Phytochemical screening and in-vitro evaluation of pharmacological activities of peels of Musa sapientum and Carica papaya fruit

Abstract Aqueous, absolute and 80% ethanolic extract of fruit peels of Musa sapientum and Carica papaya were investigated for their antibacterial activity, measured by disc diffusion method and antioxidant activity, measured by four different methods. Papaya and banana peels were found to contain terpenoids, tannins, alkaloids, saponins steroid, phenols, fixed oils and fats. 80% ethanolic extract of banana peel was found to contain highest total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity but in papaya peel, highest TPC and reducing activity was shown by water extract while, TFC and radical scavenging activity was given by 80% ethanolic extract. In banana, water extract showed highest antibacterial activity against tested bacteria while in case of papaya, absolute ethanolic extract showed highest antibacterial activity. The present study revealed that peels of banana and papaya fruits are potentially good source of antioxidant and antibacterial agents.


Introduction
Human beings, plant and animal wastes are biodegradable. Fruit wastes like peel of some of the fruits were found to contain even higher concentration of valuable active constituents as compared to other plant parts (Yan et al. 2006). Peptic ulcer can be effectively cured with the help of isolated compounds such as alkaloids, flavonoids and terpenoids (Jain 2016). Bananas are one of the most popular and highly consumed fruit in the world. Pharmacologically, Bananas are used for the treatment of diarrhoea, dysentery, ulcerative colitis and certain other diseases (Khare 2007). Many pharmacologically active constituents like saponins, glycosides, tannins, phenols, steroids and flavonoids were detected in methanolic extract of Musa acuminate flowers (Sumathy et al. 2011).
Carica papaya is an herbaceous fruit crop that has very high nutritive value. C. papaya is an excellent source of vitamins and nutrients. C. papaya prevents cataract formation, constipation, nausea, hypertension and chronic obstructive pulmonary disease. C. papaya leaves contains carpine that have good antioxidant activity (Nwinyi & Anthonia 2010;Aravind et al. 2013). Aqueous extract of C. papaya seeds were found to contain more antioxidant potential than fruit (Zunjar et al. 2015). Fruit peels are usually discarded as waste material. Studies have revealed the presence of important phytochemical constituents in fruit peel (Oloyede 2005;Imam et al. 2011) so this project was planned to evaluate the antioxidant and antibacterial activities of different banana and papaya peel extracts.

Phytochemical screening
Plant kingdom has a good resource of active constituents valuable in the dealing of many intractable diseases. Phytochemical analysis was carried out on different extracts of banana and papaya peel that confirmed the presence of certain medicinally important phytochemical constituents such as terpenoids, tannins, saponins, alkaloids, phenol, steroids, proteins and fixed oils. This was co-related with the previous work which confirmed the presence of tannins, saponins, steroids and alkaloids in Musa sapientum and tannins, saponins, cardenolides in C. papaya pulp (Oloyede 2005;Imam et al. 2011). Alkaloids, flavonoids and saponins had antibacterial whilst alkaloids, tannins and phenols found to have antioxidant potential (Ghasemzadeh et al. 2010).

Antioxidant activity
Total phenolic content (TPC) and total flavonoid content (TFC) in different extracts of banana and papaya peel are shown in Figure S3(A) and (B). The concentration of phenolic contents was much higher in banana extracts but flavonoid contents were present in higher concentration in papaya fruit peels. Highest TPC in 80% ethanolic extract of banana peel and highest TFC in 80% ethanolic extract of papaya peel indicated that maximum phenolic and flavonoid extraction were done in the presence of combination of aqueous and organic solvent and these results are similar to the results of previous study (Sultana et al. 2009). The flavonoid contents in Musa sapientum peels were higher than that of Musa acuminate banana peel extracts (Azizuddin et al. 2015).
Different extracts of banana and papaya peel were subjected to investigate their antioxidant potential using two methods (DPPH and Ferric reducing activity). Figure S3(C) showed that banana peel extracts have better capacity to scavenge free radical as compared to papaya peel extracts. In case of 80% ethanolic extract of banana peel, a direct relation was observed in the TPC, TFC and DPPH radical scavenging activity. This finding also indicated that total phenolic and flavonoid contents are directly involved in radical scavenging activity. Early findings of a study also showed this direct relationship (Lee et al. 2003). Figure S3(D) shows ferric reducing activity in different banana and papaya peel extracts. Distilled water extract of papaya and 80% ethanolic extract of banana were found to contain highest reducing power activity and these extracts also contained highest TPCs as compared to other tested extracts. This confirmed that there is a positive relationship between phenolic contents and reducing power activity and this finding is in accordance with early findings of a study (Stratil et al. 2006). Antioxidant potential of reference standard (BHT) was significantly higher as compared to antioxidant potential of all tested banana and papaya peel extracts.

Antibacterial activity
Antibacterial activity of different extracts of banana and papaya peel extracts were investigated against four bacterial species using disc diffusion method. Results of this study showed that all papaya and banana peel extracts were active against all tested bacteria (S. aureus, B. subtilis, P. aeruginsa, E. coli) (Table S1). But highest antibacterial activity was shown by water extracts against most of the tested bacteria, this slightly higher activity of water extract may be due to the presence of saponins and alkaloids in this water extracts that was not found in ethanolic extracts of banana. In contrast, absolute ethanolic extract of papaya peel have highest antibacterial activity as compared to other tested extracts this might be due to the fact that active constituents have good solubility in organic solvents like ethanol (de Boer et al. 2005). These results of antibacterial activity of banana were in agreement with previous studies which showed that aqueous extract of Musa acuminate has antibacterial activity against different bacterial species (Chabuck et al. 2013).

Conclusion
Results of this study demonstrated that Musa sapientum and C. papaya might be a good source for the production of new antibacterial and antioxidant agent for the treatment of different diseases. However, there is need of further studies to isolate and identify the active constituents responsible for antibacterial activity of banana peel.