), as a kind of nutritional and functional beverage, often needs to be concentrated in processing, but the traditional concentration method is easy to damage its quality. This study systematically evaluated the effects of thermal concentration, membrane concentration and VTA-molecular distillation concentration on the quality of AJ for the first time. The results showed that VTA-molecular distillation was superior to other concentration methods in maintaining physical and chemical indexes, nutrient content, microstructure, antioxidant activity and volatile organic compounds (VOCs). Physical and chemical analysis showed that the color of VTA-molecular distillation AJ (VCAJ) was the closest to AJ, and its clarity was the highest (90.8%), and its browning index was the lowest (0.77). Nutritional analysis showed that compared with other concentrated forms, VCAJ retained higher levels of vitamin C (86.3%) and soluble protein (86.4%), indicating that it had better preservation effect on heat sensitive nutrients. In addition, the particle size (46 µm) and Pdi level (0.41) of VCAJ were smaller, and the uniformity was improved. Correlation analysis showed that the high content of nutrients and uniform microstructure in VCAJ were closely related to the maintenance of antioxidant activity. In addition, GC-IMS analysis showed that 36 of the 47 volatile organic compounds in AJ were retained in VCAJ, which was helpful to maintain the flavor characteristics of fruit aroma, nut aroma and fresh aroma. This study fully confirmed that VTA-molecular distillation is a green and efficient concentration method that can maintain the sensory, nutritional quality and functionality of AJ.