Bioactive Components of Magical Velvet Beans

The plant Mucuna is an annual climbing shrub with long vines that can reach over fifteen meters in length. About 100–150 Mucuna species are found in the tropic and subtropic regions of both hemispheres of the earth. The genus Mucuna belongs to the family Leguminosae. It is commonly known as Kewanch, velvet bean, cowhage and kappikachhu and is found widely in India as a hardy, herba-ceous, vigorous, twining annual plant. The size and dimension of the Mucuna seeds, pods, platelets and leaves change from species to species. The hair present on pods is anthelmintic, which causes itching. People are seeking great attention towards Mucuna due to its several medicinal properties, including L-DOPA (L-3, 4-dihydroxyphenylalanine) along with supplementary antioxidants that are used for treating Parkinson’s disease and many neurodegenerative diseases. Thus it is being used in about 200 medicinal formulations. The current chapter outlines the work that determines the influence of different nutritional, anti-nutritional and medicinal values and bioactive agents from different parts of the Mucuna species present in India and its importance in medicine.


Introduction
Mucuna is a valuable genus of Leguminosae family; it has tremendous value in food and medicine. The genus Mucuna originated in Eastern India and China and then was transferred throughout tropical and subtropical regions of the world creating new populations [1]. Traditionally, Mucuna is known by different names including beans, buffalo beans, dopa bean, cowitch, kappikachhu and atmagupta. Out of 100 Mucuna species found worldwide, 8 species and 3 varieties of Mucuna are predominantly found in different localities of India [1,[2][3][4]. The Mucuna plant is an annual perennial climbing shrub with long vines having a length of 15-25 m with trifoliate leaves and yielding long inflorescences with purple or pale yellow flowers. They produce green or brown pods covered with rigid hair, which causes intense itching [5]. Pods contain four to six ellipsoidal-shaped seeds that are rich dark brown or blotched [6] varying from species to species. Mucuna seeds are a rich source of nutritional, antinutritional and phytochemical compounds containing l-dopa as a prime constituent [7]. The content of l-dopa varies between from species to species and locality to locality. Among them, M. pruriens is the most exploited species as a remedy against Parkinson's disease [8]. Due to huge Seeds of Mucuna are commonly used part of the plant, which are a rich source of nutritional and anti-nutritional compounds like l-dopa (anti-Parkinson's activity), antioxidants, phenolic, flavonoids, tannin, carbohydrates, starch, protein, micronutrients Sopanines and many more [9,12,26]. Antioxidant activities in this plant are mainly due to phenolic and various bioactive compounds present in the seed material [36,37]. There are various extraction techniques, different solvents and processing methods that were used to extract the biologically active compounds from the seed of Mucuna [26,31]. The prior study reports that M. macrocarpa, M. sanjappae and M. atropurpurea disclosed a higher level of l-dopa content, which also concludes that l-dopa content has a positive correlation to the protein content of seeds [12]. These high-yielding varieties of Mucuna can be commercially cultivated, which can thus serve to be a good option to lower the burden exerted on commonly used M. prurience variety [28]. LCMS analysis of four different species demonstrates the presence of diverse group of phenolics, alkaloids, flavonoids, different derivatives of gallic acid, l-dopa, catechin, alkaloids, quercetin, tannic acid, glycosides, saponins, tubastatin and a variety of amino acids in the seed extract [38]. Apart from that, it is also concluded that few anticancer compounds like Spergualin, sanggenon G, isopentenyl adenosine and spisulosine are also present in the seed extract [28,38].

Bioactive compounds from leaves and roots of Mucuna
The root extract of Mucuna has various activities like stimulant, thermogenic, purgative, emollient, diuretic anthelmintic, emmenagogue and tonic; hence, they are used in the vitiated circumstances in Veda and Ayurveda [39]. l-Dopa content of leaves and roots is as much as 1% and 4-7% in Mucuna plant [40]. Mucuna plants release secondary chemical compounds called allelochemical in the form of l-3,4-dihydroxyphenylalanine (l-dopa) in the surrounding environment which show an impact on growth of nearby plants, either negatively or positively. These substances are produced through its roots, seeds or leaves [41]. These secondary chemical agents play a role in damaging root growth, terminating seedling growth, inhibiting plantlet growth or suppressing seed germination of other plants [42]. Plant-box bioassay explains that the secondary chemical compound produced from the root of Mucuna is l-dopa [40], which affects the cell and root of various plant seedlings [41]. Leaf extracts are used to treat various complications like Anticataleptic, antiepileptic, aphrodisiac, antimicrobial, tonic and ulcers are some applications in which Mucuna leaves were reported being used previously [8,20,43,44].

Bioactive compounds from callus of Mucuna
Production of callus from Mucuna plant material is a new era in the advancement of biochemical engineering and industrial biotechnology, which has the potential to produce different biologically active agents from the explant [45,46]. Their application in cost-effective industrially important product formation is helpful for humankind, which upshots effective drug formulations and upsurges the nutritional level of food [47,48]. l-Dopa is a major component in different parts of Mucuna species [9]. This also helps in storing germplasm of endangered species, which in turn leads to regenerate new plantlets at any time. Production of callus from Mucuna species was done previously by the researcher at the lab scale [49]. An earlier study by Chattopadhyay et al. depicted the formation of callus culture of commonly used Mucuna pruriens [50]. Media containing various concentrations of media components affects biologically active chemicals and growth of the callus [51,52]. The use of different elicitors and precursors are studied by Nandeo and Patel et al. [53,54]. Implementation of precursor in the media of callus enhances the phenolic content as reported in prior studies. The percentage of phenolic is greater in callus culture than in seeds, which is very helpful for industrial production [55,56].

Bioactive compounds from cell suspension of Mucuna
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are stress-producing free radicals, but at usual level perform an important part in the physiology of the body [57] to accommodate the massive demands for l-dopa and other secondary metabolites. In vitro production of biologically active compounds from suspension culture is predominantly studied before in Mucuna plant by Chattopadhyay et al.
[50]. The use of mevalonic acid and its precursor gibberellic acid affect the growth. l-Dopa in callus exhibits a declining trend in fresh weight with a rise in concentration of l-dopa as shown by Desai et al. [52]. The comparative study of production of l-dopa from cell suspension culture and effect of elicitor on two different species like Mucuna pruriens L. and Mucuna prurita H were also done previously [58]. Largescale production of phytochemicals and l-dopa was done from Mucuna pruriens L. Commercial production of the drugs (l-dopa), phenolic flavonoids and antioxidants using cell suspension cultures is in extensive practice nowadays.

Antioxidant activity of Mucuna species
Numerous studies on antioxidant activity and phytoconstituents content of Mucuna seeds, leaves and roots were performed previously [4,7,19,30,31,[59][60][61][62]. Optimization of different solvents for the extraction of antioxidants was done by Aware and Patil et al. [9,10,26]. They concluded that depending on solubility of antioxidant compounds present in different species of Mucuna, concentration of antioxidants differs. Most commonly, ethanolic extract of Mucuna shows good antioxidant activity due to high phenolic content [43]. Some reports also conclude that water is a universal solvent, which shows significant quantity of phenolic, flavonoids and strong antioxidants that can scavenge free radicals using different assays. Diseases like neurodegenerative diseases, cardiovascular diseases, aging, cancer, rheumatoid arthritis and inflammation are caused by oxidative stresses, which are protected by ROS and RNS [60]. LCMS report of four different species of Mucuna determines the presence of various components like phenolic, flavonoids and bioactive compounds, which are responsible for production of reactive species [38].

Antimicrobial activity of Mucuna species
There are several compounds in Mucuna that contribute for the antimicrobial activity as reported in a previous study [38,43]. These compounds are responsible for the treatment of various infectious diseases and ulcers [63] of study was done by Pujari et al., who concluded that methanol extract of seeds of Mucuna pruriens was found to impart the best inhibiting activity among all scrutinized pathogens as compared to ethanol and acetone solvents. But alcoholic extract of Mucuna pruriens (L.) leaves has significant antioxidant and antibacterial activity, which has strongly recommended the use of Mucuna leaves and seed extract in traditional as well as modern medicine [65].

Protective effect against snake venom
Snakebite kills countless people annually since ancient days [66]. Various reports show the cross-reactivity between the enzyme of snake venom and protein from Mucuna, which determines the activity of Mucuna against snake venom [32,[67][68][69]. Betancur et al. in their review on therapeutics of antisnake venom explain the effectiveness of herbal plants, which act as coadjuvants and thus help to nullify the venom toxic action [68]. In recent literature, Kasturiratne et al. studied the global scenario of snakebite and deaths. They also elucidate that various traditional medicines were sometimes preferred with western drugs [70]. The protective effect of Mucuna in a study on mice or rat models proves that it has a good activity for curing snake bite, than few reported antivenom [71,72].

Anti-Parkinson's activity of Mucuna species
Parkinson's disease (PD) was initially discovered by Dr. James Parkinson in 1817. It is a chronic neurological disorder triggered by a progressive loss of dopaminergic neurons present in the nigrostriatal part of the brain and found to be common in the US [73]. The major signs of the disease are complications in body movements, speaking, walking and many more complications arise as the disease progresses. Anti-Parkinson's potential of Mucuna is well known from ancient times due to its l-dopa content [7,74]. l-Dopa is a precursor of dopamine used in the treatment of neurodegenerative disorders. Various scientists studied the potential of Mucuna to produce l-dopa as a source of anti-Parkinson's drug [8,19,75]. l-Dopa with other phytochemical compounds has a cumulative effect on the management of Parkinson's disease. Patil et al. describe that there is a correlation among the l-dopa, protein and carbohydrate content [12]. Mucuna is a rich source of antioxidant compounds, which performs a very important role in the physiology of the body mainly functioning in the inhibition of damage occurred because of free radicals [76]. There are hundreds of compounds that function as antioxidants in the plant system mainly vitamins, polyphenols, enzymes, flavonoids and metals like zinc, selenium, etc. [77]. The efficiency of the use of l-dopa and another dopaminergic agent in the treatment of Parkinson's disease is reviewed previously by Koller and Rueda [78]. The use of plants for the treatment is more beneficial than chemically manufactured medicines due to their infinitesimal occurrence of secondary complications by routine use and economical feasibility.

Use of Mucuna species in soil fertility
Cover crops have a role in the nitrogen-fixing bacteria and improvement of soil fertility by restoration of soil nutrients. Enormous use of chemical fertilizer and water in soil makes soil infertile, to overcome this problem, farmers are implementing traditional methods to enhance soil fertility. Mucuna is one of the best examples of a cover crop that has a rich source of biological natural products, which will increase the enhance soil fertility and fix atmospheric nitrogen [35].

Conclusion
Mucuna is a medicinally and biochemically valuable plant used from ancient days, having a large market value due to the presence of a large number of bioactive compounds. The content of phytochemical compounds and other bioactive agents present in Mucuna fluctuates from species to species. l-Dopa is a chiefly present amino acid found abundantly in Mucuna plant, which is used for the treatment of Parkinson's disease. It also contains a great amount of phenolics, flavonoids and antioxidants, which play a role in releasing oxidative stress. It also acts as a protein-rich diet. Due to all these properties, Mucuna has several applications in the pharmaceutical and food industries thereby uplifting the demand of Mucuna in day to day life.