Lycium barbarum L. belongs to Solanaceae, Solaneae, Lyciinae, Lycium L. The traditional Chinese medicine Lycii Fructus refers to the mature and dry fruit of Lycium barbarum L.. Modern pharmacological studies have demonstrated that Lycium barbarum L. presents multiple biological activities, for instance regulating immunity, anti-aging, anti-oxidation, anti-tumor, anti-inflammatory, relieving physical fatigue, anti Alzheimer's disease, lowering blood lipid, lowering blood sugar [1–3]. The main physiological active components isolated from Lycium barbarum L. are polysaccharides, carotenoids, flavonoids, alkaloids, organic acids, etc. [4, 5]. These active ingredients are widely applied in food and medicine.
Lycium barbarum L., as a raw material with potential nutritional and medicinal value, has attracted much attention. Studies have shown that Lycium barbarum L. played a variety of activities mainly related to its resistance to oxidative stress. Wang et al. investigated the protective effect and mechanism of Lycium barbarum polyphenols on ethanol-induced cognitive impairment in mice. They found that Lycium barbarum polyphenols reduced intracellular oxidative stress level by increasing the expression levels of key proteins and related factors, and ultimately improved ethanol-induced cognitive impairment [6]. Gong et al. compared the inhibitory effects of Lycium barbarum polysaccharides (LBPs) fractions on a variety of cancer cells, including breast cancer cells, cervical cancer cells, liver cancer cells and gastric cancer cells. Then the mechanism of LBPs was studied from cell cycle, mitochondrial function, oxidative stress pathway, apoptosis and other aspects [7]. Therefore, the evaluation of the ability of the main active components of Lycium barbarum L. to resist oxidative stress is of guiding significance to reveal the mechanism of the active components. In addition, the physicochemical characteristics and biological activities of Lycium barbarum L. are affected by many factors [8]. In the research of LBPs, Xie et al. showed that the similar effects of polysaccharides in different regions of China should be related to their similar chemical properties. However, the extent to which they promote macrophage function was different, which might be due to their different active polysaccharide content [9]. Thus, the content of polysaccharide in Lycium barbarum L. from different regions was different, which made the biological activity of LBPs different. Similarly, the content of LBPs may be different in different tree ages, which makes the biological activity of LBPs different, because tree age is a key factor affecting the accumulation of nutrients and active ingredients. Tree age could affect the content of ascorbic acid, total phenol and other active components in fruit juice and the antioxidant activity of fruit juice [10]. Meena et al. studied the effects of three different tree ages of 6, 18 and 30 years on mineral elements, functional components, etc. in Amrapali Mango (Mangifera indica) Fruits, so as to provide mangoes with the most appropriate tree age for people to eat and product development [11]. However, the effect of tree age on the main active components and biological activities of Lycium barbarum L. has not been reported in the same way.
In this paper, as one of the main active ingredients in Lycium barbarum L., LBPs were obtained by the same preparation method from different tree ages, and their total carbohydrate content (TCC), protein content (PC), uronic acid content (UAC), monosaccharide composition, molecular weight distribution were investigated. Their structural characteristics were preliminarily explored, and the role of LBPs of different tree ages in preventing H2O2 induced APRE-19 and CoCl2 induced PC12 oxidative stress was evaluated. It was expected to reveal the correlation between the physicochemical properties of LBPs of different tree ages and their antioxidant effects in order to provide scientific basis for selecting the best tree age of Lycium barbarum L. to separate active LBPs, and thus provide the best source of raw materials for food and medicine with LBPs as the main component.