Storage quality of fresh Lycium barbarum by vacuum precooling and microporous membrane packaging

Abstract: Fresh Lycium barbarum (wolfberry) is one of the most popular medicinal and food supplements in China. The favorite taste and rich nutrients substances have drawn much more attention, with emphasis on a wide range of health benefits in recent years. Nevertheless, the postharvest fresh Lycium barbarum generally presents high respiratory climacteric intensity and very active physiological responses. Specifically, the fruit stalk is easy to fall off during ripening, which makes the juice of Lycium barbarum flow out and prone to mold pollution. As such, the preservation period of postharvest fresh fruit is only 2-3 days under normal temperature, indicating a very high occurrence of damage rate. Therefore, a great challenge still remains on the preservation of fresh Lycium barbarum fruit. Fortunately, vacuum precooling can quickly eliminate the field heat of fresh Lycium barbarum, while reducing the respiratory intensity. Since the precooling is very remarkable, only a few efforts were made on the vacuum precooling in the fresh Lycium barbarum. Furthermore, the respiration rate is relatively high in the fresh Lycium barbarum after harvest, which the air permeability of ordinary film cannot meet. It is easy to cause low oxygen concentration and high carbon dioxide concentration in the membrane, resulting in anaerobic respiration and carbon dioxide poisoning of fresh Lycium barbarum, and ultimately losing the nutritional value of fresh Lycium barbarum. Therefore, a high permeability film is highly demanding to deal with the breathing problem of fresh Lycium barbarum. Particularly, microporous film preservation is widely expected to be an ideal preservation way at present. In this study, the storage quality of fresh Lycium barbarum was investigated using vacuum precooling combined with microporous membrane packaging. The weight loss rate, wax layer, and respiration rate of fresh Lycium barbarum were also compared to determine the optimal process parameters. The fresh Lycium barbarum with vacuum precooling under the best process parameters was packaged with the microporous membrane, and then kept in cold storage at (-1 ± 0.5) ℃. The fresh Lycium barbarum with microporous membrane packaging and without any treatment was taken as the control group, and then kept in cold storage under the same storage conditions. The hardness, Total Soluble Solids (TSS), color, respiratory intensity, and Catalase (CAT) activity of fresh Lycium barbarum during storage were measured to comprehensively analyze the effects of different treatments on the storage quality of fresh fruit. The results showed that the final temperature of 6℃ and final pressure of 800-1 000 Pa posed little effect on the weight loss rate of fresh Lycium barbarum; the final temperature 6 ℃ and final pressure 1 200-1 500 Pa had little damage to the inner epidermis structure of fresh fruit; the final temperature 2 ℃ and final pressure 800-1 000 Pa presented the lowest respiratory intensity of fresh fruit. Consequently, the final temperature of 6 ℃ and the final pressure of 1 200-1 500 Pa were the optimal process parameters for the vacuum precooling of fresh Lycium barbarum. At the same time, the vacuum precooling combined with microporous membrane packaging during storage can effectively delay the decline of hardness and TSS, while reducing the respiratory intensity, color change, and CAT activity, compared with the control group. This finding can provide important theoretical support for the production of fresh Lycium barbarum using vacuum precooling technology.