Commonly used Paozhi methods with examples of medicines .
Traditional Chinese medicine (TCM) is one of the most established systems of medicine in the world. The therapeutic formulae used in TCM are frequently derived from aqueous decoctions of single plants or complex multicomponent formulae. There are aspects of plant cultivation and preparation of decoction pieces that are unique to TCM. These include Daodi cultivation, which is associated with high quality medicinal plant material that is grown in a defined geographical area, and Paozhi processing where the decoction pieces can be treated with excipients and are processed, which may fundamentally change the nature of the chemical metabolites. Therefore, a single plant part, processed in a variety of different ways, can each create a unique medicine. The quality of TCM materials, their safety and therapeutic efficacy are of critical importance. The application of metabolomic and chemometric techniques to these complex and multicomponent medicines is of interest to understand the interrelationships between composition, synergy and therapeutic activity. In this chapter, we present a short history of TCM, detail the role of Daodi and Paozhi in the generation of therapeutic formulae and look at the international practices and methodologies currently in use to ensure their sustainable production, quality, safety and efficacy.
- chemical fingerprint
- Chinese herbal medicine
- chromatographic fingerprinting
- metabolomic fingerprint
- traditional Chinese medicine
- TCM granules
Traditional Chinese medicine (TCM) has been used extensively for thousands of years  and is the initial medical treatment that the ancient Chinese used to treat wounds and diseases. With the passage of time, Chinese people began to investigate and record the pharmacological activities of the herbs they were using, based on experience. They classified medicinal herbs into five flavours which are pungent, sweet, sour, bitter and salty, forming the earliest system in TCM . As Confucianism and Taoism developed, yin and yang, the five elements (metal, wood, water, fire and earth) and the seven-relation compatibility were introduced and incorporated into TCM. These concepts influenced the development of TCM treatments and therapeutic formulae called Fangji. Fangji are composed of multiple herbs with integrated medical effects and are guided by the concepts underpinning TCM .
Herbal materials used in TCM are often extracted with water to make an aqueous extract or decoction. Single herbs, or multiple herbs combined in one formula, can be used to make multicomponent TCMs. Multicomponent therapeutic formulae are the most important and are most commonly used in TCM for clinical applications . The extraction methods employed to produce aqueous decoctions can vary, depending on the different compositions of the formulae. The details of the extraction methods are important as the methodology can impact the chemicals extracted, and hence, the therapeutic effect of the decoction. In this chapter, we will briefly discuss the historical development of TCM and explain some important TCM theories. Understanding the Chinese philosophy of TCM is of great importance, as this will illustrate why TCM is a very different medical system to Western phytomedicine.
As for all herbal medicinal products (HMPs), the therapeutic effects of TCM are influenced by many factors which affect the quality of the starting materials, for example, quality and age of seed stock, climate, soil, humidity, temperature and sunlight. Factors such as storage, contamination and pollutants can also affect the quality of materials . For TCM, there are some unique traditional practices that can determine the therapeutic activity of the materia medica. These notably include specific cultivation, harvesting, fumigation and processing methods of fresh herbal material, which are keys to the quality, efficacy and safety of TCM. Thus, in this chapter, we will discuss two important traditional Chinese medicine terms called Daodi and Paozhi, both are historical words but are still currently used and play important roles in the development of a TCM .
‘Materia medica’ for TCM decoctions is described as Daodi when cultivated under particular conditions in specific geographic regions and processed with specific methods. In TCM, Daodi medicine is recognised as meeting the highest quality standards and denotes superior clinical properties . Modern scientific research supports the fact that Daodi medicinal herbs are more potent than non-Daodi grown samples of the same herb. These observations are further discussed in Section 2.2. The second key term in the production of TCM is Paozhi, which is defined as a group of methods for preparing TCM to generate material with different clinical or therapeutic purposes . Paozhi methods are guided by TCM theory, and their use differentiates TCM from western herbal medicine. In this chapter, we provide specific examples illustrating this difference. For example, the same herb can be processed in different ways, and Shan zha (Crataegi fructus 山楂), a fruit, is usually fried. This process results in fruit with the generic term ‘Chao’. Different approaches to process the fruit yield different Chao, including Yellow Chao, Charred Chao and Carbonised Chao. The decoctions that result from the different forms of Chao are different in terms of chemical composition, and the resulting decoctions are used to treat different degrees of intestinal disease . Furthermore, processing methods are also very important for the safety and storage of TCM and have a direct impact on the consistency and quality of the Chinese herbal medicine. In general, the variations in quality, safety and efficacy in TCM are the most significant barriers faced by China in gaining access for TCM into European and North-American markets .
Currently, sustainability of ecological resources is attracting global attention, especially for medicinal herbal plants. Since they are in large demand in Asian countries and natural products are gaining in popularity in the European and American markets, there is a major challenge relating to sustainable supply of herbal materials . Thus, cultivation is being adopted to solve the problems caused by wild harvesting. In Section 2.3 ‘Cultivation and wild harvesting’ of this chapter, we will discuss the advantages and disadvantages of cultivation for the sustainable supply of quality herbal materials.
Nowadays, as modern analytical techniques become more sensitive and metabolomic methodologies become more refined, chemometric analysis of TCM is used to investigate the relationship between chemical profiles, candidate components and bioactivities. Multiple methods, such as hyphenated chromatographic and spectroscopic techniques (e.g., liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-nuclear magnetic resonance (LC-NMR)) are applied to determine the chemical fingerprints and to correlate these with bioactivities of TCM. Chemometric techniques advance our understanding of composition and bioactivity of extracts and include, among others, principal component analysis (PCA), linear discriminate analysis (LDA), spectral correlative chromatography (SCC) and information theory (IT) .
The guidance of TCM theory for the generation of Paozhi and therapeutic formulae impacts the chemical composition and final therapeutic effects of medicinal herbs. In contrast, phytomedicine focuses on identification and isolation of individual chemical components, lacking the characteristics of Fangji in traditional Chinese medicine theory, where herbal formulae are organised using the Jun-Chen-Zuo-Shi system. Combining the pharmacological analysis of multiple biomarkers with chemical fingerprint analysis can help to provide an understanding of how the therapeutic effect of herbal formulae is produced .
More recently, modern formulations of traditional TCM decoctions have come on the market. These involve the formation of granulated material, by combining decoctions with excipients and subjecting them to spray drying and granulation to create stable products. Such dried decoction material can also be incorporated into capsules. Modernised TCM formulations are more easily transported and stored and can have a long shelf life than the original herbal material. Some commonly-used TCMs have been formulated in such a way . However, the efficacy of these emerging, modernised TCM formulations has not been fully evaluated by international researchers. In addition, solving the efficacy equivalence between decoction pieces and new formulations is an important problem for the modernisation of TCM .
Therefore, TCM is the final product of several complex factors, that is, TCM theory, medicinal herbs, modern formulations and modern research as detailed in Figure 1.
2. From aqueous extracts to therapeutic formulae
2.1. History of traditional Chinese medicine
Astronomy, arithmetic, agronomy and traditional medicine were the most advanced areas in of science ancient China. Traditional Chinese medicine (TCM) is one of the oldest medical treatment systems worldwide, with thousands of years’ history. It encompasses herbal medicine, animal medicine, acupuncture, moxibustion [a TCM therapy which uses dried Mugwort (or other herbs) burnt on or near the skin to promote healing], therapeutic massage, food therapy and physical exercise . Today, TCM is still used in China and other Asian countries, such as Japan, Korea, Singapore and Malaysia. TCM is one of the most significant alternative treatment systems known and is now increasingly accepted and more widely used by the Western world. In the 2009 Health Department of Taiwan report, it is stated that approximately 28% of the population over 15 years old have used TCM treatment at least once . One key example is the treatment of Alzheimer’s disease using TCM such as Ji-Sheng-Shen-Qi-Wan, Ma-Zi-Ren-Wan and Tian-Wang-Bu-Xin-Dan. These medicines are commonly used to treat mental disorders and nervous system diseases, including Alzheimer’s disease . A clinical trial on the pharmacological activities of Tian-Wang-Bu-Xin-Dan shows that it can reduce the level of interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-α) from elderly dementia patients with sleep disorders, thus demonstrating a measurable effect on biochemical markers .
In ancient China, the effect of many medical materials was identified by tasting, and the taste of herbs was classified into five flavours (pungent, sweet, sour, bitter and salty), with each flavour representing different drug properties . Over time, people learned more about the healing properties of herbs and learned how to use them for treatment of different diseases; for instance, Coptis chinensis (Huang lian黄 连), which is known to have a bitter taste, was used to treat diarrhoea . In Yan Di’s legend, Shen Nong organised the tasting of hundreds of herbs and often recorded poisonous effects. Thus, great knowledge of activity and toxicity was accumulated, and following many trials, the applications for efficient medicines were recorded and summarised, resulting in the earliest recordings of TCM (Figure 2). Two of the earliest Chinese medicine books, the ‘Huang-Di-Nei-Jing’ (770–221 BC) and the ‘hen-Nong-Ben-Cao-Jing’ (25–220 AD)  had great influence on the TCM development in the long history of China .
Decoction of herbs, the most important preparation method of Chinese medicine, was first invented and further developed between 2000 and 474 BC. The medical ingredients were extracted by boiling in water or alcohol, with special preparation times that depend on the properties of the ingredients. Following this, the decoction was filtered, and the resulting liquid was taken by patients. In modern China, the method of decoction is still the most commonly used process in TCM .
In TCM, most of the disease diagnosis and principles of medical application are based on a particular Chinese philosophy that is aligned with Confucianism and Taoism . The theory of TCM refers to Yin and Yang, the five elements, zangfu, channels-collaterals, qi, blood, body fluids, methods of diagnosis, differentiation of symptom-complexes, etc. Yin and Yang are opposite and complementary sides of the nature in the universe, and, according to Chinese philosophy, everything could be described by Yin and Yang (Figure 3) . In TCM, Yin refers to the material aspects of the organism, and Yang refers to functions. It is the interpretation that the disease is caused by the imbalance of Yin and Yang in the human body. The rationale of Chinese medicine is to bring Yin and Yang back into balance, which results in overall health and cure versus the disease .
In addition, in ancient Chinese theory, everything in the universe consists of five elements (metal, wood, water, fire and earth) (Figure 4). All organs and tissues were assigned to different elements, which are differentiated by their properties . This is the special Chinese system theory that forms a basis for TCM. Chinese medicine is very different from Western medicine, and the methodology of disease treatment cannot be explained in the same way as in modern medicine, as it is a type of treatment that is based on experience and a special philosophy .
After the 1950s, advanced research into TCM began, which was aimed at meeting the needs of the growing Chinese population and also at reaching the standards of safety, efficacy and quality of Western medicine . In the 1970s, Youyou Tu was inspired by a book about TCM, the ‘Zhou-Hou-Bei-Ji-Fang’ (317–420 AD), in which Artemisia carvifolia (Qing hao 青蒿) was described as being extracted with water to produce a decoction, and this was used to treat malaria symptoms. This led her to isolate artemisinin from the Qing hao plant. Artemisinin was successfully tested for the treatment of epidemic diseases including malaria in China, which ultimately led to Youyou Tu to being awarded the Nobel Prize in 2015 .
With the passage of time, TCM was also delivered in increasingly diverse formulations, other than decoctions, such as wines, pills and plasters. Currently, modernised formulae such as granules, oral liquids, capsules, dissolved medicines and ointments are coming onto the market. These modern formulations are produced by a small number, currently six, of State approved pharmaceutical industries . China introduced the concept of ‘internationalization of TCM’ in 1996, to address sustainable production and to promote export and international trading, and as a result, the quality, safety and regulatory requirements for TCM have gained increasing international attention and have promoted the formation of international consortia (e.g., GP-TCM;
2.2. Daodi herbal medicine
Daodi is a term unique to TCM and is reserved for medicinal plants cultivated in a specific geographical area with specified natural conditions and being harvested and processed following standards. ‘Dao’ refers to the measurement unit of districts in ancient China, and ‘di’ refers to earth, land or soil. It is stated in an ancient materia medica ‘Xin-Xiu-Ben-Cao’ that the medical efficacy will be different if the medicinal material is not grown in its native environment . Daodi medical material has been regarded as superior medicine for centuries and is recognised as such by today’s TCM pharmaceutical industry (Figure 5). From the author’s observation of Daodi Houttuynia cordata and non-Daodi Houttuynia cordata plant material, the Daodi material is more vibrant and less dense. In the Chinese Pharmacopoeia (2015), 284 different kinds of TCM plant materials are recognised to have Daodi specifications from a total of 584 commonly used medicinal plants .
TCM knowledge and expertise have grown over millennia of clinical experience, resulting in the discovery and understanding of the differing properties of herbal material, which depend on their quality, and often are impacted by the source. The earliest description specifying certain regions for medicinal plant production can be retraced to the late Eastern Han Dynasty (25–220 BC) and was recorded in the ‘Shen-Nong-Ben-Jing’ (Figure 6). The book states that the properties of medicinal plants vary from region to region . In the Ming Dynasty (1368–1644 BC), the Daodi concept was initially described in the Materia medica ‘Ben-Cao-Pin-Hui-Jing-Yao’ .
At that time, the detail relating to the production region was recorded by very simple and basic descriptions, for example, ‘grows on mountain valleys, river valleys or marshes’. With increased experience and accumulated knowledge, ancient people started to name some medicinal plants by the names of regions, for instance, Radix Morindae officinalis (Ba ji tian 巴戟天) or Crotonis fructus (Ba dou 巴豆) . ‘Ba’ was the name of a Sichuan province, hence the Daodi region of Ba dou and Ba ji tian is Sichuan. In 420 BC, it was stated clearly in the book ‘Ben-Cao-Jing-Ji-Zhu’ that the term ‘Zui jia’, which means ‘the best’ in Chinese, should be used to describe the appearance and quality of plants grown in specific regions. Later, in the Tang dynasty, the term ‘King of Medicine’ was applied to describe the best medicine which is recorded in the book ‘Bei-Ji-Qian-Jin-Yao-Fang (Qian-Jin-Fang)’, and shortly after, Sun simiao in his book entitled ‘Xin-Xiu-Ben-Cao’ created the term Daodi .
In ancient times, Chinese people found that the taste of mandarin which was produced south of Huai River were sweet; however, mandarins that were produced in the north of Huai River were bitter. Although the leaves and appearance were similar, the flavour was completely different. Thus, ancient Chinese people were aware of the fact that geographical changes may influence the activity of herbal material used in TCM . The characteristics of plants are determined by genetics; however, the diverse landforms and weather in China resulted in different ecosystems, which contributed to a variety of botanical germ plasm origins . Additionally, specific ecological conditions such as topography, soil, climate, humidity and light also influenced the number of secondary metabolites of plants, which resulted in different bioactivities of a particular herbal material. Therefore, the combination of the geographical location and the specific germ plasm resulted in the superior quality of the Daodi medical material .
In the first modern monograph of Daodi medicinal material in the Chinese Pharmacopoeia (1953), 159 different medicinal materials are classified into 8 categories according to the various production regions in China (Figure 7): Chuan (Sichuan), Guang (Guang dong/Guang xi), Yun (Yun nan), Gui (Gui zhou), Nan (Southern China), Bei (Northern China), Zhe (Zhe jiang) and Huai (He nan). Interesting examples include Liguisticum chuanxiong Hort. (Chuan xiong 川芎), which belongs to Chuan Daodi medica material, because the Sichuan province is the native region for cultivation and is known to have the largest output and longest history of medical application of Chuan xiong. Liguisticum chuanxiong Hort. cv. Fuxiong (Fu xiong 付芎) is produced in the Jiangxi province and has large and fleshy rhizomes similar to Daodi Chuan Xiong; however, it has been shown that it contained less essential oil by chemical analysis, which resulted in different bioactivities . Ginseng is one of the most famous and expensive TCM plant materials, and the Daodi production region of ginseng is in North-Eastern China. In 1958, ginseng was cultivated on the Hailan island in Southern China, which resulted in large roots which were lacking bioactive constituents . In the past 10 years, chemical constituents of volatile oil in the rhizomes and radices of Notopterygium incisum Ting (Qiang huo 羌活) from different regions were investigated by GC. In the Sichuan Daodi sample, 769 compounds were identified and quantified and showed significant differences in the chemical composition of samples that were produced in other non-Daodi geographical regions .
Nowadays, with the increased need for herbal medicines for health purposes, including food supplements, nutraceuticals and skincare products, it is recognised that the Daodi region cannot produce sufficient plant materials to meet the market demand . Since 2002, the Chinese government is emphasising Good Agricultural Practice (GAP) for the cultivation of medicinal materials, which is aimed at expanding the production regions. According to the Good practice of TCM report of the European commission in 2012, Daodi medicinal herbs and also new Daodi medicines will be allowed to emerge . For instance, Daodi Radix Salviae miltiorrhizae (Dan shen 丹参) that was cultivated exclusively in Sichuan, is now produced on large-scale standardised plantations in the non-Daodi region Shanxi province by modern TCM pharmaceutical companies . The Tasly pharmaceutical company was the first, approved by GAP, in China for the large-scale standardised plantation . Goji (fruits of Lycium barbarum L. and Lycium chinense Mill), which has been applied in TCM treatment for millennia to treat imbalance of yin, is now experiencing an increased demand as it is also seen as ‘super food’ and recommended as potent antioxidant in the Western world [44, 45]. The Ningxia province is recognised as the Daodi region for Goji, but the increasing market led to new cultivations in other regions such as in the Hubei, Qinghai and Xinjiang province, where the geographical and climatic conditions are different to the Daodi region. Goji produced from those regions also has very high quality, but is different in the number of metabolites, such as polysaccharides, flavonoids, betaine and carotenoids  Therefore, it is still challenging to achieve the aim of GAP. In Yao’s group, the antioxidant activities of Daodi Goji and non-Daodi Goji were studied, and the IC50 values of the radical-scavenging effect for both Goji treatment groups were determined to be even higher than the positive control group which was treated by Quercetin. Notably, the Daodi Goji shows the highest anti-oxidant activities of all tested materials in this study .
Daodi medicinal material plays an essential role in TCM treatment, but its superior quality has not yet been adequately explained by modern science . Comparisons between Daodi and non-Daodi materials have been studied mainly in terms of bioactive ingredients or composition, soil properties, the geological background system (GBS) and some identification methodologies to assess Daodi attributes, which might be closely related to bioactive ingredient production . However, the superior quality, safety and efficacy of Daodi products still remain to be investigated. Current research of Daodi products focuses on the identification and authentication of species in the Daodi region, establishment and implementation of the commercial specification criteria and standardisation of plantation and processing . Therefore, there is a need for further research in TCM to establish many factors that influence the potency of Daodi medical material.
2.3. Cultivation versus wild harvesting
China is reported to have the largest number of medicinal herbs, with approximately 11,146 being used in 2016 . TCM is based on wild medicinal herbs resources, and it was stated in 2015 that they account for approximately 80% of the total Chinese herbs resources . To meet the increasingly higher demands from the domestic and global market and also to achieve the sustainable utilisation of medicinal herbs, some scale-up cultivation projects for TCM herbs have been established . Moreover, natural foresting, which is closer to wild harvesting but different to conservative artificial cultivation, is recommended to be applied for production of some medicinal herbs, such as Fritillaria cirrhosa (Chuan bei mu 川贝母), Radix Ginseng (Ren shen 人参) and Huang lian, but the cost is much higher than that of cultivation . It is anticipated that cultivation of medicinal herbs will satisfy the market demand and reduce the ecological pressure caused by wild harvesting. Outcomes for cultivation show that it is an approach suited to some herbal material, and the appearance and efficacy are very close to herbs harvested wildly. However, high upfront costs can be associated with the construction of the special environment needed for mass cultivation, but the economic and ecological benefits of cultivation versus wild harvesting are recognised .
However, the consistent quality of herbs from artificial cultivation and wild harvesting is still a challenge for most TCM herbs, because quality, safety and efficacy of medicinal herbs can be impacted by variations in cultivation. For example, the active components of Ranunculus ternatus are polysaccharides, and the concentration of which varies significantly between samples collected by natural fostering and wild collection, 10 and 14%, respectively . To solve the problems of artificial cultivation, standard operating procedures, which include germ plasm selection, breeding, fertilisation, irrigation, pest control and limitation of toxic substances, are required to improve the quality of TCM close to that of the wild harvested herbs . In the ‘Guidelines for Good Agricultural Practice of Chinese Crude Drug’, the GAP standards for four medicinal herbs, Ginseng, goji, Radix glycyrrhizae (Gan cao 甘草) and yu xing cao are described in detail .
Cultivation and wild harvesting have advantages and disadvantages. For cultivation, soil fertility has a significant impact on the yield of the major chemical components in herbal materials, and the lack of standards for soil fertility will result in unsure biomass and quality of medicinal herb production. The standards for soil fertility should include soil texture, density, moisture content, soil acidity, nitrogen and phosphorus content and microorganisms. For wild harvesting, the quality of medicinal herbs is determined by factors such as identification, time of harvesting, harvesting methods and transportation. Harvesting methods should avoid damage to harvested material and to surrounding herbs. The ideal quantity of harvested herbal material should be scientifically considered and balanced, to allow for sustainability. The period of harvesting is important as the effective chemical contents of herbs vary seasonally and climatically, which will impact on biological activity of the decoctions derived from the herbal material [50, 55]. The effects of global warming on plant cultivation, sustainability and quality will have to be considered in the coming years, a topic under investigation at Kew gardens (
Wild harvesting can be considered ‘treasure from the nature’, as the material comes from the natural resource without the addition of pesticides. Furthermore, for most of medicinal herbs, wild harvested material is superior, with resultant decoctions being more potent. However, overloaded harvesting causes an imbalance in the ecological environment and threatens the quantities of wild resource of especially rare or endangered species. Codonopsis pilosula (Dang shen 党参), Dan shen, Radix isatidis seu Baphcacanthi (Ban lan gen 板蓝根), ginseng and Coptis chinensis (Huang lian 黄 连) are some of the key TCM herbs cultivated in different regions in China . Without doubt, the management policy and practice of wild harvesting of natural resources require further development, if goals of sustainable supply of this resource are to be achieved.
In conclusion, cultivation of medicinal plant material reduces the ecological impact caused by extensive wild-harvesting and can also protect the standardised genotypes of species, contributing to the sustainable production and utilisation of Chinese medicinal herbs. Cultivation also has an economic benefit, with new industries and employment models emerging, and guaranteeing the supply for the expanding and substantial Chinese and/or global markets. However, one negative impact is that the natural diversity of the gene pool for wild resources is reducing due to the standardisation of mass cultivation practices . A reasonable balance of cultivation, wild harvesting and natural foresting will ultimately be the best model and will contribute to the sustainability of TCM herb resources (Figure 8).
Paozhi is a unique traditional processing technique, which differentiates TCM from Western herbal medicine. The processed products following Paozhi are known as decoction pieces . With the guidance of TCM theory and according to the properties of medicinal plants, the raw herbal medicine is processed to suit the TCM therapeutic purpose . In TCM theory, it is the belief that disease is caused by the imbalance of Yin and Yang, and ancient Chinese people believe that the processing procedure could adjust the ‘Qi’ (heat, warm, cold and cool qualities) of raw herbal medicines , to equilibrate the balance of Yin and Yang in the human body.
Processing methods are usually different for different medicinal plants, and this is due to the nature of the material, for example, radix (root), rhizoma (rhizome or lateral root), herba (herb, whole plant) and flos (flower) and the purpose for their clinical application. The main aim of Paozhi is to enhance the efficacy and reduce toxicity . For instance, Radix Aconiti kusnezofii (Cao Wu tou 草乌头) is processed to reduce toxicity for safe use by steaming or boiling with Radix glycyrrhizae (Gan cao 甘草) and Semen Sojae hispidae (Hei dou 黑豆). Paozhi is also applied to remove disagreeable odours and flavours of medicinal plants, for example, Herba sargassii (Hai zao 海藻 ) is processed by a clear water rinse. Most herbs are sliced, shaved, or chopped, which is favourable for preparation, storage and pharmaceutical production .
The processing mechanism of Paozhi can be explained by a direct reduction of toxic contents and constituents, structural transformation of constituents and influence of excipients (Figure 9). Most Chinese Herbal Medicines (CHMs) need to be processed prior to use in clinical therapy. In the Chinese Pharmacopoeia (2015), decoction pieces and related processing methods are laid out in specific chapters of CHM, and some decoction pieces are recorded with specific quality control standards and indications, such as Radix Astragali membranacei (Huang qi 黄 芪), which helps strengthening the immune response .
The earliest description of Paozhi can be traced back to 200 BC and classic methods, including burning, stewing and soaking with wine and vinegar, were recorded in ‘Wu-Shi-Er-Bing-Fang’ . In the Ming Dynasty (1368–1644 AD), the processing methods according to Paozhi flourished and became more refined and creative as a variety of additional excipients was introduced in herbal medicine processing . Later, in the first monograph of processing methods ‘Lei-Gong-Pao-Zhi-Lun’ (around the fifth century), the Paozhi processing methods of 268 TCM materials were recorded, of these, 178 medicines were prepared with excipients (Table 1). These comply with the theory of ‘seven-relation compatibility’ in the TCM theory system . When two or more herbal TCMs are combined in one formula, the ‘seven-relation compatibility’ is applied, which is very important for Paozhi. For example, ‘xiang wei’ means one herbal medicine can reduce the toxicity of another medicine, thus the toxic herbal medicine Rhizoma arisaematis Preparatum (Tian nan xing 天南星) is traditionally processed with ginger to reduce its toxicity for clinical safety. Studies of chemical changes in processed Tian nan xing showed that levels of calcium oxalate, which is recognised as a toxic substance, were reduced by 50% compared to the raw herbal material . In 1662, processing methods of 439 Chinese medicines were described in the materia medica ‘Pao-Zhi-Da-Fa’. In the Qing dynasty, the monograph of Paozhi method was recorded in the book ‘Xin-Shi-Zhi-Nan’, which encompassed many classic methods from the long history of processing herbal medicines .
Processing is the way that natural medicines are transformed into TCM by physical or chemical methods. Processing also increases efficacy and/or reduces inherent toxicity. The main processing methods encompass a variety of techniques such as cleaning, cutting, crushing, roasting, boiling, baking and stir-frying, with or without liquid/solid excipients . ‘Chao’ means stir-frying in Chinese. Clean and cut materials are stir-fried until a colour change to yellow is observed, or they may be either charred or ‘carbonised’. Carbonised in ‘chao’ refers to decoction pieces that are black on the outside and brown on the inside. These three stages of processing represent a different degree of ‘Chao’ and infer a different medical efficacy. For example, Crataegi fructus (Shan zha 山楂) is used for enhancing digestion, which can be stir-fried into these three stages. Yellow ‘Chao’ Shan zha is usually used to treat indigestion and charred ‘Chao’ Shan zha is used for diarrhoea, whereas, carbonised ‘Chao’ Shan zha is used for gastrointestinal haemorrhage (Figure 10).
‘Zhi’ means stir-frying with liquid excipients. Clean and cut material is stir-fried with a liquid, such as vinegar, salty water, honey, yellow rice wine or ginger sauce, which allows the liquid to be absorbed by the medical material. For instance, Radix Angelicae sinensis (Dang gui 当归) is well-known to invigorate blood circulation in the human body, and this effect is enhanced when Dang gui is stir-fried with yellow rice wine. The chemical analysis of processed Radix Angelicae sinensis shows significant variation of the amount of ferulic acid and Z-ligustilide, and these chemicals are proved to have an effect in anti-platelet aggregation .
‘Zheng’ means steaming, which can alter the properties of a variety of herbal medicines. For instance, Radix polygoni Multiflora (He shou wu 何首乌) is soaked with black bean sauce and then steamed in a non-ferrous container until the colour is changed into brown, then it is sliced into pieces and dried in the sun. The raw He shou wu is used for its anti-malarial properties, while ‘Zhi’ He shou wu has different therapeutic indications including improving the kidney function, hair blackening and strengthening of bones. Pharmacokinetic studies of typical constituents from processed Radix polygoni Multiflora by LC-ESI-MS/MS indicate that the processing method can improve the bioavailability of garlic acid and decrease the absorption of 2,3,5,4′-tetrahydroxystilbene-2-O-β-d-glucoside (PM-SG), resveratrol and emodin in rat plasma .
The different processing methods have varying influences on medicinal herbs, and this contributes to diverse medical activities and reduced toxicity. For example, Radix et Rhizoma rhei (Da huang 大黄 ) is commonly processed by four classical methods which are recorded in the Chinese Pharmacopoeia (2015). This encompasses ‘Sheng’ Da huang (dried raw material), ‘Zhi’ Da huang (stir-frying with wine), ‘Zheng’ Da huang (steaming with wine) and carbonised ‘Chao’ Da huang (stir-frying till carbonised) (Figure 11). Each of these four processed Da huang products has different medical effects. ‘Sheng’ Da huang is often used for constipation in clinical practice, and ‘Zhi’ Da huang is effective for hematemesis, headache and toothache. Chemically, this may be explained by decomposition of conjugated anthraquinones into the corresponding free anthraquinones. ‘Zhi’ Da huang has an effect on constipation; however, the effect is weaker than for ‘Sheng’ Da huang, which enhances blood circulation, and this may result from decreased contents of tannins. Carbonised ‘Chao’ Da huang has an effect on haemostasis for hematochezia and no effect on blood circulation .
Nowadays, the difference between processed and non-processed medicines is studied by modern scientific analytic methods. For example, Radix aconiti (Chuan wu 川乌) is an essential herbal medicine, which has a long history of application in TCM as it has a wide range of medical effects, such as anti-inflammatory and analgesic properties. However, the non-processed Chuan wu is very toxic and induces remarkable neuro- and cardiotoxicity. Chuan wu is processed by boiling and drying . The comprehensive metabolomic characteristics of non-processed and processed samples were investigated by a LC-MS method, which identified specific metabolite changes. In this study, 22 key biomarkers were related to detoxification by processing. Diester diterpene alkaloids (DDA) and toxic monoester diterpene alkaloids (MDA) were identified to be the main components which were reduced by this processing method for Chuan wu . The contents of magnolo and honokiol from Cortex magnoliae Officinalis (Hou pu 厚朴 ) were reduced by 14 and 40%, respectively, after processing by stir-frying with ginger, and the new component gingerol was formed [40, 72]. The solubility of active constituents can be improved to enhance the efficacy by processing, for instance, Huang lian, traditionally used for toothache, liver disease or inflammation and can be processed by stir-frying with wine, vinegar, salt, bile, or Fructus evodiae (Wu zhu yu 吴茱萸). Chemical analysis of processed Huang lian suggests that the contents of alkaloids are different, depending on the processing method but all are higher than non-processed material, and stir-frying with wine leads to the highest contents .
Triterpene saponins were found to be the main bioactive constituents of Ginseng, which has anti-oxidant, anti-diabetic, immunomodulatory, anti-inflammatory and anti-cancer activities . After processing by steaming and drying, the chemical profiles are remarkably different between processed and non-processed Ginseng. The structural transformation of ginsenosides in processed Ginseng, which proved to have more potent bioactivities, contributes to its enhanced efficacy . Solubility is influenced by processing, and by the addition of excipients, such as wine, honey, vinegar, salt water and ginger juice. Excipients may react with constituents in herbal medicines and may have effects on active constituents, for example, it was reported that ginger juice has anti-inflammatory activity itself which contributes to the detoxification effect of processed Rhizoma pinelliae Tematae (Ban xia 半夏 ). Therefore, processing can result in reducing amounts of toxic constituents, structural transformation and solubility improvement of active constituents.
In addition to daodi, Paozhi also plays an important role in TCM in influencing the quality, safety and efficacy of medical materials. There is a continuing need for multidisciplinary research to fully evaluate the effects of these practices, in order to increase the understanding of their impact on the chemical fingerprints of therapeutic decoctions and on the mechanism of action of resultant TCMs . In different regions of China, the processing methods of TCM vary; for instance, white rice wine is commonly used in the Hunan province, but yellow rice wine is used in Fujian, Anhui and Guangxi province. Today, there is still no consistency of processing practice across China. Hong Kong is the international centre of TCM, and most of the TCM decoction pieces in the western world are imported from Hong Kong. It is reported that 66% of 365 kinds of TCM decoction pieces of commonly used TCM are processed locally in Hong Kong, where the processing methods are different to those in the mainland of China. Such differences may result in a Butterfly effect as eluded by Sheridan et al.  and may result in very different therapeutic effects associated with the final TCM. Consistent and standardised processing methods are required for the global development of TCM .
In recent years, the study of Paozhi is focused on understanding and validating the traditional aspect of processing. The chemical profiles of processed herbal medicine are investigated by NMR, GC and LC-MS analysis methods, and metabolomic profiles are studied with chemical markers. In addition, toxicity or side-effects can result from improper processing methods, and therefore, a standardisation of processing methods for TCM is essential. It seems appropriate that in the modernisation of TCM, significant chemical contents and pharmacological indications should be applied as evaluation markers, a quality control standard should be established to reinforce the GMP of processed products, to optimise the process procedure and standardise the quality, safety and efficacy of decoction pieces.
2.5. Seven-relation compatibility
Multiple herbs can be combined in TCM, with up to 20 herbs in one formula, yielding very complex decoctions. Such a complex formula is called Fangji in Chinese, and it is adjusted for each individual patient under the guidance of TCM theory. At times, single herbs are used to prepare decoctions for treatment, and for instance, Radix Astragali membranacei (Huang qi 黄 芪) is used on its own to treat lung disease. The combination of herbs within one formula is under the guidance of the ‘seven-relation compatibility’ (Table 2), which includes the following: ‘mutual accentuation’, ‘mutual enhancement’, ‘mutual counteraction’, ‘mutual suppression’, ‘mutual antagonism’ and ‘mutual incompatibility’ between two herbs. In addition, single herbs can be used under the ‘seven-relation compatibility’ in an ‘individual application’ for the treatment of certain diseases .
Fangji is defined as formulae composed of multiple herbs with integrated medical effects, and it is guided by ‘Jun Chen Zuo Shi’ theory . One TCM formula generally consists of four different kinds of herbal medicine, which is called ‘jun’, ‘chen’, ‘zuo’ and ‘shi’ (Figure 12). Each of them plays a different role within the formula. All of these medicinal herbs work harmoniously together to achieve therapeutic effects and bring the balance of Yin and Yang back to the human body . In the TCM formula theory system, ‘jun’ means the ‘master’ and provides the principal therapeutic effect for the disease; and ‘chen’ represents the ‘advisor’ which functions as the second principal medicinal component, supporting the medical efficacy of the ‘jun’ medicine. ‘Zuo’ represents the ‘soldier’ and is applied to treat associated symptoms or reduce toxicity of the ‘jun’ medicine. ‘Shi’ represents the ‘guide’ which can direct other medicines to the diseased organ or contribute to the harmony of all herbs in the formula . For instance, Radix glycyrrhizae (Gan cao 甘草) is the most commonly used ‘shi’ medicine, since its sweet flavour can improve the taste of formula decoction and enhance the harmony of the combined herbs . For single-herb formulas, the medicinal herb is a ‘jun’ medicine (master medicine), which shows the principal medical effects.
For example, ‘Ma-huang-tang’ is a formula traditionally used to treat inflammatory liver disease and consists of Ephedra sinica Stapf (Ma huang 麻黄 ), Ramulus cinnamomi Cassiae (Gui zhi 桂枝), Semen pruni Armeniacae (Xing ren 杏仁) and Radix glycyrrhizae (Gan cao 甘草) (Figure 13). Ma huang works as the master medicine, which provides the main anti-inflammatory effects in the treatment of lung diseases. Gui zhi works as the advisor medicine and assists Ma huang to function well, which compiles the ‘xiang shi’ (‘mutual enhancement’) from the ‘seven-relation compatibility’. Xing ren is the soldier medicine and enhances the efficacy of Ma huang. Gan cao functions as the guide medicine, which can adjust the properties of other medicines and improve the harmonisation in the formula. The overall efficacy of the TCM formula is a result of the mixture of chemical components in the multiple medicinal herbs . However, it was reported that pure and active components which were separated and purified from single or multiple herbs are different in their chemical profile when compared to traditional decoctions . This may be due to synergistic effects in the complex medicine or to chemical reactions and other changes which may occur during the decoction procedure.
2.7. Formulations of TCM
Decoction is the earliest and most commonly used preparation method in the clinical application of TCM . A TCM decoction is the herbal tea that is made of processed medicinal herbs which are simmered for hours . The preparation of a traditional medicine decoction has multiple steps such as the sequence of boiling the herbal material and different boiling and filtering times. The preparation of a decoction is complex, as it requires experience and often takes considerable time. The herbal ingredients within the formula for decoction can be changed for the individual patient according to the disease. The herbal medicine may include leaves, flowers, roots, bark or fruits, and the procedure of preparation is depending on the part of the herb that is used. It is of concern that in some instances, the quality and stability of herbal material cannot be assured . Also, the unpleasant flavour of a decoction has been a problem for patients for thousands of years. As equipment advances and market demand increases, modern decoctions have become very popular in TCM hospitals, because of convenience . Decoctions have a quick and often complete absorption with good bioavailability . In a modernised decoction method, the medicinal herbs are combined with water and are extracted in TCM decoction machines . Modern formulations also include granules, oral liquids, tablets, capsules and injections. This change in methodology may in fact influence the composition of the final TCM, and this is another area that would benefit from comparative research studies directed at classical and modern decoction methods.
2.7.2. Modern granular formulations
The use of granules has dramatically increased in China since they are easy to handle, store and formulate. The granule made of a single herb is called a single dispensing granule; when made of multiple herbs, it is called a dispensing formula granule . The preparation of granules is included in the extensive process of decoction: they are prepared by decoction or aqueous extraction with the aid of suitable excipients. After being dissolved in warm water, they can be ingested by patients. With the increasing development of TCM granules, international research has focused on whether decoction can be replaced by granules with similar effectiveness and safety . During the procedure of granule preparation, the difference of water extraction, concentration, desiccation and granulation may influence the dissolution and chemical profiles of active ingredients . Thus, this may result in different clinical efficacy between granules and decoction.
Recently, some cases related to the equivalence of effect between granules and decoction have been reported. Indeed, some differences in chemical consistency were identified, which suggest that the efficacy might not be equivalent between both forms of medicine. Ge-Gen-Qin-Lian-Tang is a classic TCM formula for the treatment of inflammatory bowel disease . The comparison of chemical fingerprints of traditional decoction and granules of Ge-Gen-Qin-Lian-Tang was investigated by liquid chromatography-diode array detector (LC-DAD) to ensure the consistency of efficacy. The fingerprints demonstrated small variations among the 20 peaks, but the peak area of puerain, berberine and baicalein from the granule sample was 50% less than that of the decoction . The TCM formula Da-Cheng-Qi-Tang is commonly used to treat digestive disease. The chemical consistency of decoctions of Da-Cheng-Qi-Tang prepared by traditional and modern methods was investigated. Five compounds were identified as chemical markers, an analysis of which established that the chemical fingerprints were not consistent between these two kinds of decoctions. The study showed that the traditional decoction method had a stronger purgative effect due to higher concentrations of rhein and sennosides . Therefore, it is very important to understand the impact of the formulation method on the therapeutic effect of a final granular TCM product.
2.8. Fingerprint-efficacy analysis in TCM
Over the past 30 years, chromatographic and spectrophotometric fingerprinting methods have dramatically improved, and the application of hyphenated techniques such as high performance liquid chromatography (HPLC)-mass spectrometry (HPLC-MS), liquid chromatography-nuclear magnetic resonance (LC-NMR) or gas chromatography mass spectrometry (GC-MS) in the analysis of TCM facilitates the determination of the quality in research and in the pharmaceutical industry . However, quality standards are challenging to establish, because the complexity of potential active ingredients in medicinal herbs is used in TCM. Today, commonly applied models for TCM quality control include conventional methods, such as microscopic, and macroscopic identification and comparison with monographs, chemical fingerprint analysis using thin-layer liquid chromatography (TLC), liquid chromatography (LC), HPLC, gas chromatography (GC), GC-MS, etc., and multiple marker assays.
Chemical fingerprints and bioactivities assay linked with multiple markers is currently recognised to be effective for TCM analysis . The use of known and previously characterised markers for the analysis of constituents is the most popular method for identification and quality control in TCM. For example, the ginsenoside fingerprint profiles are applied for the authentication of Panax species . Moreover, the fingerprint-efficacy relationship of Lycii fructus (Goji 枸杞) was studied by Zhang in 2018. The spectrum of ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) of three batches of Goji was correlated with the biological data using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays. Compounds relating to the antioxidant activity of Goji, such as chlorogenic acid, quercetin and kaempferol, were subsequently identified by analysis of UPLC-MS/MS data .
Because of TCM’s complexity, it is rare that any single ingredient provides the overall evidence for medical efficacy. Chemometric methods, such as similarity evaluation or principal component analysis, are often used to investigate the fingerprint and bioactivity relationship within the TCM . GC-MS is usually applied for the analysis of volatile metabolites, whereas LC-MS is often used to identify and quantify non-volatile components. Hyphenated methods, such as LC-MS can provide information on fragments of constituents, which can help in the elucidation and identification of chemical structures. In recent years, LC-MS analysis has been widely used in TCM due to its high sensitivity, selectivity and generation of specific information . NMR metabolomic profiling is currently recognised as a quick and generic method in the study and quality control of TCM material. For instance, it was reported that the quality control of Radix Angelica Sinensis was studied by NMR profiling , which resulted in observed differences between samples prepared by different methods.
To ensure the consistency of herbal medicine, the concept of phyto-equivalence was developed. Phyto-equivalence is a comparison of the chromatographic fingerprint of a herbal medicine with the profile of a standard reference product. The fingerprint is defined as a characteristic profile, which reflects the overall complex chemical composition of the sample analysed by chromatographic or electrophoretic techniques. Chromatographic fingerprints are accepted by the US Food and Drug Administration (FDA) in applications for new product approvals . In TCM studies, fingerprints could provide a complete set of information of chemical components including the relative quantity of all detectable analytes . Fingerprinting is widely used to authenticate or differentiate between species, geographical regions or processing methods in TCM.
The ‘fingerprint-efficacy relationship’ is a method that associates TCM fingerprints with a specific pharmacological effect . Multiple methods relate chemical fingerprints, such as characteristic peaks, to bioactivities. The ‘fingerprint-efficacy relationship’ investigation procedure (Figure 14) involves finding the appropriate analytical methods for fingerprints, identifying assays for the various bioactivities, using statistical methods to find the fingerprint-efficacy relationship, select candidate components, and validation of the bioactivities of the identified candidate components . For instance, Valeriana jatamansi Jones (Zhi zhu xiangI 蜘蛛香) has a long history of use in TCM to treat mood disorders like anxiety. The ‘fingerprint-efficacy relationship’ was studied by correlating HPLC fingerprints with in vitro and in vivo tests. Four chemical components, hesperidin, isochlorogenic acid A, isochlorogenic B and isochlorogenic C are regarded as multiple biological markers for this anti-anxiety effect .
Principal component analysis (PCA) is a statistical method, which can reduce the number of variables and dimensionality and create principal components (PCs) to explain the variables in original data. PCA is usually combined with cluster analysis, correlation analysis or regression analysis to determine the relationship of fingerprints and efficacy. It extracts data and can remove redundant information to focus on the main factors. PCA is often used together with other chemometric methods due to the lack of a specific quantification mathematical model for variables . For example, Andrographis herba (Chuan xin lian 穿心莲) is well-known in China because of its bitter taste, which is one of the five flavours in TCM theory. The bitter flavour is recognised as relating to the pharmacological effects of Andrographis herba. In Zhang’s group, the chemical components of 30 different types of Andrographis herba and fingerprint spectrum were determined by HPLC, and the PCA was applied to analyse the chemical components relating to bitter taste relating. According to the results from PCA, andrographolide, neoandrographolide, 1,4-deoxyandrographolide and dehyandrographlide were determined as substances responsible for the bitter flavour of Chuan xin lian . Ephedra sinica Stapf (Ma huang 麻黄 ) is commonly applied for rheumatism, asthma, fever and rheumatoid arthritis in China. The significance of the inorganic elements of Ma huang from different geographical regions was studied by using elemental plasma mass spectroscopy fingerprints and PCA, and the study showed that this is an effective strategy to discriminate TCM samples .
The therapeutic formulae used for health maintenance and disease treatment in TCM are often complex mixtures whose chemical fingerprints are influenced by many factors, by the ancient practices of Daodi cultivation, Paozhi processing and Fangji combinations. As TCM undergoes modernisation and seeks increased entry to international markets which present rigorous legislative barriers, the quality, safety and efficacy are under increasing scrutiny.
In addition, there are increasing demands on supply, and attention needs to be focused on sustainable production, including mass cultivation and appropriately structured wild harvesting. It is obvious from ongoing research that the ancient processes, which vary across the land mass of China, influence the chemical fingerprint of the resulting therapeutic formulae, and thus render TCMs with the same name, from different regions, to have different potency.
Going forward, it is important for the scientific community to continue to apply sophisticated methodologies and chemometric analyses toward understanding how the ancient TCM processes impact on the final product and how sustainable practices can be implemented that will lead to standardised therapeutic formulae which reach the international standards of quality, safety and efficacy.
The authors acknowledge The Chinese Scholarship Council and Trinity College Dublin for the co-funding of Jinfan Wang’s postgraduate research.