Research Progress on the Factors Affecting the Quality of Scutellaria baicalensis Georgi

Jinyue WEI, Ruyue BAI, Xinyuan GAO, Zhe LI, Chunying ZHAO*

1. Key Laboratory of Traditional Chinese Medicine Research and Development of Hebei Province, Chengde Medical College, Chengde 067000, China

Abstract In the production process of Scutellaria baicalensis Georgi, how to improve the quality of cultivated S. baicalensis is the focus of current research. By consulting a large number of relevant literatures of S. baicalensis, combined with the research and production experience of the research group in recent years, the factors affecting the quality of cultivated S. baicalensis were analyzed to provide a certain basis for its rational development, utilization and protection in the future.

Key words Scutellaria baicalensis Georgi, Cultivation, Quality, Influencing factors

1 Introduction

Traditional Chinese medicine Radix Scutellariae, which is the dried root ofScutellariabaicalensisGeorgi, is cold and bitter in nature, and the roots are treated as medicine[1]. Radix Scutellariae has the effects of stopping bleeding, clearing away heat and detoxification, and dispelling dryness, heat and cold dampness[1]. Experimental studiesinvivoandinvitrohave confirmed that Radix Scutellariae extract has good clinical antibacterial and antiviral effects, and does not produce drug resistance[2]. Since the outbreak of COVID-19 in December 2019, Radix Scutellariae extract and other natural extracts with antibacterial properties have attracted people’s attention[3]. Moreover, as a traditional bulk medicinal material, Radix Scutellariae has a large market demand. With the increase in market demand for Radix Scutellariae, the proportion of cultivatedS.baicalensisis gradually increasing, and it is the main source of Radix Scutellariae on the market, while the market share of wildS.baicalensisis getting smaller and smaller[4]. However, the chaos of germplasm resources, imperfect cultivation techniques, and unreasonable use of fertilizers have caused the quality of cultivatedS.baicalensisto decline. In this paper, the effects of germplasm resources, origin, cultivation, fertilization, harvesting, and processing on the quality ofS.baicalensiswill be studied to provide a certain basis for its rational development, utilization and protection in the future.

2 Germplasm resources

Germplasm resources are one of the important determinants of the quality ofS.baicalensis[5]. Germplasm resources are the biological genetic resources ofS.baicalensis, which directly determines its quality and yield. Relatively speaking, the genetic genes of long-term selected and bred ancient and wild germplasm resources are better, and it is easier to breed more resistant and excellent varieties, so they are extremely valuable biological resources[6]. However, the use of old seeds year after year will lead to the degradation of the germplasm of Chinese medicinal materials, and the yield per unit area and quality will decrease. The quality ofS.baicalensisseeds currently purchased on the market cannot be guaranteed[7]. The direct cause of the chaos of germplasm resources is misinformation and misrecognition caused by unclear records of herbal medicines and incorrect identification[7]. The behavior of blindly introducing seeds is also one of the reasons for the chaos of germplasm resources[6]. The determinants of the quality of Radix Scutellariae include germplasm resources, cultivation management, and production methods. The genetic variation ofS.baicalensisis very large. The reasons are that the content of chemical components inS.baicalensisshows significant differences in different populations and production areas, and the yield difference is also large. Based on this, studying the breeding of new varieties based on different breeding methods has far-reaching research significance, such as cross breeding, mixed selection,etc[8]. The most urgent task for the development ofS.baicalensisindustry is the selection of germplasm resources. It is of great significance to strengthen the selection and breeding of improvedS.baicalensisvarieties.

3 Producing areas

The main producing areas ofS.baicalensisare Hebei, Gansu, Shanxi, Shaanxi, Shandong, Inner Mongolia, Henan and other provinces[9]. Among them, Shanxi produces the most. Its genuine producing area is Chengde. The study of Guo Lanpingetal.[10]shows that the suitable growth environment ofS.baicalensisis a cooler place; during the growth and development ofS.baicalensis, it can induce the synthesis of secondary metabolites based on certain adversity stress,e.g.the synthesis of phenylalnine ammonialyase, and flavonoid components are also produced in an adversity stress environment. The climate in Chengde is completely suitable for the growth ofS.baicalensis. The artificial cultivation ofS.baicalensisis mainly concentrated in the northwest, north and northeast of China. It is usually planted in sandy loam and loam, and drainage and light are good. The climatic conditions of wildS.baicalensisare characterized by drought, cold, and strong light, and it grows mostly in hilltop grassland[6]. Through HPLC fingerprint comparison, Wang Danetal.[11]find thatS.baicalensisin Chengde, Hebei Province is the first group of modern genuine producing areas, and it is similar to that in Chifeng, Inner Mongolia. Tian Tian[12]used HPLC fingerprints to detect 22S.baicalensissamples that came from 6 producing areas with different climatic characteristics. The results show that the content of total flavonoids in the wildS.baicalensisfrom Chengde, Hebei is the largest, and the content of baicalin in the annual sample ofS.baicalensisin Weifang, Shandong is the highest, while the content of oroxylin A, wogonin, and baicalein in the biennial sample ofS.baicalensisin Changzhi, Shanxi is the highest. The comparison of the quality of samples from various producing areas shows that relatively high-qualityS.baicalensiscomes from Hebei, Shaanxi, and Shandong. The analysis ofS.baicalensisvarieties in different growth periods in the same production area shows that the quality of annualS.baicalensisis better. Li Huaetal.[13]found that theS.baicalensissamples from Chengde, Hebei Province have the highest content of baicalin and wogonin, and the anti-RSV effect of the water extract ofS.baicalensisin Chengde, Hebei Province and corresponding simulated samples are the strongest.

4 Cultivation techniques

The research and development history ofS.baicalensishas a long history. The resources of wildS.baicalensishave been continuously reduced in the development process year by year. Its supply has been unable to meet the increasing market demand. In recent years, the output of artificially cultivatedS.baicalensishas increased year by year[15]. Meanwhile, the germplasm ofS.baicalensishas been degraded significantly, and the content of chemical components has decreased. The reasons are blind pursuit of yield, self-propagation and self-planting based on the widely promoted asexual cutting technology, and neglecting the selection of improved varieties[14]. In this context, attention should be paid to the research on seed reproduction ofS.baicalensis. Research on standardized breeding and selection is an effective way and method to protect the germplasm resources ofS.baicalensis[15]. Zou Tingweietal.[16]pointed out that compared to convention planting T1, the biomass ofS.baicalensisincreased differently, and the content of active substances inS.baicalensissignificantly increased under the modes of ridge planting T2, ridge planting+nonwovens T3 and ridge planting+covering+nonwovens T4, of which T4 was the most significant, followed by T3. Wang Jingetal.[17]found that under the same fertilization conditions, the diameter and surface area of the roots ofS.baicalensisdecreased with the increase of planting density. It can be seen that reasonable planting density is very important to its yield. Wei Yingyingetal.[18]proposed that applying the film-mulching cultivation model to the cultivation ofS.baicalensiscould improve the quality ofS.baicalensis; compared with bare-field cultivation, the content of baicalin was increased by 17.80%. The study found that soil mulching can effectively improve soil fertility, enhance soil fertility retention and fertility supply, increase soil temperature, increase its supply of available phosphorus and potassium, and promote the absorption of ammonium nitrogen. Therefore, it is very important to improve the cultivation techniques ofS.baicalensis.

5 Fertilization program

5.1 Effects of combined application of nitrogen, phosphorus and potassium on the quality ofS.baicalensisNitrogen, phosphorus and potassium are important nutrient elements in soil, and are indispensable essential nutrients in the process of plant growth and development and accumulation of effective ingredients[19]. The most direct source of nutrients is fertilizers which are rich in nutrients required for the growth and development of a variety of crops. Its direct function is to optimize the physical and chemical properties of soil, thereby improving quality and increasing yield. Therefore, fertilizers are an indispensable part of the cultivation of Chinese medicinal materials[20]. Fertilizers contain various nutrients essential for the growth of medicinal materials, so the fertilizers used will directly affect the quality of medicinal materials. Nowadays, there are nitrogen, phosphorus and potassium fertilizers, compound fertilizers, organic fertilizers and special fertilizers on the market. Chemical fertilizers mainly containing nitrogen, phosphorus and potassium are still the main fertilizers used by people[21]. However, long-term use of chemical fertilizers will cause soil compaction, soil nutrient imbalance and an increase in heavy metal content, which in turn will cause the quality of medicinal materials to decline and even involve the safety of medicinal materials[22]. During the growth and development ofS.baicalensis, its biochemical and physiological processes can be coordinated through rational fertilization. On the one hand, rational fertilization can provide it with a variety of nutrients and increase the accumulation of nutrients. On the other hand, rational fertilization can effectively improve plant resistance to stress[23]. Soil is rich in a lot of nutrient elements and mineral nutrients. The content of different nutrient elements in plants is somewhat different, but they are both indispensable to the growth and development of plants and cannot replace each other. Zhang Xiaohuetal.[24]found that compared with the control group, applying appropriate amounts of nitrogen, phosphorus and potassium fertilizers during the growth and development ofS.baicalensiscould effectively improve the quality ofS.baicalensis. The content of Mn increased by 128.8%, and the content of Fe increased by 106.7%. Cao Xianyangetal.[25]show that the application of nitrogen, phosphorus and potassium compound fertilizers has a better effect of yield increase than the single application of nitrogen, phosphorus, and potassium fertilizers.

5.2 Effects of applying organic fertilizer on the quality ofS.baicalensisOrganic fertilizers have comprehensive nutrients and are released quickly, which can improve the utilization rate of fertilizers. At present, compound fertilizers mixed with organic and inorganic fertilizers are currently the focus of fertilization inS.baicalensis. Yang Yangetal.[26]found that different fertilization modes have different effects on the outcrop cultivation methods ofS.baicalensis. The study shows that the combined application of 2.5 mg/m2of superphosphate, 1.74 mg/m2of urea, 0.57 mg/m2of potassium sulfate, and 150 mg/m2of organic fertilizer could increase the yield by 8% compared with other fertilization methods, and the root length and thickness are all increased. He Xuelietal.[27]combined the experimental analysis method with the pot cultivation method ofS.baicalensis, and found that AM fungal inoculation based on a certain level of P application is beneficial to the improvement of the quality ofS.baicalensisand can effectively improve the utilization of P; replacing P fertilizer with N fertilizer is beneficial to the growth and development ofS.baicalensisseedlings, promotes the accumulation of chemical components in the plant, increases the utilization of N fertilizer, and improves the amount of N fertilizer applied[28]. Zou Tingweietal.[19]found that different fertilizer ratios have different effects on the biological content ofS.baicalensis. Among them, when the ratio of urea∶superphosphate∶potassium sulfate∶plant ash is 2∶10∶8∶80, the fertilizer effect is the best. Compared with other combinations, the content of baicalin and wogonin increases, and seedling height and other biological characteristics also increase.

6 Harvesting and processing technology

Whether the harvest of Chinese medicinal materials is reasonable or not directly affects the yield and quality of medicinal materials, and the harvest time is the most intuitive factor[29]. It is found that the yield of biennialS.baicalensisharvested in autumn is the highest. When it is harvested at different times in the same season, there is a certain difference in the content of baicalin. If it is harvested in the fruit period at the end of August, the effect and quality are the best[19]. From the quality analysis of triennialS.baicalensisin different harvesting periods, it can be seen that its flavonoids change dynamically with the advancement of harvesting time, and September is the best harvesting period[30-32]. Shi Yupengetal.[33]pointed out that based on its thick cortex,S.baicalensisis affected by air temperature and humidity to a certain extent during the natural shady drying process, so that the cortex is green, and the quality decreases. Therefore, the obtained driedScutellariabaicalensiscontains higher baicalin. The driedScutellariabaicalensishas a high hardness and is not easy to slice. In order to effectively save time and energy, it is dried naturally after being harvested and sliced.

7 Differences between cultivated and wild S. baicalensis in quality

At present, the demand forS.baicalensisis increasing, wildS.baicalensisis not enough to satisfy the market, and cultivatedS.baicalensishas gradually become the mainstream. Wang Danetal.[34]selected 63 samples of cultivated and wildS.baicalensis, and performed HPLC fingerprint analysis on these samples. It was found that the HPLC fingerprints corresponding to different samples are similar. Compared with wildS.baicalensissamples, the cultivated samples contain more extracts and baicalin. Liu Hongyuetal.[35]used content determination, thin-layer chromatography, and character identification methods to compare and analyze the respective inspection quality of cultivated and wildS.baicalensis. It is found that the content of baicalin in the wildS.baicalensisfrom Inner Mongolia is the highest, followed by the wildS.baicalensisfrom Shanxi and Shaanxi; for the samples from Inner Mongolia, the content of baicalin in wildS.baicalensisdecoction pieces is higher than that in cultivatedS.baicalensisdecoction pieces. The content of baicalin in all cultivatedS.baicalensisis greater than the regulation of the pharmacopoeia. Li Yunjingetal.[36]found that the content of wogonin and baicalin in cultivatedS.baicalensisis higher than that of wildS.baicalensis, and the quality of cultivatedS.baicalensiswas better than that of wildS.baicalensisas a whole.

8 Processing techniques

The enzyme activity of differently processedS.baicalensiswill change, so the chemical composition is quite different. It can be seen that the processing technology is also closely related with the quality ofS.baicalensis. Liu Yanetal.[37]detected the content of various components in raw scutellaria, wine scutellaria, scutellaria charcoal, and fried scutellaria, and found that the content of total flavonoids and baicalin is the lowest in scutellaria charcoal, but the highest in raw scutellaria; the content of baicalein is the lowest in raw scutellaria, but the highest in scutellaria charcoal. Chen Yingetal.[38]analyzed the multi-level infrared characteristic spectra of scutellaria charcoal, wine scutellaria, and raw scutellaria pieces, and found that the characteristic absorption peaks of each one-dimensional infrared spectrum have relatively high degree of similarity; the characteristic absorption peaks of the two-dimensional infrared spectrum have shifted. It can be seen that after charcoal frying, its flavonoids are destroyed, and its total content is significantly reduced. Cuietal.[39]found that the fractal dimension decreases, and the total surface area ofS.baicalensisincreases after stir-frying with wine, and the solubility of total flavonoids and other major compounds increases, and the amount of active ingredients extracted is increased to enhance the anti-migraine effect. Ge Xiuyunetal.[40], detected the content of baicalin inS.baicalensisdecoction pieces obtained by different processing methods by using HPLC chromatography. It is found that the measured index results are different, and the content of active ingredients inS.baicalensisdecoction pieces prepared by baking is the highest, while the content of active ingredients inS.baicalensisdecoction pieces prepared by "secondary processing" is the lowest.

9 Conclusions and outlook

The implementation of the strategy of modernization of traditional Chinese medicine has promoted the transformation and development of the traditional Chinese medicine industry, and the important foundation of the development of the traditional Chinese medicine industry is the resources of traditional Chinese medicine. The content of active ingredients is an important index for evaluating the quality of Chinese medicinal materials and is related to many factors, including processing, cultivation techniques, varieties, and producing areas. Nowadays, the increase in national Chinese medicinal material production support project funds has greatly promoted the development of the Chinese medicinal material planting industry in the direction of "standardization, large-scale production, and production". The main planting problems of medicinal materials include lack of standardization in production, scattered planting, emphasis on production, and no emphasis on technology and management. Although the artificial cultivation ofS.baicalensishas developed rapidly, cultivation methods, fertilization and harvesting are still based on experience, and there is a lack of corresponding theoretical guidance. This will cause problems such as uneven quality and low yield. Therefore, according to local environment, conducting profound theoretical and practical research on the cultivation technology ofS.baicalensis, strengthening the selection and breeding ofS.baicalensisand the development and promotion of special fertilizers is of great significance and is the focus of current development.