Health and commercial relevance of Garcinia species: Key scientometric analyses from three decades of research

Garcinia species ( G. indica, G. cambogia, G. kola and G. mangostana ) represent some of the most sought - after herbs globally due to their impressive medicinal qualities, hence the ever - growing interest of researchers in not into these plants. In this study, an extensive bibliometric analysis of the available research outputs on the widely - known Garcinia species was conducted to appraise the progress made and also highlight the future focus of research on the plants. The published articles (original and conference articles) on the selected species from 1991 to 2021 were retrieved from Scopus® database, scrutinized and further analyzed using the VOS viewer software. Over 2000 research outputs were published posting an annual publication rate of 75 articles, which have altogether garnered almost 37000 citations within the period under review. Of the 85 country affiliations on the publications, 5, which include India, Thailand, Nigeria, Indonesia, and the United States have cumulatively contributed two - thirds of the total outputs. The institutions; the University of Ibadan (97), Prince Songkla University (52) and Mahidol University (50) have the most publications revealing their research focus on herbs. However, in terms of individual influence, Prof E.O. Farombi, of the University of Ibadan, led the pack with an impressive 42 publications (1585 citations) on Garcinia kola followed by Prof Y.W. Chin of the Seoul National University, South Korea with 23 publications (452 citations) on Garcinia mangostana . The versatility in the health applications of these species especially as sources for new therapeutics, nutraceuticals or functional food ingredients, has been the main driver of the research within the past three decades. Recent research undertakings have demonstrated the potential industrial uses of herbs in the clothing and petroleum industries and these may dominate the research emphases in the immediate future.


Introduction
The genus Garcinia which belongs to the Clusiaceae family includes about 400 species that are native to Asia and Africa, America, Australia, Brazil, Polynesia and New Caledonia (1,2). Recently, Garcinia species have received considerable attention worldwide from the scientific as well as industrial sectors, and several potential utilities and novel compounds with diverse bioactivities have been reported. These compounds offer numerous opportunities for pharmaceutical companies in the development of new drug leads. They also represent an excellent source of molecules to produce food additives, functional foods, nutritional products, and nutraceuticals for the growing number of natural products companies. The plants of the genus also have applications in petroleum industries and other diverse industrial fields (3). Fruit-yielding Garcinia trees such as Mangosteen (G. mangostana L.), Brindle berry (G. gummi-gutta (L.) N. Bobson. Syn. G. cambogia (Gaertn.) Desr.) and Kokum (G. indica Choisy) are currently gaining commercial, industrial and medicinal importance (4). Edible fruits and vegetables from these Garcinia species play an important role in providing dietary diversity, food security, nutrition and income generation for local communities and the global economy (5).
The presence of HCA in some Garcinia species is linked to increased fat oxidation, anorexigenic effect, and regulation of endogenous lipid biosynthesis (9). Furthermore, gamboge (or camboge) is the exudate from the bark of several Garcinia species and is used as a pigment in Indian murals and European water paintings. Gamboge is also used for colouring wood, leather, metal and dyeing clothes (10).
In South India, G. gummi-gutta and G. indica are cultivated for commercial extraction of a variety of products such as bioactive acids, nutraceuticals, fats and condiments. The latter species was recently reported to augment synthetic lubricants for the reduction of friction and coating of engine parts and surfaces to protect them from wear (11). Its antioxidant and antimicrobial properties have also been reported (12) and when applied in combination with G. cambogia, they enhanced the shelf life of Mackerel fish using a novel icing medium (12). G. indica also inhibited the corrosion of mild steel purportedly due to the presence of cyanidin anthocyanins (13). Furthermore, G. indica oil has a great demand for the preparation of ointments, face creams and lipsticks in the cosmetic industry while its butter has been utilised as a substitute for cocoa butter (14)(15).
G. mangostana also known as Mangosteen is commonly utilized as a functional food and mangosteenbased beverages had a turnover of more than $200 million in 2008 in the USA alone (16). The impressive commercial relevance of the specie stems from its wide applicability ranging from technological and biomedical applications to biomaterial production (17). Xanthones derived from mangosteen have been reported for their wide spectrum of pharmacological and biological properties (18). These properties include but are not limited to antibacterial, antiprotozoal, anti-cancer, antidiabetes, antioxidant and anti-inflammatory activities (19)(20)(21). Some clinical trials have also demonstrated the bioavailability of xanthonerich mangosteen-based supplements and their potent anti -inflammatory and antioxidant effects (22).
G. kola (bitter kola) is one of the most studied Garcinia species. It is highly valued in Africa and used for hospitality purposes during cultural and social ceremonies where the seeds are usually eaten in their crude form as a snack. G. kola is used in African ethnomedicine for prophylactic and therapeutic purposes, especially for inflammatory-related diseases (22). Due to its health benefits, the efficacy and safety of a detox tea containing a mixture of G. kola and other plants (Andrographis paniculata and Psidium guajava) were investigated as adjuvants to the conventional therapy for COVID-19 in a pilot randomized trial (24). G. kola contains bioactive such as flavonoids, biflavanone, benzophenone derivatives (kolaflavones, Garcinia-flavones 1 and 2), and chromanols (garcinal and garcinoic acid). Of these, the biflavonoidkolaviron is the most studied and has great potential for clinical use as an antidiabetic agent because it targets multiple abnormalities in the diabetic milieu, specifically by targeting ROS production, bolstering antioxidants and limiting inflammation (25). Pharmaceutical companies from Nigeria and Cameroon have recently focused on the small-scale production of bitter kola syrups and herbal pastes as herbal remedies and food supplements (3).
In this article, a bibliometric study of the dynamics of scientific research on commercially-relevant Garcinia species was investigated. The selection of these five species is based on their general popularity and commercial importance (as indicated by their footprint on the World Wide Web) and their scientific importance (as indicated by the number of research publications). This bibliometric study is instrumental in identifying topical hotspots, research strengths and weaknesses, information gaps and top researchers for collaborations. The information will inform research priorities, identify new research areas and promote further commercialization of these herbs.

Materials and Methods
The scientific data (original articles and conference articles/proceedings) on the research on the selected Garcinia species published within the past 30 years was obtained from Scopus® database on the 1 st of February 2022. Scopus was selected because it is the largest scientific journal indexing and citation database administered by Elsevier academic publishers (Amsterdam, Netherlands) (26)(27). The data search on Scopus database was limited to research publications from 1 st January 1991 to 31 st December 2021. This time duration was considered as growth in the use of natural therapeutics and products from plant that became prominent during this period. The search command deployed in this study is defined as follows; TITLE-ABS-KEY ("Garcinia kola" OR "Garcinia indica" OR "Garcinia mangostana" OR "Garcinia cambogia" OR "Garcinia gummi -gutta") AND PUBYEAR > 1990 AND PUBYEAR < 2022 AND (LIMIT-TO (DOCTYPE, "ar") OR LIMIT-TO (DOCTYPE, "cp")). The extracted data from Scopus database was carefully checked for correctness and to avoid duplication using Microsoft Excel® spreadsheet (version 2013, Washington, USA). Thereafter, the VOSviewer software (version 1.6.16, Leiden, Netherlands) was employed to establish coauthorship, co-occurrence and co-citation relationships between authors, institutions or countries, as well as the participation of journals in Garcinia research.

Garcinia research publication growth (1991-2021)
In over 3 decades, a total of 2260 original articles and conference publications on the selected Garcinia species (Fig. 2) were indexed on Scopus database and have garnered a cumulative 36880 citations. There has been a meteoric rise in the research outputs from just 7 articles published in 1991 to 184 in 2021 posting an average annual publication of 75 in the three decades under review. The research activities on the species in the second decade in particular, were pivotal, as the global research popularity of the use of medicinal plants as potential preventative medicines for many chronic diseases continues to increase. For example, the top-4 most-cited research articles; (28)(29)(30)(31), were published during this period. These studies explored the health importance of Garcinia species, especially with relation to their antioxidant, antiglycation, biochemical and enzyme inhibition potentials for the management of many diseases. This upward research trend continues into the last decade with the year 2020 being the most productive year to date with 205 published articles. The exponential research growth on these Garcinia species over the years indicates continued advances and interest from the international research community as the quest to find novel natural therapies for lifestyle diseases goes on.

Country contribution to Garcinia research (1991-2021)
Altogether, 85 countries participated in the research on Garcinia species as shown from the clearly-defined affiliations on the publications indexed on Scopus database. Only 10 of these countries published 50 or more research outputs on the subject within this period with India having the most number (396) as depicted in Table 1. Thailand (329), Nigeria (301), Indonesia (273) and the United States (212) complete the top 5 countries with the greatest number of publications on Garcinia research and cumulatively represent about 66.9% of the total publications. However, in terms of citations, the publications affiliated with the United States were cited the most garnering a total of 8119 citations and is followed closely by Thailand (7295), India (6020), Nigeria (5093) and Japan (4878). Thus, the United States, Taiwan and Japan may have the highest country influence on Garcinia research stemming from their superior citation-topublication ratios of 38.3, 37.,0 and 33.0 respectively. The research contributions over the years by these countries demonstrate their focus and investment in discovering effective phytotherapeutic strategies for life-long diseases that have plagued the human race. Asian countries are well-known for their age-long beliefs in herbal medicines for example, the Kampo (Japan), traditional (China) (32), or Ayurvedic (India) (33) medical systems have become widely accepted worldwide. Similarly, folkloric use of herbal medicines for disease management by the indigenous North American population has been documented even before the advent of conventional 'orthodox' medicines. In recent times, there has been an upsurge in the popularity of herbal medicines in the United States which can be associated with the amount of scientific research being carried out in this niche (34). The sway of the influence on Garcinia research by Nigeria in Africa (Table 1), is not surprising as the country is host to the naturally occurring G. kola tree where its seed has been consumed as a recreational snack in cultural settings since times immemorial. The plant was also dubbed "a miracle tree" due to its role as a major component of the traditional medicinal concoctions to manage many ailments such as diarrhea, bronchitis, bacterial infection etc. (35).
this study, VOS viewer was employed to assess the extent of collaboration among the countries that were actively involved in Garcinia research in the last 3 decades.   (nodes) is a function of the number of publication outputs with inward and outward links uniting or departing from the node while the assembly of individual nodes forms a cluster that is linked together by lines to indicate networks of collaborations and their strengths (44)(45)(46). The thickness of links shows the strength of the connections between any 2 nodes in the network (47)

Institutional participation in the research on Garcinia species (1991-2021)
It is important to assess the influence of universities and other research centers on the published outputs on Garcinia species over the last three decades. The institutions with the highest number of publications, citations and most-cited articles within the period under review were presented in Table 2. The University of Ibadan, Nigeria had the most published outputs (n= 97; 22% of top-10) on Garcinia species, predominantly on the potential pharmacological activities of G. kola. These publications have amassed a total of 2437 citations averaging at least 25 citations per article. The most cited article (226 citations) from the institution described the possible use of a bioflavonoid compound (kolaviron) isolated from G. kola seed to ameliorate the liver injury caused by 2-acetylaminofluorene, a chemical carcinogen (48). The University of Ibadan was distantly followed by Prince Songkla University and Mahidol University, both in Thailand with 52 and 50 publications that were cited 822 and 2143 times respectively. The latter university, however, had the most citation/publication ratio posting an impressive minimum of 42 citations per article among the most influential institutions in Garcinia research. Altogether, the top 100 institutions ( Table 2) have published almost 20% of the total publications on Garcinia research within the period under review. The domination by the Asian institutions is also reflective of the emphasis placed by the continent on the research on herbs for health, food and other applications.

Author participation and citation
The contributions of leading authors in selected Garcinia publications in the last 3 decades are presented in Table 3.    (29) while Bagchi D was the overall author with the least number of publications (14).

Co-authorship analysis
The VOS viewer Bibliometric Map of the Co-authorship network of researchers with at least 5 publications on selected Garcinia plant research is shown in Fig. 4. Out of 7704 authors, 195 meet the threshold of individuals that has co-authored at least 10 publications. Each of these authors was grouped into 9 clusters. Authors in the same clusters may have been grouped together based on similarities in their research interests and collaborations. It is important to point out that of these 195, only 60 authors are significantly linked and connected together to form Effects of a natural extract of (-)hydroxycitric acid (HCA-SX) and a combination of HCA-SX plus niacinbound chromium and Gymnema sylvestre extract on weight loss (61) 140 Table 3. Author participation-Top 10 authors with highest publications on selected Garcinia species research  this network visualization. Cluster 1 (red) contains 12 authors, cluster 2 (green) has 11 authors grouped together, cluster 3 (blue) and 4 (yellow) has 7 authors linked together, while clusters 5 (purple) and 6 (teal) contains 6 authors respectively, cluster 7 (orange) has 5 authors linked together while 8 (brown) and 9 (pink) contains only 3 authors for both.

Co-citation
In total, the co-citation network of cited authors with a minimum of 150 citations has 83 authors meeting the threshold for co-citing authors. The total link strength of all authors is 211372. The 83 items have been classified into 4 clusters as presented in Fig. 5. In cluster 1 with 41 items grouped together (red), Iinuma has the greatest cocitation network with a total link strength of 17056 and 615 co-citations. In cluster 2 (green), 22 items are grouped together a researcher named Wang Y. has the highest total link strength with 6374 and 374 co-citations. In cluster 3 (blue), 13 items were grouped together, Bagchi D has the highest co-citation strength with a total link strength of 9539 and 402 co-citations. In cluster 4 (yellow), with 7 grouped items, Farombi has the highest TLS of 7733 with 776 co-citations.

Journal participation in selected Garcinia species research (1991-2021)
A total of 575 journals (sources) have published original research and conference papers on selected Garcinia species in the last thirty years. Table 4 presents their contribution in terms of total production, citation, average citation per publication and impact factor. Of the top 10 Journals, Acta Horticulturae is the most prolific journal used by researchers with 83 published articles although it also has the least citation score (TC: TP). Among the top 10 Journals in Garcinia species research based on the number of publications, the Journal of Agricultural and Food Chemistry has the highest citation score. The 3 most cited journals are the Journal of Agricultural and Food Chemistry, Journal of Ethnopharmacology and Food and Chemical Toxicology, with a TC: TP ratio of 89.75, 68 and 66.63 respectively. Also, these Journals have an impact factor greater than 4.
Bibliographic coupling of sources analysis provides thematic clusters that are based on those publications that share the same references (67). For bibliographic coupling, the relatedness of documents is relative to the number of references they share (68). Also, the size of the nodes (Journals) is proportional to the number of documents published in the journal, while the relative proximity of the nodes and the thickness of the links symbolize their degree of similarity based on the number of references they have in common (69). Fig. 6 shows the bibliographic coupling of Journals with at least 10 documents. Of the 1024 different journal sources that have been published on Garcinia, only 30 met the threshold and were classified into 3 clusters based on the relatedness of subjects of interests. Cluster 1 (red) 12 journals, cluster 2 (green) 12 journals and cluster 3 (blue) 6 items as shown in Fig. 6 (also presented in

Co-occurrence of author keywords in selected Garcinia species research (1991-2021)
Co-occurrence of keyword analysis is a powerful tool used to identify, describe and visually present the interactions between keywords in a scientific field (Table 6) (70,71). This tool analyzes the frequency of co-occurrence of 2 keywords i.e., it quantifies the number of articles in which these words appear together. The network visualization of Garcinia species research was carried out and of the 18744 keywords relating to this subject, 154 met the threshold of 50 sets. The keywords used most commonly also gives direction on where research on this subject is currently gaining ground. For instance, the top 10 keywords in Table  6 show the most frequently used keywords in Garcinia studies indicating that it is mostly used for its ethnopharmacological importance and as a possible natural remedy for illnesses.

Conclusion
Garcinia species have shown potential to improve a variety of illnesses, including hyperlipidemia, COVID-19, diabetes mellitus and neurodegenerative disorders and have been reported to be safe for consumption. The 3 species understudied (G. indica, G. cambogia, G. kola and G. mangostana) all have significant impact in the health industry because of the potentials in them to manage different varieties of diseases. Research undertakings have also demonstrated the potential industrial uses of the herbs in the health, pharmaceutical industries, clothing and petroleum industries and these may dominate the research emphasis in the immediate future, however, in terms of isolation of beneficial compounds more studies will be needed to maximize the benefits of these species.