Banana Sap, a Resource Material for Bioethanol Production and other Value Added Products

Abstract

Bananas (Musa spp.) are commonly grown in tropical and subtropical nations, and each hectare of a banana plantation generates approximately 220 tons of biomass waste. About 4-5 m3 of sap are produced from one tonne of dried banana pseudostem, due to its high chemical oxygen demand (COD) and biological oxygen demand (BOD). Banana pseudostem contains nearly 90% of moisture. In this study, the potential of utilizing banana sap from pseudostems as a feedstock for ethanol production has been investigated. Furthermore, antibacterial, antioxidant, and anticancer activities of banana sap and crude extracts were examined, followed by LCMS analysis. Concentrated banana sap was combined with other industrial by-products such as corn steep liquor (CSL), spent wash (SW), and yeast extract (YE) for ethanol production followed by acid and alkali hydrolysis to enhance the sugar levels in the sap. Fermentation is carried out using the MTCC170 and MTCC180 strains of Saccharomyces cerevisiae. Concentrated banana sap augmented with 25% SW (v/v) and MTCC170 produces 16-fold higher amount of ethanol (2.5 g L −1) than banana sap alone. Alkali-hydrolyzed banana sap supplemented with 25% SW contains high ethanol than the control. These findings indicate that banana sap, when combined with other industrial by-products, can be employed as a sustainable source to produce ethanol. The antibacterial potential of oxidised and un-oxidized banana sap against a microbial test panel comprising of gram-positive and gram-negative bacteria, and Candida albicans, by in vitro microbroth dilution method was evaluated. The minimum inhibitory concentration (MIC) of unoxidized banana sap exhibited a potent anti-bacterial activity which ranged from 15.625 to 62.5 mg/mL. By using the DPPH technique, the in vitro radical scavenging activity of dichloromethane (DCM) and ethyl acetate extract (EA) of banana sap showed 54.62 ± 1.09% and 79 ± 1.05% of antioxidant activity at the concentration of 1 mg/mL, respectively. Human breast cancer cell line proliferation (MCF-7) was inhibited to the greatest extent by the DCM extract of banana sap at a concentration-dependent decrease in a proliferative index, indicating a cytotoxic effect. The IC50 values were calculated and found to be 34.15±8.75 μg/mL. Cytotoxic effect of the banana sap extract increased significantly with increasing concentration, but the EA extract showed inconsistent results, revealing no cell growth inhibition. Additionally, LCMS investigations identified the presence of bioactive components as dihydrorescinnamine, epimedin A, and rescinnamine derivative in DCM and EA extract of banana sap. The findings of the present research indicated that banana sap is a potential source of bioactive substances with useful antibacterial, antioxidant, and anticancer activities.