Effects of different drying methods on quality and water distribution of Lycium barbarum

Abstract

AbstractAlthough Lycium barbarum is a valuable medicinal food, it is unfortunately not easy to store due to its high moisture content. In order to maximize the preservation of the medicinal value of L. barbarum, drying is increasingly used for its storage. Motivated by the need to better understand and improve the drying of L. barbarum, in this study, the VFD (vacuum freeze drying) and HD (hot air drying) are employed as drying processes, and the rehydration ratio, drying time, specific energy consumption, sensory characteristics, moisture ratio, energy consumption, moisture mobility, and amino acids and flavonoids content of dried L. barbarum are comprehensively analyzed. The results show that, after VFD, L. barbarum has lower hardness (71.53 ± 1.68), higher rehydration ratio (1.31 ± 0.02), larger volume, plump, round and smooth surface, and similar color to the fresh L. barbarum. At the same time, compared with the sample after HD, the moisture ratio of L. barbarum after VFD is lower (1.4 ± 0.1), and its content of free water is almost negligible (2.2%). In addition, the amino acids and flavonoids content of L. barbarum after VFD are closer to those of the fresh product (133.7 μmol/g, 5.69 mg/g). Based on the analysis of the drying effect on the physical and chemical properties of L. barbarum, we conclude that VFD is a promising processing technology. However, HD proves to greatly reduce the specific energy consumption and drying time when raising the temperature appropriately, whereas VFD could not achieve the same result by increasing the heating rate of VFD.Practical applicationsIn this paper, based on the mechanism of different drying methods, the quality of L. barbarum products after drying was compared, and the water distribution in the drying process was analyzed. It is found that using VFD technology to dry L. barbarum can improve the production efficiency of L. barbarum industry and the quality of L. barbarum products. Meanwhile, the research results can provide reference for the optimization of VFD system and the scientific formulation of process parameters.