D. officinale, a traditional Chinese functional food and perennial medicinal herb, has shown great pharmacological activity and economic value in recent years[1, 14]. Due to low natural regeneration rates, habitat destruction, excessive collection and commercial trade, wild resources are on the verge of extinction and cannot meet the growing market demand, so massive commercial artificially protected cultivation has been used to expand production. However, most consumers believe that the quality and efficacy of D. officinale is safer and more effective among the wild collections.. There are a number of factors that affect the overall quality of D. officinale, including temperature, moisture, minerals, and pathogenic bacteria. In the current study, in order to make a comprehensive comparison of D. officinale cultivated by the same species in different environments, we compared the main phytochemical contents between wild planting in Anhui and artificial-sheltered cultivation in Beijing during 3–5 years growing, and we explore the characteristics of nutrient components in a circle of 12 months. In addition, we compared the metabolite characteristics of both cultivated samples at their 5-year planting.
A number of in vivo and in vitro studies have shown that D. officinale has many health benefits, including antioxidant, anti-inflammatory, anti-diabetic, immune enhancing, antibacterial, and others. The proven benefits are attributed to its functional constituents, which mainly include polysaccharides, alkaloids and polyphenols[16–19]. Since D. officinale is a perennial herb, it usually takes 2–3 years for nutrient accumulation to reach the maximum level. Previous studies have shown that the optimum harvesting time is in the third year[20, 21], but few studies have further investigated the properties after 3 years of growth. In this study, we also found that the best harvesting time is in the third year and with the extension of the growth year, the accumulation of nutrients in the stem decreased significantly. Among the major nutrients detected, the contents of polysaccharides, flavonoids and total polyphenol were higher cultivated in Anhui than in Beijing, but the accumulation of alkaloids was much lower in Anhui than in Beijing. This might be due to the difference in hydrogen potential of irrigation water between the two locations. Polysaccharides are the main biological compounds in stems, we found that both collected samples could fully meet the specified requirements of more than 25.0% in the 2015 edition of Chinese Pharmacopoeia. Moreover, our results showed higher polysaccharide contents than previous studies, indicating that artificial cultivation can meet the basic quality requirements in polysaccharide contents. Nutrient accumulation may be closely related to the growing environment. The environmental differences between Anhui and Beijing were shown in Supplementary Table 3, the main difference between the two growing areas are the regulation of temperature and humidity.
Untargeted metabolic analysis has been widely used for a comprehensive comparison of detailed metabolite identifications under different conditions[11, 22, 23]. In our study, a total of 272 metabolites were detected in the current study, and the number of detections was greater than some studies. For example, a work aimed to compare metabolite characteristics between two medicinal Dendrobium found 139 major metabolites from D. officinale. Others found more metabolites after different treatments, for example, one study shows a total number of 529 metabolites based on different cultivation substrates, another found 3,655 annotated metabolites with Ultraviolet-B radiation treatments, indicating that ultraviolet-B radiation helps to the accumulation of active compounds in D. officinale. Although different studies showed significant differences in the number of metabolites detected, this suggests that environmental factors play an important role in the types and amounts of metabolites.
With different metabolites, there may be potential differences in biological efficacy, and the application value may also be different, so specific metabolite analysis could be an important basis for quality control of D. officinale. In the current study, we found 6 significant differences among 10 nutritional classifications when we compared samples from Anhui with Beijing. Among them, the two most up-regulated flavonoids are isorhamnetin-o-gallate and cyanidin chloride, the former is a flavonol and belongs to the group of plant secondary metabolites known as flavonoids, which have been reported for many biological activities such as antioxidant, anticancer, antimicrobial and anti-inflammatory effects. The latter is one of the most abundant types of anthocyanins and has been shown to have antioxidant properties inhibiting nitric oxide production in many studies[25, 26]. Moreover, sinapine was significantly upregulated in Peking samples, which led to significant improvements in energy, lipid and glucose metabolism in animal models[27–30], indicating that sinapine may be an important alkaloid in D. officinale cultivated in Beijing. In future research, the separation and purification of the discovered up-regulated substances and their health effects will help to explore new pharmacological mechanisms from the introduced cultivated D. officinale.
The main advantages of the current study include the following: First, the comparison of the accumulation of nutrients under different growing years (3-year, 4-year, and 5-year) between cultivation in Anhui and Beijing was conducted, and the data support that the best harvest time is in the third growing year. Second, the nutritional properties were fully compared in a one-year cycle, and the results show that the accumulation of nutrients is different in different months, and indicate that harvesting must be done according to specific circumstances and nutritional requirements. Finally, an in-depth comparison of the metabolite characteristics of Dendrobium in the two planting areas was conducted, which may provide further support for an in-depth study of biological effects in the future. Moreover, we have some limitations in this study, for example, the environmental factors affecting the accumulation of nutrients should be fully captured and the correlation needs to be analyzed in the future.