Effects of Drying Conditions on Hot-air Drying Characteristics and Quality of Goji Berries

This study investigated the quality of goji berries by analyzing the effects of three drying temperatures (40, 50, and 60 ℃), immersion pretreatments in sodium carbonate, sodium sulfite, and citric acid solutions, and staged temperature variations on drying characteristics, polysaccharide, total phenolic, total flavonoid, betaine, carotenoid contents, 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity and color. Results indicated that increasing the drying temperature, applying solution immersion pretreatments, or utilizing staged temperature variations shortened the drying time of goji berries. Specifically, goji berries dried using staged temperature variations exhibited the highest polysaccharide content, while those pretreated by immersion before drying showed higher levels of total flavonoids, betaine, and carotenoids. Additionally, goji berries pretreated with sodium sulfite solution demonstrated the highest DPPH scavenging capacity (76.11%) and the lowest total chromatic aberration (ΔE=5.92). In contrast, those dried using staged temperature variations (40 ℃ for 10 h, followed by 50 ℃ for 10 h, 60 ℃ for 10 h, and finally 40 ℃ until the completion of the drying process) revealed the highest total phenolic content (10.24 mg GAE/g). Cluster analysis indicated differences among the four drying methods, with natural sun drying displaying the greatest disparity compared with the other methods. Correlation analysis revealed correlations among polysaccharide, total phenolic, total flavonoid, and carotenoid contents. Except for betaine, the DPPH scavenging capacity showed an insignificant correlation with the other quality indices. Immersion pretreatment technology can produce high-quality dried goji berries while reducing drying time. These results provide a reference for improving the drying and processing technology of goji berries.