Hearty recipes for health: the Hakka medicinal soup in Guangdong, China

Background The Hakka are a subgroup of the Han Chinese, originally from northern China and mainly living in southern China now. Over hundreds of years, the Hakka have developed their own medical practices to prevent and cure diseases, such as medicinal soup, an important characteristic of Hakka cuisine. This study aims at documenting plant taxa used to make Hakka medicinal soup, along with their associated ethnomedical knowledge. Methods Data on Hakka soup-making plants were collected through key-informant interviews, semi-structured interviews, participatory field collection, and direct observation. The choosing of participants has followed the snowball sampling method. Herbs used for preparing medicinal soup were purchased on the local market or collected from the wild, and voucher specimens were collected and identified. The study result was also compared with published studies on soup-making plants in other parts of Guangdong province and the Hakka areas in Fujian Province of China. Results Eighty-three taxa belonging to 70 genera within 38 families were listed by our informants as being used to treat 55 kinds of health problems. Most documented plants are herbaceous species, followed by shrubs and woody liana. Roots were the most frequently used plant parts for medicinal purposes, followed, in descending order, by the whole plant, rhizomes, and flowers. Most plants used to prepare medicinal soup are wild-harvested (56 species), 4 cultivated, and 23 wild harvested or cultivated. According to the comparison, 18 Hakka medicinal soup species are shown both in Fujian Province and Guangdong Province. The Hakka soup-making plants in both provinces share very similar therapeutic functions. This study helps to extend the Hakka menu in both provinces. The study comparison also showed a big difference in the herb ingredients between Guangdong Hakka medicinal soup and Cantonese slow-cooked soup. Conclusion Hakka medicinal soup is an important feature of the Hakka dietary culture. More studies are needed to be undertaken, especially on the efficacy and safety of this medicinal soup. Moreover, cultivation and conservation efforts are required to ensure the sustainability of the species that are used as ingredients in the soup. Consequently, further commercial development of medicinal soup should be promoted.


Background
The traditional food system has played an important role in daily food consumption and health care worldwide, especially in third-world countries [1]. However, some traditional knowledge about practicing the traditional food system has experienced a threat of disappearing due to fast urbanization and modernization [2]. When the pandemic COVID-19 has attacked the world since the Open Access *Correspondence: luobins@lsbg.cn 3 Lushan Botanical Garden, Jiangxi Province and Chinese Academy of Sciences, Lushan 332900, China Full list of author information is available at the end of the article end of 2019, the practice of traditional food systems has re-obtained attention because the indigenous community has shown a series of self-response against the food and medicine shortage during the pandemic time [3]. Therefore, the traditional food system is an important safety buffer providing the indigenous people with natural energy sources and extra nutrition in daily life against the consequences caused by big disasters. The relative traditional knowledge is also worth studying and protecting by the world nowadays.
With the development of the global economy, people have better living conditions, the requirement for food became not just to satisfy the survival needs but also to maintain human health [4]. Thus, the "green", "natural", "medicinal" and "organic" food are pursued by people [5]. The medicinal food plants have thus become a new trend for the food system, which is usually used by indigenous communities for daily health promotion [6]. Since ancient times, China has traditionally used food for health care [7]. For instance, when having a Chinese hotpot ("Huo Guo"), people always like to add different traditional Chinese medicines into the pot for health care purposes [8]. Typically, some people process the medicinal plants into a beverage like tea or medicinal soup, which is very common in the south of China. For example, in the Guangdong Province of China, the culture of cooling herbal tea is extremely popular locally; in the Chaoshan area of Guangdong Province, a study case by Li et al. has reported that more than 186 plant taxa can be used to make herbal tea [9].
As the focus of this paper, the famous diet therapy culture of the Hakka people in China is also a great example of the traditional use of medicinal food plants. The Hakka means "guest families". Hakka people are widely considered to be a subgroup of the Han Chinese, originally migrated from northern China in 300 A.D. to avoid war and natural disasters [10,11]. According to the statistics, more than 45 million Hakka people live in China [12]. The soup made by medicinal food plants is the most typical dish for Hakka people, consumed during every meal in Hakka households. The Hakka people commonly used meats like pork, chicken, duck, young pigeon, and fish as soup ingredients. The soup is prepared as follows: one kind of meat, along with a single medicinal herb or a combination, is placed in a clay pot, marmite, or stewing pot, covered with water. The contents are brought to a boil and then simmered for 1-3 h to produce the medicinal soup. The soup is often consumed within households but is also supplied to restaurants as a typical Hakka cuisine. With the spread of Hakka restaurants, Hakka medicinal soup is becoming increasingly popular in non-Hakka areas. Combining meat with medicinal herbs is thought to improve the taste. The addition of the meat removes the bitterness of the herbs and adds a delicious flavor to the soup. Furthermore, according to the locals, experience has shown that adding meat to the medicinal soup reduces the likelihood of adverse drug reactions. There have only been a few studies on Hakka medicinal soup until now.
One of our former studies in the Hakka area in Fujian Province has reported 42 plant taxa for medicinal soup, which has played an important role in local people's daily lives [13]. A study by Au et al. revealed that there is also plenty of traditional knowledge about medicinal plants in the Guangdong Hakka area, including medicinal soup consumption [12]. Guangdong Province is one of the main habitats of Hakka people in China, with the biggest Hakka population compared to other provinces in China. According to the field trip, we also found that local Hakkas drink medicinal soup every day. Thus, we hypothesized that (1)  In order to verify our hypothesis, an ethnobotanical study was carried out in the Guangdong Hakka area during 2019-2020, aiming to (1) investigate and record the traditional knowledge about medicinal soup in the Guangdong Hakka area; (2) analyze the inventory of the medicinal soup-making plants in Guangdong Hakka area and compared to the study result in the Fujian Hakka area. Additionally, we would like to discuss what kind of role this knowledge plays in the local community, especially during the COVID-19 pandemic. We hope the findings can contribute to the further protection and the future application of related knowledge about traditional soup-making plants.

Data collection
Field surveys were conducted in 2019 and 2020. A total of 213 informants were interviewed, of whom 127 were male and the rest 86 were female. Everyone who participated was informed of the nature and the purpose of the project. Special care was taken in selecting informants. All the informants were Hakka, and only those familiar with medicinal herbs were considered and chosen by the snowball sampling method [15]. The key informant interview method was also used.  [16,17]. The inventory about soup-making plants in this study was also compared quantitatively to the study carried out in the Fujian Hakka area [13]. The similarities, differences between the soup-making plants in two Hakka areas were analyzed.

Plants used as ingredients of Hakka medicinal soup
Altogether, 83 taxa (including four varieties) used for medicinal soup were listed by our informants. Most of the species are widely distributed, and only seven species are endemic to China, including Alyxia sinensis Champ. ex Benth., Polygala fallax Hemsl., Salvia prionitis Hance, Schizostachyum dumetorum (Hance) Munro, and Taxillus sutchuenensis (Lecomte) Danser. All taxa recorded belong to 70 genera within 38 families (Table1). Five species were pteridophytes, and the rest were spermatophytes. Leguminosae was the most represented family (13 species), followed by Compositae (7 species) and Rubiaceae (6 species) (Fig. 2). The taxonomic distribution fully indicated the diversity of Hakka soup-making plants in Guangdong Province. The majority of the documented soup-making plants are herbaceous species (40 species,   Fig. 3. Roots (26 species, 31.3%) were the most frequently used plant part for medicinal purposes, followed, in descending order, by the whole plant (25 species, 30.1%), rhizomes (5 species, 6.0%), and flowers (4 species, 4.8%). The vast majority of the plants are dried (76 species) because it is easier to restore in a long period in such a humid and warm environment; more importantly, dry plants can somehow reduce the strong original flavor and make the locals easier to accept. For example, the Houttuynia cordata is one of the most popular food in the Southwest of China, where the locals usually eat its root freshly, whose flavor is too strong for a lot of outsiders [18]. However, the dry Houttuynia cordata, consumed by Hakka, has a much less strong flavor, not covering other ingredients' taste.
Most plants used to prepare medicinal soup are wildharvested (56 species), four species are cultivated, and 23 are either wild-harvested or cultivated. Thus, more than half of these taxa cannot be cultivated. The wild-harvested plants are collected from forests, hillsides, roadsides, or wastelands nearby the communities.

Medical functions of herbs used in Hakka medicinal soup
The 83 species for medicinal soup are used to treat 55 kinds of health problems. The functions of the herbs used in the medicinal soup are shown in Fig. 4 (category/frequency > 10). Most of these are used for disease prevention or treatment of ailments. The most common uses recorded in this study, in descending order, were: clearing heat (43 species), dispelling dampness (31 species), relieving toxicity (24 species), and dispelling the wind (19 species). These medicinal functions are closely related to the local natural environment and local Hakka livelihood. The Hakka medical system is closely similar to the traditional Chinese medicine system because historically, as a branch of Han people, Hakka people migrated from the main habitat of Han people at that time. The "heat" does not just mean the "high fever" or "high body temperature", and it is more like an unbalanced of the inner energy. Additionally, the "toxicity" we mentioned here is not just from animals like poisonous insects or snakes; it is the unbalance or unhealthy substance accumulation caused by unusual factors like extreme weather, miasma, etc. Local areas are in mountainous topography associated with the very heavy miasma and humid subtropical climate [13,14]. Thus, the medicinal soup for clearing inner heat and detoxication is popular locally. Local livelihoods are mostly practicing agriculture, which is heavy physical labor. In such a humid mountainous area, rheumatism is frequently happened, which is related to the "dampness" and "wind" mentioned above. Thus, clearing dampness and clearing wind are also popular locally.
In addition, some of the herbal ingredients of the medicinal soup have specialized functions that apply to particular categories of people. For example, according to the locals, Artemisia argyi, Melastoma dodecandrum, and Taxillus sutchuenensis are used to prevent pregnant women from aborting. Preparations of Lespedeza cuneata, and Uraria crinita are used to treat infantile malnutrition.
Before introducing modern medicine, some medicinal soups were important mainstream remedies for different health conditions locally; some are still popular [19]. There is scientific evidence that some of the components of chicken soup inhibit neutrophil migration [20]. This biological reaction may be linked to an anti-inflammatory effect that could hypothetically lead to a temporary

Comparison with surrounding areas
Guangdong Hakka region is geographically close to the Fujian Hakka region, and they both share almost the same climate and floras [10]. Consequently, the Hakka communities in both regions share a very similar culture and even the same origin [10]. Thus, we compared this study with our former one in the Fujian Hakka area, which used the same method and was published in 2019 [13].
According to the comparison, as shown in Fig. 5, both studies share18 species of soup-making plants and have the same usages in both areas due to the medicinal properties and the similar Hakka culture. However, 65 soupmaking plants were not mentioned in the study on the Fujian Hakka area, which also indicated the differences in both Hakka areas. The differences could be due to the mountainous topography that cut off the communication between both areas in history. The vernacular names for soup-making plants also show many differences between the two studies. The dialects in two close counties   developed some differences even though mostly similar because the traffic is difficult locally in the history. On the other hand, the amount of Guangdong Hakka soup-making plants is much more than in Fujian Province, which could be due to the impact of other medicinal soup cultures in Guangdong Province. Not just in the Hakka area, medicinal soup is also popular in other parts of Guangdong province, like the Chaoshan area.
Even though the soup-making plant taxa in both Fujian and Guangdong areas showed many differences, we still find, in the level of medicinal function, both soup-making plant inventories share almost the same quality: clearing heat, dispelling dampness, relieving toxicity, and dispelling the wind. The similarity fully indicates that both Hakka areas share very similar environments, climates, and daily livelihoods. However, a similar environment means similar plant distributions. Additionally, except for the endangered species, the plant inventories on both Hakka areas are all ubiquitous species. Thus, the study result can help broaden Hakka cuisine's daily menu in both Hakka areas.
"Lao Huo Liang Tang", which means Cantonese slowcooked soup (CSCS), is famous in Cantonese cuisine and culture. Although CSCS is popular in Guangdong Province, it is not a Hakka cuisine. Liu et el has systematically studied the CSCS using ethnobotanical methods [21]. We also compared our inventory with the one published by Liu et al. [21] (Fig. 6). As a result, both studies only share 11 species in common. Additionally, the CSCS aims for a different medicinal purpose, like around 30 species are used for tonifying Qi or tonifying Yan, by following the classic traditional Chinese Medicine (TCM) theory. Also, CSCS uses more commercialized plant ingredients or the ones common in TCM like ginseng, Amomum villosum, Eucommia ulmoides, etc. The areas that consume slowcooked soup in Guangdong are more developed, while the Hakka communities are in mountain areas with less developed economies and transportation. The comparison indicates a very big difference between Cantonese culture and Hakka culture.

Commercialization and sustainability of Hakka medicinal soup
According to our findings, some medicinal species are under threat as a result of modernization and industrialization processes, leading to habitat destruction and excessive exploitation. For example, the IUCN Red List of Threatened Species lists Pholidota chinensis as near threatened (NT), Gastrodia elata as vulnerable (VU), and Dendrobium officinale as critically endangered (CR). In the China Species Red List, Callerya speciosa (Champion ex Bentham) Schot and Kadsura coccinea are listed as VU; Alsophila spinulosa is listed as NT, and Anoectochilus roxburghii is listed as endangered (EN) [22] According to the research, raw soup-making plants are sold in local wet markets, herbal stores, supermarkets, and e-stores online, with little or no packaging. Both local people and tourists like to consume herbs for preparing medicinal soup. With the development of e-commerce and the spread of Hakka restaurants all over China, soup-making herbs are consequently in demand in areas outside of Hakka communities. Given the continuously increasing demands for soup-making plants, more and more plant species have been cultivated locally. Cultivation of medicinal plants conserves plant resources and makes their collection convenient and accurate [23]. Examples include Ficus hirta, Gardenia jasminoides, and Rabdosia lophanthoides, cultivated in good agricultural practice (GAP) farms in Yuancheng District, Fengshun County, and Pingyuan County, respectively. Other commonly used herbs previously harvested from the wild, such as Anoectochilus roxburghii, Smilax glabra and Uraria crinita are now being cultivated according to the field investigation. However, the threatened status of wild herbs does not give rise to optimism because the domestication of herbs through farming is not always technically possible. We found that Alsophila spinulosa, a tree fern with a long-life cycle, is under serious threat and very difficult to cultivate during our survey. Cultivated plants are also sometimes considered qualitatively inferior compared to wild ones locally. For instance, wild, dried Anoectochilus roxburghii plants (9,000-28,000 ¥/ kg) are considerably more expensive than the cultivated variety (1,250-6,000 ¥/kg). Consequently, they are overexploited and threatened. The over-exploited phenomenon of Anoectochilus roxburghii is also mentioned in the Hakka area in West Fujian Province. The local supervision department should pay attention to the trading and the protection of those endangered wild plants.