Functional, nutritional and medicinal potential of banana peel

Banana, botanically called Musa spp. is among the most cultivated and consumed fruits, which generates a huge amount of waste (peel) annually. The current review was to combine the activities and beneficial aspects of banana peel. The organic composition of banana peel comprising lipids, fibers, carbohydrates and protein which results in presence of several bioactive molecules. The literature revealed that these bioactive compounds including alkaloids, flavonoids, phenolics, steroids (tannic acid, catechol, β-sitosterol, ferulic acid) help to perform different biological activities and cures antitumor, antiparasitic, antibacterial, antifungal, antiaging, antioxidant and antiviral activities. The mechanism of its bioactive compounds helps to cure infections and diseases. The study states that banana peel is a valuable byproduct which has several benefits and it can be used in different industries like pharmaceutical, cosmetics, food, lather, biodiesel and bioethanol.


Introduction
Banana (Musa spp.) is one of the most commonly eaten fruits with considerable nutritional value [1].In tropical and subtropical zone, this crop is widely grown and consumed.Most of this fruit is consumed fresh, but it can also be processed into a variety of products at large scale, including dried fruit, chips, smoothies, ice cream, bread, flour, wine, and ingredients for functional cuisine

Nutritional composition of banana peel
Banana peel is a cheap source of starch, crude lipids, proteins, dietary fibers and polyunsaturated fatty acids, especially linoleic and alpha-linolenic acid, pectin, minerals and essential amino acids (Table 1).
It contains amino acids including lysine, leucine, valine, phenylalanine and threonine they are all approved to be higher than Food and Agricultural Organization (FAO) standard except lysine (

Antioxidant potential of banana peel
Antioxidants are substances that neutralize free radicals and can be obtained from food.Dietary antioxidants play a vital pharmacologically role in improving male reproductive health, reducing insulin resistance and lowering the risk of type II diabetes [79,80].Antioxidants promote normal biological functions including healthy cell proliferation, immunological support and molecular degeneration prevention, including the prevention of premature ageing [81].The banana should be regarded as a useful dietary source against diseases and an excellent source of natural antioxidants for foods.These compounds predominate in the majority of the tissues in banana peel [82].The banana peel extract was found to contain gallocatechin which demonstrated significant antioxidant activity.Shinichi et al. [83] revealed in her study that peel contained higher gallocatechin (158 mg/100g DW) than pulp (29.6 mg/100g DW).It was also more potent than the banana pulp extract against lipid autoxidation.Catechins show strong antioxidant effects against lipid peroxidation [84] and protective effects against diseases such as cancer and CVD [85].Antioxidant capacity depends on different solvents such as acetone, acetyl acetate, chloroform, ethanol, methanol and n-hexane by several antioxidant potential determining assays including diphenyle-1-picrylhydrazyl assay (DPPH), ferric reducing antioxidant power (FRAP), metal chelating activity, 2,2'-azinobis (3-ethylebenzothiazoline-6-sulfunic acid assay (ABTS), superoxide anion scavenging activity (SOSA), nitric oxide radical scavenging activity (NORSA), hydroxyl radical (OH) scavenging activity, lipid peroxidation inhibition capacity (LPIC), total phenolic content (TPC) total flavonoid content (TFC), total carotenoid contents (TCC) and radical scavenging activity as mentioned in (Table 5).Flavonoid's antibacterial mechanisms of action prevent the production of nucleic acids, cytoplasmic membrane function, metabolic activity, adhesion and biofilm generation, altering membrane permeability which reduce the pathogenicity of microbes.Tannins prevent bacterial extracellular enzyme activity and interfere with bacterial metabolism by preventing oxidative phosphorylation [111].
Saponins increase the cell membrane permeability.This rise leads to the cell membrane being unstable and ultimately causing cell hemolysis.Similarly, alkaloids and triterpenoids break down lipid components and increase their permeability, causing the cell membrane to lyse or the cytoplasm of bacterial cells to coagulate (Fig. 3) [112].As mentioned in (Table 6), previous studies found that banana peel's antibacterial capabilities were efficient against a variety of microbes.Therefore, the main therapy recommendations focus on increasing the synthesis of substances that protect the stomach mucosa in addition to restricting acid secretion, thereby preventing epithelial erosion [135].Peptic ulcer prevention or treatment is one of the most difficult medical issues since gastric ulcer therapy has downsides and the majority of medications on the market today have limited effectiveness against stomach disorders and are frequently linked to serious adverse effects.In particular, in the treatment of peptic ulcers in various experimental models for the evaluation of anti-ulcer medications, the research of natural products and medicinal plant extracts has emerged as one of the most fascinating and attractive sources of innovative therapy for various gastrointestinal problems.Additionally, they observed the protective effects of the banana peel on gastric mucosa due to its several bioactive ingredients including essential phytochemicals and micronutrients such alkaloids, carotenoids, flavonoids, lignans, phenolics and tannins.

Mechanistic characteristics of bioactive components may inhibit ulcer through a number of mechanisms, including antioxidant activity, repression of cell growth, activation of apoptosis, repression of cell invasion and intracellular signaling pathways [86].
The remarkable antiulcer activity and cytoprotective properties of the extract of banana peel (Musa paradisiacal) on the experimental organisms may be attributed to the phytochemicals such as flavonoids, tannins and saponins [136].Leucocyanidin, a naturally occurring flavonoid, reportedly preserves the gastrointestinal mucosa from erosions [137].Leucocyanidin and its synthetic derivatives, hydroxy ethylated leucocyanidin and tetraallyl leucocyanidin, were reported to protect the gastric mucosa in rat models of aspirin-induced erosions by thickening gastric mucus [138].Literature indicated that research has been done on laboratory animals (rats and mice).The peel extract has been tested on different acute ulcer models including Alcohol-induced gastric ulcer (AL) in rats [139], Aspirininduced gastric ulcers (ASP) in rats [140]

Conclusion and future prospects
Based on previous information, the banana peel has great biological potential.Concerning nutritional content, the peel can be considered a cheap viable source of dietary fiber because it contains a high amount, which promotes healthy digestion of food.Many studies have proved that banana peel contains high antioxidant and bioactive content that could help the pharmaceutical sector to prevent chronic diseases and increase interest in enhancing food quality.It might provide consumers with a better understanding of the production of valueadded products.On the other hand, several molecular processes, such as metabolomics, genomics and proteomics, enable us in determining the mode of action of several bioactive chemicals to treat a wide range of unclear diseases or infections.Apart from excellent antioxidant sources and high nutritional values for preventing and treating chronic diseases, literature has shown that banana peel may also be used to produce cost-free energy in the form of bioethanol, biodiesel, organic acids, single-cell protein and various important industrial enzymes.some studies have advocated that peel can be used for skin treatment because of its high antimicrobial potential, which may open a new site for the cosmetic industry.Raw banana peel can be transformed into edible food to avoid its unpleasant taste and increase its consumption.

Authors' contributions
[2-4].Literature indicated, Southern Asian tropical regions are where bananas were first domesticated; today, 130 nations grow bananas.Banana production has significantly expanded globally over the last 20 years.The average annual output of bananas worldwide has increased from 69 million tons in 2000-2002 to 116 million tons in 2017-2019, in which India stands first with a production of 32 million metric tons annually (Fig. 1) [5].Pakistan has produced 154,800 tons of bananas from 34,800 hectares on average.Sindh province of Pakistan has the major share with 87 % of total area followed by Khyber Pakhtunkhwa (KPK), Punjab and Balochistan [6].The genus Musa of the family Musaceae includes a wide range of hybrids.According to published reports, there are almost 30 different varieties of banana present all over the world [7].Whereas the Musa spp. is further diversified into different four sections namely Eumusa, Rhodochlamys, Australimusa and Callimusa.Among these sections, the most widespread section geographically is Eumusa and it is followed by Australimusa.The edible class of bananas is solely from Musa accuminata [8].Pakistan produce different verities of bananas among which 95 % of area is under Basrai variety (Cavendish dwarf), whereas other common verities are William Hybrid, Grand Nine (G-9), Chinese varieties B-10, W-11 and Pashing [6].Banana sector has low yield and is less profitable in Pakistan than that of other neighboring banana-growing countries.Pakistan's banana fruit yield is facing several challenges in which the most significant challenge is prevalence of banana pathogen epidemics and the lack of high yielding varieties that are compatible with the changing climate.Conserving infected suckers, lack of healthy disease-free suckers, prevalence of single low yield variety, poor crop management, skills and technology, water scarcity, fertilizers and post-harvest losses are other challenges [9].

Figure 3 :
Figure 3: Antimicrobial strategy of banana peel

Table 3 : Mineral composition of banana and plantain peel [51] Minerals Peel (mg/100g) Plantain (mg/100g)
Violaxanthin is a food colorant while neoxanthin is an intermediary in the generation of the plant hormone abscisic acid [62], cryptoxanthin is used as a food colorant and might reduce the risk of lung cancer [54].Serotonin may play a role in sensations of happiness and well-being [63],

Table 6 : Antibacterial potential of banana peel Microorganisms Extraction solvents Zone of inhibition (mm±standard deviation) References
Gu C, Mao X, Chen D, Yu B & Yang Q (2019).Isoleucine plays an important role for maintaining immune function.Curr Protein and Pept Sci 20(7): 644-651.