Production and optimization of bioethanol from sour orange (Citrus aurantium) peel using baker’s yeast

Abstract

-Usage of fossil fuel has been known to cause adverse effects on the environment due to the emission of harmful greenhouse gases. Production of bioethanol from biodegradable waste material could be an alternative fuel system to the expensive petroleum products. The objective of the study was to determine the suitability of sour orange peel as an effective substrate for bioethanol production using baker’s yeast (Saccharomyces cerevisiae). The sour orange peel extract was inoculated with Saccharomyces cerevisiae with the fermentation media composed of 100 g/L sucrose, 5 g/L yeast extract, 10 g/L KH2PO4, 2 g/L (NH4)2SO4, and 0.5 g/L MgSO4·7H2O in order to produce ethanol at room temperature for 24 hours. Ethanol content produced from fermented sour orange peel was measured by an Ebulliometer. Initially the amount of ethanol produced from the orange peel extract was 5% (v/v) at room temperature (30±2 °C) after 24 hours of fermentation. When different inoculum size such as 0.5, 1.0, 1.5 and 2.0 g /100mL were used in the fermentation media, ethanol production was increased to 5.25% when inoculum size of 1.5 g /100mL was used. When different carbon sources such as glucose, maltose, sucrose and lactose were used in the fermentation media, ethanol production was increased to 5.5% in media containing maltose. After the optimization of culture conditions such as fermentation time (24 hour) temperature (37oC) and pH (5.0), the production of ethanol was significantly increased to 6.5% in sour orange peel medium. When different nitrogen source such as ammonium sulphate, ammonium nitrate, ammonium chloride or urea was used in the fermentation media, ethanol production was significantly increased to 7.5% in orange peel media containing ammonium nitrate. The current study concludes that 7.5 % (v/v) ethanol (1.5 times higher) can be produced from sour orange peel using baker’s yeast under optimized conditions including maltose as the C source and ammonium nitrate as the N source. Large scale fermentation study should be carried out with bioreactor to determine whether this finding could be commercialized.