In order to meet the global healthcare needs, traditional medicine systems have played a very important role. Indian Systems of Medicine being one of the largest and oldest systems constitutes all the medicines which have their origin in India. Plants have played a very vital role in sustaining and improving quality of human life and have served humans well as important components of medicines, seasoning, beverages, cosmetics, and dyes. Due to this fact, the focus on plant research has increased all over the world. There are any herbs that are used to treat liver, cardiovascular, digestive, metabolic and central nervous system (CNS) disorders. Medicinal plants or herbal drugs and their extracts containing isolated compounds have showcased a wide spectrum of biological activities. One of such a plant with wide applications is C. esculenta .

Taro, a common name for the corms and tubers of numerous genera of the family Araceae, is a source of edible corms of C. esculenta. It is most extensively cultivated in Southeast Asia by several common names like Arbi, Arvi and Eddoe. The juice of the plant leaf is rubefacient, stimulant, styptic and is useful in internal haemorrhages, adenitis, otalgia and buboes. The corm juice is demulcent, laxative and anodyne. The leaves of the plant have been found to exhibit antihelminthic, anti-diabetic and anti-inflammatory activity [1]. Colocasia species is an ancient crop used all over the world; Africa, Asia, the West Indies, and South America. It is grown throughout the humid tropics. Its edible corms and leaves are traditionally used for liver related ailments [2]. Colocasia esculenta (L) Schott of the family Araceae is an herbaceous perennial plant. The crop is cultivated as annuals. The green leaves of the plant are large in size and are often described as ‘Elephant ear’. They can reach up to 1-2 m high during growth period. The main edible parts of the crop are the starchy, tuberous roots; however, the leaves of the plant are also used as a leafy vegetable. The leaves of C. esculenta have been reported to be rich in nutrients including minerals and vitamins such as phosphorours, calcium, vitamin C, iron, riboflavin, thiamine and niacin [3]. Among various edible plants from Araceae family commercially cultivated in India, C. esculenta has a significant dietary importance for having multiple uses in various culinary preparations of its edible parts i.e., corm, stem and leaves. C. esculenta fresh edible leaves are rich sources of protein, dietary fibre, ascorbic acid and some nutritionally important minerals. Leaf juice of the plant also finds its application in scorpion sting, in snake bite, in food poisoning from plant origin, etc. The plant also finds its application in Ayurveda identified ailments viz. vata and pitta, constipation, alopecia, stomatitis, haemorrhoids and general weakness [4,5]. Colocasia antiquorum is found to possess hepatoprotective activity against liver injury in rats that were experimentally induced [2]. C. esculenta is reported to possess hypoglycemic efficacy due to the presence of cyanoglucoside [6]. The plant is also reported to possess hypolipidemic and antihyperlipidemic activity due to the presence of arabinogalactan [7] and mono and digalactocyl diacylglycerols. The plant gets its antifungal property due to presence of cystatin [8]. Antibacterial activity of C. esculenta has been reported by Ravikumar et al. [9].

The objective of this review article was to shed light on the vast applications of traditionally used herb, Colocasia esculenta. This contribution also provides a broad review of botanical features, chemical constituents, pharmacological profile and medicinal/ pharmaceutical applications of C. esculenta.

Colocasia esculenta Linn. (Figure 1) is a tall herb having tuberous or a stout short caudex, leafing and flowering together. Leaves are simple and have a stout petiole, ovate-cordate or sagittate-cordate, lamina peltate. Spadix is shorter than the petiole and much it is shorter than the spathe rather than slender. Appendix much shorter than the inflorescence, style very short; stigma discoid [10]. It is erect, elongateconical or fusiform, subulate or abbreviate. Erect petiole is up to 1.2 m in length, with a dull and non-polished surface above, coloured or paler beneath. They are rarely glaucous. The leaf peduncle is shorter than the petiole. Spathe is pale yellow and measures 15 to 35 cm in length; tube greenish, oblong. The lamina is narrowly lanceolate, convolute, acuminate and curved slightly backwards in flower. Female inflorescence is short but male inflorescence is long, cylindrical and usually interposed neuters between the two. Seeds oblong, sulcate. Albumen copious; embryo axile. The plant stem is above ground and swollen slightly at the base of the leaf-sheaths, arising from a hardtapering rhizome; stolon’s and a tuberous rhizome suckers are sometimes present.

Figure 1: Picture of parts of Colocasia esculenta plant.

Leaf microscopy

Histological features of C. esculenta leaf are summarised below [11].

Epidermis: Single layer of spherical to polygonal cells with cutinized upper surface are present in upper epidermis of the leaf. The shape of the cells are straight to slightly beaded anticlinal walls and wavy with presence of Chlorophyll in epidermal cells. Lower epidermis shows single layer of polygonal cells which have straight to slightly beaded anticlinal walls. The lower epidermis also shows presence of papillae and paracytic type of stomata.

Mesophyll: Mesophyll shows dorsiventral arrangement, differentiated into palisade and spongy parenchyma. Chlorophyll and phenolic compounds are present in palisade cells.

Spongy parenchyma: The leaf shows presence of vacuoles and is made up of parenchymatous cells which varies in sizes and shapes measuring about 7-9 cells in thickness. Interspersed vascular elements are present intermittently. A majority of cells are filled with compound-type starch grains which are simple, spherical with centric helium and less prominent striations.

Conducting tissue system: Layer of parenchymatous bundle. The larger vascular bundles are surrounded by sclerenchymatous bundle sheath which extends up to the upper or lower or both epidermis [11]. The vascular bundles present are simple and each one of them are surrounded by a single.

Flavonoids and triterpenoids are the two pharmacologically active groups of compounds mainly present in the Colocasia leaf extracts. The flavanoids that are present in the Colocasia leaf extracts are vicenin-2, iso-vitexin, iso-vitexin 3’-O-glucoside, vitexin X’’-Oglucoside, iso-orientin, orientin, orientin7-O-glucoside, leteolin 7-Oglucoside [12]. The leaves of the plant also contains fibres, calcium oxalate, minerals (Calcium phosphorus etc.), and starch, Vitamin A, B, C, etc. [13]. Phytochemical investigations on the Colocasia extracts have shown the presence of anthocyanins viz. cyanidin-3-rhamnoside, cyanidin-3-glucoside and pelargonidin-3-glucoside. These anthocyanins have antioxidant activities as evident from previous studies [14-16]. It is due to these anthocyanins that the C. esculenta plant leaves showcases hepatoprotective as well as anti-lipid peroxidative activity. The tubers of C. esculenta contains globulins that accounts for around 80% of the total tuber proteins present. The starch content present in the flour varies from 73-76% and the starch yields are in the range of 51-58% [17]. The starch contains 0.23-0.52% lipid and 0.017-0.025% phosphorus in the form of phosphate monoester derivatives [17]. The nitrogen content of the flours varies from 0.33-1.35%. Table 1 shows chemical constituents of different parts of C. esculenta plant.

Table 1: Chemical constituents of different parts of Colocasia esculenta plant [12,13,17-21].

Antimicrobial activity

The aqueous extract of C. esculenta has been reported to possess antimicrobial activity. Study was performed for isolates of bacteria namely Escherichia coli , Aeromonas hydrophila , Flavobacterium sp ., Edwardsiella tarda , Klebsiella sp., Salmonella sp., Vibrio alginolyticus , V. parahaemolyticus , V. cholerae and Pseudomonas aeruginosa . The plant extract showed maximum activity against S. mutans amongst all the selected strains of microbe. The extract of C. esculenta exhibited good antimicrobial activity against some of bacteria and fungus that were tested at low concentration [22].

Antihepatotoxic activity

C. esculenta leaf juice demonstrated hepatoprotective and antihepatotoxic activity. The hepatoprotective and anti-hepatotoxic studies were conducted against two well-known hepatotoxins paracetamol and CCl₄ using in vitro rat liver slice method. CCl₄ and Paracetamol generate free radical that causes oxidative stress. It also damages various cell organelles thus injuring the hepatocytes. The hepatoprotective efficacy was measured using the leakage of marker enzymes of liver function such as AST, ALP and ALT in the incubation medium. In presence of CCl₄ and paracetamol, there 22was an increase in the levels of marker enzymes. Insignificant changes were noted in the enzymes levels at one and two hour’s interval. At four hours interval, the marked elevations of toxicity marker enzymes were seen. However, the leaf juice of C. esculenta abnormally declined the leakage of AST, ALP and ALT in the medium demonstrating integrity of hepatocyte [23].

Antidiabetic activity

The antidiabetic activity of the ethanol extract of C. esculenta (EECE) leaves was carried out in rats using alloxan induced diabetes model. EECE (100, 200 and 400 mg/kg) and metformin (450 mg/kg) were administered orally in alloxan (120 mg/kg, i.p.) induced diabetic rats. At 4 h (96 mg/dl) the onset of reduction of blood glucose was observed, peak at 6 h (120 mg/dl) but anti-hyperglycaemic effect diminished at 24 h. Maximum reduction in blood glucose was observed (174.34 mg/dl) in subacute study, at the dose of 400 mg/kg on 14th day. These results suggested that EECE (400 mg/kg) exhibits antihyperglycaemic activity in alloxan induced diabetic rats [24,25].

Anti-lipid peroxidative activity

C. esculenta whole leaf juice has been reported to possess the free radical scavenging property. The in vitro free radical scavenging effect was studied on liver cells by using rat liver slice model [26]. The liver slices were incubated in presence of cytotoxic concentrations of CCl₄ and acetaminophen. The marked elevations and prevention of depletion of total tissue glutathione were observed in the presence of C. esculenta whole leaf juice [26].

Antimetastatic activity

Breast cancer mortality is primarily due to the occurrence of metastatic disease. The compound(s) that are derived from roots of the plant of C. esculenta has the capability to potentially and specifically inhibit tumor metastasis. It exhibited demonstrable activity in a preclinical model of metastatic breast cancer. Taro extract treatment also inhibited prostaglandin E2 (PGE2) synthesis and down regulated cyclooxygenase 1 and 2 mRNA expression. Taro extract modestly inhibits the proliferation of some, but not all, breast and prostate cancer cell lines and it completely blocks tumor cell migration [27].

Antifungal activity

Yang et al. evaluated the antifungal activity of taro along with molecular cloning and recombinant gene expression studies. CeCPI, a cysteine protease inhibitor (cystatin), was isolated from taro corm (Colocasia esculenta ). The result confirmed that recombinant CeCPI protein exhibited strongly cysteine protease inhibitor activity. Thus, the investigation clearly discovered a toxic effect of the plant on the mycelium growth of phytopathogenic fungi [28].

Anti-inflammatory activity

The ethanolic extracts of the leaves of C. esculenta possess antiinflammatory activity. The study was conducted in Wistar rats using the carrageenan-induced left hind paw oedema, carrageenan-induced pleurisy, and cotton pellet induced granuloma model. The results indicated that the ethanolic extract exhibits significant antiinflammatory activity when compared with the standard and untreated control [29].

Medicinal uses

C. esculenta has many medicinal applications as discussed earlier. All the plant parts viz. leaves, stem and tubers shows different medicinal properties. Some of the properties includes antimicrobial, antihepatotoxic, anti-diabetic, anti-lipid peroxidative action, antimetastatic, antifungal, anti-inflammatory and many more.

People of the Munda tribe, traditionally used corm of taro as a remedy for body ache. The juice extracted from corm of the plant is used in alopecia, as an expectorant, stimulant, appetizer and astringent. When cooked, the vegetable contains mucilage and found to be an effective nervine tonic. Table 2 summarizes chemical constituent and corresponding activity of C. esculenta plant parts.

Table 2: Chemical constituents and activity of different parts of Colocasia esculenta plant.

Pharmaceutical applications

The gum as well as starch obtained from the tuber of the C. esculenta plant can be used as an effective binder and mucoadhesive matrix forming agent [33].

Soumya et al. successfully prepared sustained release and evaluated matrix tablets of taro gum using metaprolol succinate as the model drug. The quantity of taro gum (X1) and polyvinylpyrrolidone (PVP) K30 (X2) were selected as independent variables. The time required for 90% of in vitro drug release was selected as the dependent variable. Tablets were prepared by direct compression and were evaluated for various post compression parameters such as tablet hardness, friability, weight variation, drug content and in vitro dissolution [34].

Another research paper by Arora et al. reported application of Taro gum in development of Mucoadhesive matrix tablets. Matrix tablets of Domperidone as a model drug was compressed using direct compression technique. This study showed concentration dependent mucoadhesive and release retardant potential of taro gum in the formulation of gastro retentive mucoadhesive matrix tablets [35].

Chukwu and Udeala studied the effectiveness of C. esculenta gum in poorly compressible drugs-paracetamol and metronidazole tablet formulations. The effectiveness of a polysaccharide gum obtained from the C. esculenta was evaluated comparatively with acacia and methylcellulose as binders in the formulation of poorly compressible drugs. At 4% w/w nominal concentration of Colocasia gum in metronidazole tablets and 6% w/w in paracetamol tablets showed very long disintegration time and prolonged release profile. The binders used for comparison yielded tablets that show better in vitro release characteristics [36].

C. esculenta polysaccharide can be used as a disintegrant in the formulation of orally disintegrating tablets. Its disintegrating property was reported to be comparable with that of the commercially available super-disintegrants.

Patents filed/published

Table 3 summarises different patents filed /published/granted involving Colocasia plant.

Table 3: List of Patents involving Colocasia plant.

C. esculenta is a largely cultivated plant used from ages as food and medicine. Flavonoids and triterpenoid’s are the two major therapeutically active groups of compounds found in the plant. Pharmacologically, the plant is antimicrobial, antihepatotoxic, antidiabetic, anti-lipid peroxidative, antimetastatic, antifungal and anti-inflammatory. There are also many pharmaceutical applications for the plant.

There is a lot of scope for usage of C. esculenta in pharmaceutical industries as well as in research work. Herbal formulations consisting of plant extracts from different parts of plants can be developed for many ailments as discussed in this paper. More research work can be done on structural investigation and applications of the gum obtained from C. esculenta . The starch and the gum obtained from the tubers can be commercially made use of in pharmaceutical industries in form of binder, matrix forming agent, thickening agent etc. Thus, there is need to explore this plant so as to make use of its medicinal and pharmaceutical properties to its fullest.

The author(s) declare that there is no conflict of interests regarding publication of this article.

Authors are very much thankful to the Principal, Hyderabad (Sindh) National Collegiate Board’s Dr. L. H. Hiranandani college of pharmacy, Ulhasnagar for his continuous support, guidance and encouragement.