Phytochemical and pharmacological properties of Curcuma aromatica Salisb (wild turmeric)

Curcuma aromatica Salisb. (C. aromatica) is commonly known as wild turmeric. Curcuma aromatica is an essential herbal plant and it has been extensively used in traditional medicine for centuries. It has been used for the treatment of gastrointestinal ailments, arthritic pain, inflammatory conditions, wounds, skin infections, and insect bites. This article aims to review the phytochemical and pharmacological aspects of C. aromatica and to provide a guide and insight for further studies. Electronic repositories, including Web of Science, Google Scholar, ProQuest, Science Direct, Scopus, and PubMed, were searched until December 2019 to identify studies relating to C. aromatica. A systematic analysis of the literature on pharmacognostical, physicochemical, and nutritional contents, bioactive compounds, and biological activities of C. aromatica was carried out, and ideas for future studies were also coined. A total of 157 articles concerning in vitro or in vivo (or both) researches on C. aromatica have been evaluated. Analyses of the data showed that C. aromatica consists of various classes of compounds, including alkaloids, flavonoids, curcuminoids, tannins, and terpenoids, that formed the bases of its pharmacological activities. The reviewed data also revealed that C. aromatica possessed the pharmacological effect of anticancer, antidiabetic, antioxidant, anti-inflammatory, antimicrobial, antitussive, antiepileptic, analgesic, wound healing, and insect repellent activities. This review has systematically compiled and summarized the literature related to the nutritional values and bioactive compounds, as well as the biological activities of C. aromatica. To the best of our knowledge, this is the most comprehensive review reported on C. aromatica.


INTRODUCTION
Curcuma aromatica Salisb. (C. aromatica) is known as "vanaharidra" in Ayurveda, wild turmeric in English, "jangli haldi" in Hindi, and "Yu Jin" in Chinese. It is commonly used as a coloring and flavoring agent, as well as in many traditional medicines in Southeast Asian countries (Kanase and Khan, 2018). Therapeutically, it possesses a strong antimicrobial effect and has been used since ancient times as a remedy against various microbial infections (Ahmed et al., 2008). The rhizomes of C. aromatica are used in traditional medicine for eliminating blood stasis, delaying the ageing process, pain relief, and protecting against liver diseases (Dosoky and Setzer, 2018). Also, the rhizomes of C. aromatica are used internally as a tonic and carminative, while being topically applied for various skin ailments, sprains, bruises, as an antidote for snake venom, and also to enhance complexion (Ahmad et al., 2011;Dosoky and Setzer, 2018;Preethi et al., 2010;Xiang et al., 2017). Villagers in the northeastern part of India are using aqueous extracts and paste (with milk) of C. aromatica rhizomes and leaves for the treatment of indigestion, rheumatism, wound healing, and dysentery and also in the prevention of helminth infections (Sikha et al., 2015). In Thailand, the rhizome and roots of C. aromatica are often used in cosmetics and spas for skincare (Choochote et al., 2005). The traditional uses of C. aromatica rhizome extract as medicine are now being explored in modern scientific research for the possible development of modern medicine including but not limited to antimicrobial, antioxidant, anti-inflammatory, anticancer, antidiabetic, antiangiogenic, antitussive, antiobesity, antiacne, antiallergic, and wound healing (Pant et al., 2013;Preethi et al., 2010;Revathi and Malathy, 2013).
The rhizome of C. aromatica has been reported to be rich in medically essential phytochemicals, such as alkaloids, flavonoids, curcuminoids, tannins, and terpenoids (Anoop, 2015;Kanase and Khan, 2018). As this plant has considerable therapeutic potential, the extraction and characterization of the essential bioactive compounds with vital medicinal properties may provide opportunities relating to pharmaceutical applications. Therefore, in this review, we have compiled and critically analyzed the reported studies on the phytochemical and pharmacological properties of C. aromatica rhizomes, leaves, and its essential oil. We hope this will provide future insight into the medical application of C. aromatica for the treatment of various diseases.

Botanical description
Curcuma aromatica, commonly known as wild turmeric, belongs to family Zingiberaceae and genus Curcuma. The genus Curcuma consists of 70-100 species that are generally rhizomatous herbs and are well known for their therapeutic potential (Ahmed et al., 2008). The most commonly found species are Curcuma longa Linn., C. aromatica Salisb., Curcuma amada Roxb., Curcuma angustifolia Roxb., Curcuma caesia Roxb., and Curcuma zedoaria Rosc. found in various regions of the world (Sikha et al., 2015). C. aromatica is only second to C. longa (turmeric) as the crucial species of the family (Ahmed et al., 2008;Shivalingu et al., 2016). C. aromatica is widely distributed in tropical and subtropical regions and mostly cultivated for its rhizomes mainly in India, China, and Japan (Ahmed et al., 2008;Sikha et al., 2015). Curcuma aromatica is an annual, erect herb with a characteristic light yellow aromatic rhizome and camphoraceous smell (Anoop, 2015). The plant develops clumps of erect, unbranched leaf stems that on full growth can reach a height of about 1 m from the stout, underground rhizome and with enlarged colored bracts tipped with pink. The inflorescences usually appear from the base of the rhizomes (Fig. 1A) before the leaves are produced in early spring. The flowers are fragrant and pinkish-white with an orange lip. The plant grows fast, wild, and vigorously in the monsoon season. The foliage dries in late autumn and the rhizomes remain dormant in winter; the rhizome ( Fig. 1B), when mature, possesses a characteristic fragrance (Schultes, 1991).

Nutritional and physiochemical contents
Rhizomes are the main edible portions of C. aromatica. They are well known for their high nutritional value and are particularly rich sources of carbohydrates, proteins, alkaloids, flavonoids, vitamin C, beta-carotene, polyphenol, fatty acid, and essential oils (Ravindran et al., 2007). The rhizomes of C. aromatica are mainly used as a spice and food flavoring, as well as a coloring agent in food preparation due to their pleasant aroma and taste (Rajkumari and Sanatombi, 2018). The nutritional compositions of the rhizomes are crude protein (19.44%), lipid (2.5%), and carbohydrate (97.5%). The rhizomes also have a moisture content of 19% and an ash content of 3.21% (Jain and Parihar, 2017). Other physicochemical parameters reported elsewhere were ash content (16.6% total ash, 2.8% acid insoluble ash, and 3.93% water-soluble ash), extractive values (0.4% alcohol soluble extractive value and 0.8% water-soluble extractive value), and moisture content (3.14%) (Jain et al., 2016).
The total phenolic content of the rhizome extracts of C. aromatica is reported in the range of 151.33 ± 13.9 μg/mg eq to gallic acid (Jain and Parihar, 2017) to 265 ± 1.08 mg/g of ascorbic acid (Srividya et al., 2012), and the total flavonoids content ranges from 106.8 ± 2.76 μg/mg eq to quercetin (Jain and Parihar, 2017) to 175 ± 1.56 mg/g of rutin (Srividya et al., 2012).
Thus, the presence of the above-mentioned phytochemicals shows the protective and disease preventive nature of the plant. It is also noteworthy to mention that there are not many phytochemical studies on the leaves of C. aromatica compared to other Curcuma species (i.e., C. caesia, C. longa, C. amada, and Curcuma xanthorrhiza) (Neha et al., 2013;Saxena and Sahu, 2012;Seema and Kaur, 2016).

Bioactive compounds
The bioactive compounds isolated and identified from the extracts and essential oils of C. aromatica obtained from different extraction methods are tabulated in Table 1 and 2, respectively. The chemical structures of some of the main bioactive compounds are shown in Figure 2. From the last three decades (1987-2019), a total of 79 major compounds have been identified from the leaves, rhizomes, and essential oils of C. aromatica. Most of the major compounds belong to alkaloids, flavonoids, curcuminoids, tannins, and terpenoids. Interestingly, there is no significant difference between the compounds found in the extracts of the leaves and rhizomes or their essential oils of C. aromatica grown either in the same or in different regions. A total of 37 ( Table 1) compounds have been isolated and identified in the solvents extracts of leaves and rhizomes of C. aromatica. An additional 42 compounds were isolated and identified in the essential oils from the leaves and rhizomes ( Table 2). The essential oils were also reported to have more potent antimicrobial, antioxidant, anticancer, and anti-inflammatory activities than the solvent extract counterparts (Xiang et al., 2018).

Pharmacological activities of C. aromatica
Various studies have been reported on the pharmacological activities of C. aromatica as summarized below and in Table 3.

Anticancer activity
Cancer is a disease characterized by an uncontrollable growth of cells in the human body, forming tumors of malignant cells (Greenwell and Rahman, 2015). Cancer is a major public health problem and the second leading cause of death in both developed and developing countries (Moraes et al., 2017). The current regimen, including surgery, chemotherapy, and radiotherapy, is often expensive and associated with severe side effects (Greenwell and Rahman, 2015). Hence, the focus has shifted to identifying new, safe, and cost-effective alternative treatment against cancer, preferably from natural sources. Bioactive compounds, including 1,8-cineole, ar-curcumene, ar-turmerone, β-elemene, camphor, curcumol, curdione, germacrone, linalool, xanthorrhizol, and zingiberene, from the essential oil of C. aromatica have been proven to possess anticancer properties.
Xiang et al. (2018) studied cytotoxic activities of essential oils extracted from the rhizomes of C. aromatica by colorimetric MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5diphenyltetrazolium bromide] assay against prostate cancer cells line [lymph node carcinoma of the prostate (LNCaP)] and human hepatoma cells line (HepG2). The essential oils showed significantly higher anticancer activity against LNCaP (IC 50 of 1.14 ± 0.02 µg/ml) than the HepG2 (IC 50 of 168.94 ± 1.93 µg/ ml). In another study, the infusion of essential oils via the hepatic artery exhibited rapid therapeutic effects in patients with primary liver cancer and transplanted hepatoma rat model, respectively (Cheng et al., 1999). The essential oils were also reported to have a protective effect against intestinal metaplasia and esophagoduodenal anastomosis in a rat model (Li et al., 2009). On the other hand, Hou et al. (2011) investigated the inhibitory effect of curdione isolated from the rhizome of C. aromatica on CYP3A4 using 1α,25-(OH)(2)-D(3)-treated Caco-2 clone cells. The results revealed that curdione showed the best inhibitory activity with IC 50 of 3.9 μg/ml after 72 hours of treatment with no cytotoxic effect. Hence, it was concluded that the inhibitory activity of curdione accelerates the degradation of CYP3A4. The molecular mechanisms of apoptotic activity of curcumin Table 1. Major compounds isolated from solvent extracts of leaves and rhizomes of C. aromatica.

Antidiabetic activity
Diabetes mellitus is a chronic, life-threatening systemic disease leading to multiple complications, such as blindness, kidney failure, amputations, strokes, and heart attacks (Meral et al., 2001). Diabetes mellitus causes oxidative destruction of cellular membranes and redox imbalance (within the cells) called oxidative stress (Cheeseman, 1993), which leads to an increased production of free radicals and a decreased antioxidant defense mechanism in the body. Hence, it has been hypothesized that, in diabetes mellitus, free radical production increases due to the increased oxidative stress and decreased antioxidant production (Ahmad et al., 2014;Meral et al., 2001). Thus, the increased production of free radicals could be considered as one of the significant complications of diabetes mellitus (Meral et al., 2001). Curcuma aromatica possesses compounds such as 1,8-cineole (Miri, 2018;Saito et al., 2004), ar-turmerone (Lekshmi et al., 2012), curcumin (Chuengsamarn et al., 2012;Roxo et al., 2019;Widowati et al., 2018), curcumol (Raafat and Omar, 2016), demethoxycurcumin (Jayaprakasha et al., 2006), germacrone (Hamdi et al., 2015;Hossain et al., 2015;Makabe et al., 2006), and xanthorrhizol (Kim et al., 2014) that have been well reported to have antioxidant and antidiabetic properties. Besides, Srividya et al. (2012) reported that the toluene extract of rhizomes of C. aromatica significantly decreased the glucose level from 278.53 to 116.5 mg/dl, increased protein level from 3.09 to 5.78 mg/dl, decreased cholesterol level from 292.33 to 134.50 mg/dl, and reduced the triglyceride level from 85.66 to 64.16 mg/dl upon oral administration at a maximum single dose of 400 mg/kg in streptozotocin-induced diabetic rats.

Antioxidant activity
An antioxidant is a molecule that scavenges and neutralizes free radicals by donating an electron, thus reducing the damaging power of free radicals (Halliwell, 1995). Methanol and aqueous extracts of C. aromatica rhizomes have been proven to have comparable potency to L-ascorbic acid, a well-known antioxidant with IC 50 less than 60 µg/ml. In another study, Xiang et al. (2017) studied the antioxidative activity of the essential oils of C. aromatica rhizomes from 12 different locations in China using the 2,2diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay. The results again proved the antioxidative potency of C. aromatica with IC 50 ranging from 1.57 to 21.36 µg/ml, which was indeed better than the control, Trolox C (IC 50 8.82 µg/ml).

Antimicrobial activity
Microbial contamination and resistance are a few of the significant challenges in the food, beverage, and pharmaceutical industries. For instance, antimicrobial agents, including food preservatives, have been used to inhibit the growth of food-borne bacteria and prolong the shelf life of processed foods (Rahimi-Nasrabadi et al., 2013). Many plant derivatives, including those of C. aromatica, have been shown to possess antimicrobial properties.
A study conducted by Revathi and Malathy (2013) revealed that crude hexane extract of C. aromatica was effective against Gram-positive bacteria and ineffective against the tested Gram-negative bacteria. The phytochemical analysis identified that the antimicrobial activity was attributed to germacrone. Antiulcer Ko and Leung (2010) Insect repellent Eigenbrode and Trumble (2019) It should be noted that germacrone has also been reported to possess other biological activities, including anti-inflammatory, antitussive, antitumor, and antifungal properties . On the other hand, the essential oil extracted from the fresh rhizomes of C. aromatica has been shown to inhibit the growth of both Gram-positive and Gram-negative bacteria (Ahmed et al., 2008). Curcumin (diferuloylmethane) was then isolated and found to be active against Staphylococcus aureus strains and Saccharomyces cerevisiae. In another study, the essential oil of C. aromatica was also reported to have higher antifungal activity against S. cerevisiae (183.18 μg/ml) than the essential oils from other Curcuma species, including Curcuma nankunshanensis, Curcuma elata, Curcuma kwangsiensis var. nanlingensis, Curcuma yunnanensis, Curcuma rubescens, and Curcuma sichuanensis (Xiang et al., 2018). Apart from germacrone and curcumin, C. aromatica is also composed of other bioactive compounds, such as ar-turmerone (Dhingra et al., 2007;Lee, 2006), camphor (Kordali et al., 2005Kotan et al., 2008;Viljoen et al., 2003;Zafar et al., 2019), curdione (Naz et al., 2010), linalool (Queiroga et al., 2007;Van Zyl et al., 2006), and xanthorrhizol (Hwang et al., 2000;Rukayadi and Hwang, 2007;Rukayadi et al., 2006), that are reported elsewhere to have an antimicrobial effect against both fungi (Aspergillus flavus, Fusarium semitectum, Colletotrichum gloeosporioides, Colletotrichum musae, Candida albicans, Candida glabrata, Candida guilliermondii, Candida krusei, Candida parapsilosis, and Candida tropicalis) and bacteria (Escherichia coli, S. aureus, and Bacillus cereus). Perhaps these findings are not surprising, as C. aromatica often is one of the ideal plant sources for the treatment of various infectious diseases in the conventional and Ayurvedic regime.

Anti-inflammatory activity
Inflammation has been described as a transitory biological tissue response to dangerous stimuli, for example, wounds, exogenic, and endogenic antigens, meant to clear or remove the stimulus and repair the wounded tissue that ultimately leads to tissue regeneration and normal homeostasis (Egger, 2012). Even though inflammation is an affirmative body defense mechanism, dysregulated and chronic inflammatory reactions have been well documented as underlying causes of many systemic diseases, including diabetes, asthma, atherosclerosis, obesity, cancer, and pain, thus contributing to the increased cost of healthcare to the society (Mizuno et al., 2011).
However, an undeniable fact is that most of the conventional nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, and immunosuppressant drugs used to treat all kinds of inflammatory conditions are linked with unfavorable side effects, such as headache, ulceration, gastric irritation, perforation, hemolytic anemia, hyperglycemia, and many more (Bagad et al., 2013). Considering these drawbacks associated with these drugs, an alternative source especially from medicinal plants that are usually considered safe is incessantly being investigated for probable anti-inflammatory activity.
Xiang et al. (2017) studied the anti-inflammatory activity of the essential oils of C. aromatica rhizomes obtained from 12 different locations in China. In their study, ear edema was induced by 12-O-tetradecanolphorbol-13-acetate in mice. Different groups of mice received different essential oil treatments, and ibuprofen was used as a positive control. Generally, all the essential oils showed anti-inflammatory activity on a dose-dependent fashion from 20.56 to 61.34% and surprisingly superior to ibuprofen (17.84%-54.57%), which is known for its anti-inflammatory effect. The histological and immunohistochemical analysis further showed tissue relief from inflammation after treatment with both essential oils. Cytokine analysis showed a significant decrease in the expression of COX-2 and TNF-α in the essential oil-treated groups compared to the untreated group. However, the difference was not significant compared to the ibuprofen-treated group. The extracts of C. aromatica rhizomes were also reported to have a promising anti-inflammatory effect similar to prednisolone when tested on the inflamed paw of mice induced by carrageenan (Ahmed et al., 2008).

Antitussive activity
One study has reported on the antitussive activity of C. aromatica. Marina et al. (2008) revealed that the ethanol extract of the plant possessed a promising and comparable antitussive effect with codeine phosphate in a dose-dependent fashion. The extract inhibited 79% of cough at a concentration of 400 mg/kg body weight after 1.5 hours of oral administration, which is similar to codeine phosphate (87% at a concentration of 40 mg) in mice. The acute oral toxicity study of the ethanol extract showed no adverse effect up to the maximum dose of 4 g/kg.

Analgesic activity
The use of analgesic drugs, such as opiates and NSAIDs, for pain relief has been stagnated as these drugs are reported to have adverse side effects, including addiction and gastrointestinal disorders (Khokra et al., 2012;Maniyar and Sriraj, 2017). In an effort to find natural alternatives to these drugs, several plants, including C. aromatica, have been studied and have showed potent analgesic activity. Pranav  studied the analgesic effect of aqueous extract of C. aromatica rhizomes by Eddy's hot plate (55°C) method in rats to induce pain due to heat. The extract was administered orally at a concentration of 300 and 500 µg/kg and showed prolonged pain latency compared to the diclofenac sodium (10 mg/kg). In another study, a reduced number of writhes by mice were observed in the acetic acid-induced writhing test after the administration of aqueous extract of the rhizomes of C. aromatica (Huang et al., 2007). The analgesic activity of C. aromatica was attributed to the presence of 1,8-cineole (Takaishi et al., 2012;Zheng et al., 2019), linalool (Souto-Maior et al., 2017), borneol (Xiong et al., 2013, camphene (Quintans-Júnior et al., 2013), and camphor (Adams, 2012). Govindarajan et al. (2004) and Mukherjee et al. (2000) studied the wound healing properties of the powdered rhizomes of C. aromatica incorporated in an ointment of soft white paraffin. The ointment was topically applied to acute wounds on rabbits and resulted in significant wound contraction and complete epithelization within 9-11 days. Similarly, cream formulations of C. aromatica rhizome extracts also showed significant wound healing properties when applied externally on excision wounds of Swiss albino mice (Kumar et al., 2009).

Antiepileptic activity
Nonetheless, the plant also consists of compounds that possess antiepileptic effect which is including androstan-17-one (Kaminski et al., 2005) and linalool (Bahr et al., 2019;Souto-Maior et al., 2017), but the activity is yet to be evaluated using C. aromatica extracts or essential oils.

Insect repellent activity
Apart from pharmacological use, C. aromatica is also extensively studied as a potential insecticide. Lack of sufficient knowledge on plant-based oviposition deterrents lead to the current overuse of synthetic insecticides and insect growth regulators to monitor larval instars of mosquitoes, which are believed to cause resistance to insecticides, environmental contamination, and threats to humans and other species, thus representing significant limitations to their successful employment (Benelli, 2015). Recently, the use of some plantderived products, such as essential oils, has shown to provide safer and effective alternatives to synthetic pesticides and repellents (Alshebly et al., 2017).
A study conducted by Singh et al. (2002) showed that the essential oil of C. aromatica possesses a better insecticidal effect against Odontotermes obesus Rhamb. (a pest of sugarcane) than the commercial synthetic insecticides, Thidon and Primoban-20. At a dose of 3 µl and 6 µl, the essential oils of C. aromatica showed a percentage mortality rate of 50% and 100%, respectively, after 2 hours of exposure, whereas Thidon showed a mortality rate of 10% and 20%, and Primoban-20 showed 10% and 30% under the same dose and exposure time, respectively.
Pitasawat et al. (2003) showed that the ethanol extract could provide repellence against Aedes togoi mosquito on human volunteers with ED 50 and ED 95 values of 0.061 and 1.55 mg/cm 2 , respectively. The biting protection lasted for 3.5 hours when the extract was applied topically at a concentration of 25% (w/w). Neither dermal irritation nor adverse effect was reported on the human volunteers. The ethanolic extract was further shown to provide a protective effect against other mosquito species, including Armigeres subalbatus, Culex quinquefasciatus, and Cx. tritaeniorhynchus under field conditions. Choochote et al. (2005) also investigated the antimosquito effects, including larvicidal, adulticidal, and repellent activities, of the hexane rhizome extracts and essential oil of C. aromatica against Aedes aegypti mosquitoes. The essential oil showed a significantly higher larvicidal activity (LC 50 of 36.30 ppm) against the 4th instar larvae of A. aegypti than that of the hexane extracts (LC 50 of 57.15 ppm). On the other hand, the adulticidal activity of the hexane extract was found to be slightly more effective (LC 50 of 1.60 μg/mg) against female A. aegypti than the essential oil (LC 50 of 2.86 μg/mg). However, these two products showed a significant repellent activity against female adult A. aegypti. The hexane extract showed higher repellent period (total protection time of 1 hour) when applied at a concentration of 25% than that of the essential oil (0.5 hours). The phytochemical analysis revealed the presence of xanthorrhizol, 1H-3a, 7-methanoazulene, curcumene, germacrone, and camphor as the major constituents, with the exception of germacrone and camphor that are present only in the essential oils.

CONCLUSION
This review spotlighted important findings of C. aromatica as one of the most medically crucial plant species of the genus Curcuma. The review also justifies the reason for the use of this plant in traditional medicines in India, China, and other Southeast Asian countries. However, scientific findings are still lacking on the in vivo toxicity, clinical trials, and nutritional content of this plant. These findings are crucial to providing immense opportunities for the development of new C. aromatica-based products in pharmaceutical industries and cosmetics.

RECOMMENDATIONS
It should be emphasized that the medicinal value of C. aromatica has not been scientifically and extensively studied as compared to C. longa, which is regular turmeric. This could be due to improper farming practices, habitat destruction, deforestation, and the high demand of the pharmaceutical industry for wild plant sources which make this plant one of the most endangered plant species in many South Asian countries, hence leading to the limited supply of the plant. If these hurdles can be mitigated satisfactorily, C. aromatica has the potential to be used for the treatment of various diseases. We believe that both conservation and sustainable use of this plant should not be underestimated. We recommend that conservation strategies, such as in situ and ex situ conservation strategies, should be adequately taken into consideration for the sustainable use and proper harvesting of this medicinal plant. Also, biotechnological approaches, such as micropropagation, molecular markerbased approaches, and tissue culture, are promising alternative approaches to produce high-value medicinal plants, including C. aromatica. These methods may shorten the breeding time of the plant.
Although C. aromatica has been extensively used in traditional medicine for the treatment of various ailments and scientifically studied for medicinal use, to our understanding, no commercial product is currently available in the market. This could be due to the safety concern on the systemic administration of C. aromatica. Hence, more safety studies are required to prove the medicinal value of C. aromatica. We strongly believe that these problems can be extenuated through systematic investigation of the whole plant, including toxicity and clinical studies for safety assessment.

ACKNOWLEDGMENT
This work was supported by the Short-Term Grant from Universiti Sains Malaysia (Grant no. 304.PFARMASI.6315110).