Traditional uses, phytochemistry and therapeutic efficacy of cassava ( Manihot esculenta Crantz) - A Review

The usage of naturally available resources by humans for gratifying different requirements is an age - old custom. This is because natural products provide indispensable facilities in the form of nutritional, economic, social, medicinal aspects and many more. Cassava ( Manihot esculenta Crantz) has been used as a herbal medicine by different groups of ethnic people. Besides having medicinal prospect, this plant is commonly used as a source of nutrition for humans and animals in tropical regions. However, conduction of more studies are required to see if there is chemical, microbiological, and/or clinical evidence, from a scientific perspective, of their effectiveness for those ailments. Therefore, this review was conducted to summarize the traditional uses, to understand the phytochemistry and identify the possible correlation between bioactive compounds and corresponding pharmacological properties. A systematic and detailed literature search has been undertaken for the study by using standard search engines like Google Scholar, PubMed, SciFinder, Research Gate and Science Direct. The evidential information was then assembled to present the manuscript with separate sections. From the literature search, it came into focus that Cassava contains various secondary metabolites which exhibits some notable pharmacological activities like antioxidant, antiradical, anticancer, antibacterial, antifungal, antidiarrheal, analgesic and pesticidal activity. The biological activities established by cassava provide insight into its usage in traditional medicinal systems. But an intricate and thorough review appears to be deficient on M. esculenta. Therefore, this review has summarized the studies investigating about the traditional uses, phytochemistry, bioactive compounds and therapeutic efficacy of M. esculenta . The significance of this review is aimed at a better understanding of the novel applications and further considerations for more logical and scientific evaluation. We hope this study will further aid in the development of research on this area to identify a new generation of natural source - based treatments that will help meet the growing consumer demand for safe, sustainable, and natural treatments.


Introduction
Manihot esculenta Crantz is an edible dicotyledonous perennial plant belonging to the family Euphorbiaceae (2).It is a semi-woody shrub that originated in South America.M. esculenta is commonly known as cassava, tapioca, sweet potato tree, Brazilian arrowroot and by different local names in different parts of the world (Fig. 1).It is being widely cultivated in tropical and subtropical regions of the world as it acts as a reservoir of carbohydrates in tropical regions.Cassava leaf is a native edible vegetable and it is also a potential alternate source of protein for both humans as well as animals (3).Cassava leaves are an enormous source of proteins, carbohydrates, vitamins and minerals (4,5).Besides having nutritional value, M. esculenta is an integral part of folk medicinal practice.It is used for treatment of different health conditions indigenously (6).
Apart from having medicinal properties, Cassava is also consumed as staple food by people in Ghana, Africa as it serves as source of stored carbohydrates in its roots, leaves and tubers.Cassava besides being an important part of diet amongst African population also has economic importance as almost half of the world's cassava estimating nearly 86 million tons is produced in Africa (7).Therefore, this review aims to make a proper and systematic documentation of the indigenous uses, phytochemistry, identified active components, pharmacological efficacy of Manihot esculenta as these will provide a new perspective in future novel investigations for drug development.
A systematic literature search was performed using scientific databases such as PubMed (https:// pubmed.ncbi.nlm.nih.gov/),Google Scholar (https:// scholar.google.com/),SciFinder, Research Gate (https:// www.researchgate.net/),Science Direct.The search terminologies like "indigenous uses of cassava", "secondary metabolites present in cassava", "isolated compounds from Manihot esculenta", biological activities reported in Manihot esculenta" were used for critical analysis of the works being done earlier.A total of 52 articles were found to be relevant to the area of interest.The published works having constructive and useful information relevant to the review was selected and the manuscript was summarized with separate sections assembling all the applicable data.Based upon the analyses of data obtained from selected articles, we formulated several important findings which are a summary shown in tables.

Morphology of the plant
Manihot esculenta is a shrub having yellowish grey smooth bark.It grows upto an average height of 4m.Leaves are dark green above and pale yellowish below and show an alternate arrangement.The inflorescence is lax with 3 to 5 together in fascicles.Male flowers are greenish-white in appearance with reddish-white bands inside.The anthers are yellow and disc is yellow to light orange in appearance.Female flowers are perianth green with red margin and midrib and the ovary contains 6 longitudinal ridges (1).

Distribution
The plant is native to Brazil and now is found throughout tropical regions.In India, it is found in Maharashtra, Karnataka, Kerala, Tamil Nadu and in North Eastern India particularly in Assam, Meghalaya (1).

Traditional uses of Manihot esculenta
Manihot esculenta is traditionally consumed as a primary green vegetable in different countries like Latin America, Philippines, Indonesia, Malaysia and some other Asian countries (8,9).It is an important part of the Nigerian traditional medicinal system.The leaves and seeds of M. esculenta are being used to treat different types of ailments traditionally to meet up with health challenges from ancient times (Table 1).The leaves and seeds are traditionally used for curing fever, headache, rheumatism, and hemorrhoids (6).In Nigerian folk practice, M. esculenta is utilized as a remedy for ringworms, tumor, conjunctivitis, sores and lesions (6).Some literature citation has also reported the therapeutic use of M. esculenta leaves in hypertension, aches, irritable bowel syndrome, cancerous affections and dysentery.The leaves are also employed as an effective remedial agent in flu, marasmus, snake bites, prostatitis, spasms, and as an antiseptic, diuretic, cyanogenetic and demulcent herbal agent (10-12) (Table 1).

Phytochemistry of Manihot esculenta
The pharmacological activity of medicinal plants is mainly contributed by secondary metabolites present in them.These secondary metabolites are of different classes namely alkaloids, glycosides, flavonoids, tannins, terpenoids, proanthocyanidins, furocoumarins, naphthodianthrones, proteins, and peptides (13).The leaves of Manihot esculenta has been reported to contain alkaloids, flavonoids, phenols, tannins, terpenoids, anthraquinones, phlobatannins, saponins, reducing sugars, anthrocyanosides.The presence of cyanogenic glycosides such as lotaustralin and linmarin, noncyanogenic glycosides, hydroxycoumarins has been reported in the fresh leaves of Cassava and in its roots (14)(15)(16)(17).Besides this, the plant is also rich in different types of macro and micronutrients and contains antioxidants like â-carotene, vitamins like vitamin A and C (3,18,19) (Table 2).

Pharmacological activity
As per the literature survey, different parts of Manihot esculenta have some significant pharmacological activities like antioxidant, antiradical, anticancer, antibacterial, antifungal, antidiarrheal and analgesic while extracted with different solvents (Table 3).

Antioxidant activity
A study was carried out to analyze antioxidants present in Indian Cassava.The study focused on the extraction of total phenolic content, anthocyanins and other flavonoids.Three different solvents (acidified methanol, methanol and acetone) were used for the extraction of total phenol and anthocyanins.The acidified methanolic extract yielded the highest quantity of anthocyanin whereas acetone extract yielded the highest total phenol contents.
The antioxidant assays carried out demonstrated that all the extracts have emerged as good scavengers of free radicals contributed by H + ion (22).In a similar study, it was reported that the aqueous leaf extract of Manihot esculenta has markedly decreased the production of lipid hydroperoxides in a dose-dependent manner.The extract sufficiently minimized formation of volatile markers of lipid peroxidation such as ethylene which was measured using gas chromatography.Furthermore, the use of the Fluorescence technique revealed that the extract reduced the cellular production of ROS by activating monocytes in HL-60 cells (23).Additionally, the ethanolic leaf extract of M. esculenta exhibited mild DPPH scavenging activity and significant superoxide activity against NBT.The extract also showed moderate xanthine oxidase inhibition activity and very low pancreatic lipase inhibitory potential (24).

Antiradical activity
The aqueous leaf extract of Manihot esculenta showed a remarkable antiradical activity.The extract demonstrated inhibitory effects about 55% and 49% in non-heated and boiled sample respectively.In comparison to aqueous extract of Pteridium aquilinum, Abelmoschus esculentus, Hibiscus acetosella, M. esculenta has shown a maximum inhibitory efficiency in a concentration dependent manner without much significant difference.The production of intermediate peroxyl and different free radicals by different extracts in the study was measured by ESR technique using POBN as a spin trap agent (23).

Anticancer activity
The anticancer activity of crude methanolic and aqueous callus extracts of Manihot esculenta against breast carcinoma cell lines (MCF7) was also evaluated.Agarose gel electrophoresis and flowcytometry was used to assess the DNA damage intoxicated in breast cancer cell line.The result showed that the methanolic and aqueous callus extract of M. esculenta had demonstrated cytotoxic activity at the dose of 0, 2.5, 5, 10, 20 µg/mL by inhibiting the growth of treated breast carcinoma cells as compared to the untreated cells.During the study, IC50 values for methanolic and aqueous extract were found to be 1.43

Antibacterial activity
The ethanolic leaf extract of Manihot esculenta reported antibacterial activity against specific bacterial strains such as E. coli (T.Escherich, 1885-Enterobacteriaceae), Klebsiella pneumoniae (Schroeter, 1886-Enterobacteriaceae), Pseudomonas aeruginosa (Schroeter, 1872-Pseudomonadaceae), Staphylococcus aureus (Rosenbach, 1884-Staphylococcaceae) and Bacillus subtilis (Ehrenberg, 1835-Bacillaceae).The extract showed maximum zone of inhibition of 8.1mm against Pseudomonas aeruginosa at the concentration of 250 mg/ml and no inhibition zone was shown by the extract at any concentration (5, 50, 100, 250 mg/ml) against E. coli (26).In a similar finding, it was observed that the methanolic extract of Cassava leaf showed maximum activity against Staphylococcus aureus by forming a zone of inhibition of 16 mm while the least activity was reported in the acetone extract against Pseudomonas aeruginosa (2.5 mm) (27).Another work on hydroethanolic extract of M. esculenta showed the effect only on P. aeruginosa meropenem resistant at the concentration of 500 µg/mL whereas it failed to show any effect against S. aureus (33).

Stem Aqueous Methanol In vitro
The result showed that the methanolic and aqueous callus extract of M. esculenta had demonstrated cytotoxic activity at the dose of 0, 2.5,5, 10,20 µg/ml by inhibiting the growth of treated breast carcinoma cells as compared to the untreated cells. ( Leaves Ethanol

In vitro
The extract showed maximum zone of inhibition of 8.1mm against Pseudomonas aeruginosa at the concentration of 250 mg/ml and no inhibition zone was shown by the extract at any concentration (5, 50, 100, 250 mg/ml) against E. coli (

Leaves Methanol In vitro
The methanolic extract of cassava leaf showed maximum activity against Staphylococcus aureus by forming a zone of inhibition of 16mm while least activity was reported in the acetone extract against Pseudomonas aeruginosa (2.5 mm)

Leaves Hydroethanol
In vitro Hydroethanolic extract of M. esculenta showed the effect only on P. aeruginosa meropenem resistant at the concentration of 500 µg/ml whereas it failed to show any effect against S. aureus

In vivo
The ethyl acetate extract showed higher pesticidal activity of 95% at high dose after 48 hr and 97% at the same dose after 72 hr than ethanol and petroleum ether extracts Table 3. Pharmacological Activities of different extracts of Manihot esculenta Source: Self-compiled from different published works as cited.

Antifungal activity
The antifungal efficacy of M. esculenta was investigated against pathogenic fungi Aspergillus niger (Van showed a reduction of pain in mice that was induced by 0.6% acetic acid.The analgesic power was highest at 25.6 mg/kg body weight concentration showing a 73.94% increase in writhing protection.Surprisingly, the extract showed lesser analgesic activity of 62.14% at a dosage of 51.3 mg/kg body weight and 55.9% at a higher dose of 102.6 mg/kg body weight (6).

Pesticidal activity
The leaf extract of Manihot esculenta was found to be highly toxic against the red flour beetle (Tribolium castaneum) which is a worldwide pest of stored food grains.Extracts were prepared in three different solvents (petroleum ether, ethanol and ethyl acetate) and were tested for pesticidal activity at different concentrations (150 ppm, 300 ppm, 500 ppm) at three-time intervals (24 hr, 48 hr, 72 hr).All three extracts have shown promising mortality rate of pests in a dose and time dependent manner.After 24 hr, ethyl acetate showed highest mortality (82%, 89% and 93% at 150, 300 and 500 ppm) and petroleum ether extract showed lesser mortality (50%, 70% and 83% at 150, 300 and 500 ppm).Whereas ethanol extract showed medium mortality (62%, 78%, 87% at 150, 300 and 500 ppm).The ethyl acetate extract showed higher pesticidal activity of 95% at a high dose after 48 hr and 97% at the same dose after 72 hr than ethanol and petroleum ether extracts (29).
The existing literature related to Manihot esculenta showed that they involve studies on a particular biological property or its effect against a particular disease.But a precise and in-depth review of the indigenous uses, phytocompounds present and their relationship with pharmacological efficacies is not done.This study has tried to address all the prospects with a special focus on scientifically validated uses, screened and isolated metabolites and therapeutic properties.From the literature study, it is well understood that different parts of the plant have folklore uses and many of them are evidentially proved.M. esculenta has testified phytochemicals like alkaloids, flavonoids, phenols, tannins, terpenoids, anthraquinones, phlobatannins, saponins, reducing sugars and anthrocyanosides in different solvents.Most of the phytocompounds present in the plant are identified from M. esculenta stem (coniferaldehyde, isovanillin, 6-deoxyjacareubin, scopoletin, syringaldehyde, pinoresinol, p-coumaric acid, ficusol, balanophonin, ethamivan), M. esculenta leaves (coumarin, scopolin, scopoletin, aglycone and flavonoids namely Kaempferol-3-O-rutinoside and rutin) (20).The plant has displayed a spectrum of medicinal benefits including antioxidant, antiradical, anticancer, antibacterial, antifungal, antidiarrheal, pesticidal and analgesic.

Conclusion
The findings specify that plants are endowed with useful properties that can be harnessed inexpensively.Nowadays, plant-based products are in higher demand because of the fact that synthetically derived products possess the capacity to luster a harmful impact on humans as well as on the entire ecosystem.This review indicates that Manihot esculenta is a less acknowledged medicinal plant having enormous nutritional as well as pharmaceutical properties.All the researches have scientifically manifested the use of the plant in folk medicinal practice in different parts of the world.However, there are still many traditional uses of this plant which needs detailed scientific finding so that a clear and genuine validation of the uses is established.Moreover, the bioactive compounds isolated from the plant also require an elaborative pharmacological screening for their potent biological properties.There is also a lack of information on the safety aspect of the plant which urges for performing toxicological studies on extracts, and isolated secondary metabolites from M. esculenta.

Fig 1 .
Fig 1.The plant Manihot esculenta in its natural habitat

Table 1 .
The plant Manihot esculenta in its natural habitat Traditional uses of different parts of Manihot esculenta Source: Self compiled from different published works as cited.