Production and Spectrophotometric Quantification of Bioethanol from Pineapple Fruit Skin

This study investigated the potentials of pineapple waste (fruit skin) as an alternative and cost-effective lignocellulose for bioethanol production by Zymomonas mobilis and Saccharomyces cerevisiae. The substrate was pretreated using dilute hydrochloric acid (HCL) to alter the complex structure of the carbohydrate polymers to removing lignin and hemicelluloses, reduce cellulose crystallinity and increase the porosity of the materials. Enzymatic hydrolysis was carried out to further depolymerize the cellulose component to simple sugars. Hydrolysis and fermentation lasted for five days. Fermentation parameters such as pH, temperature, reducing sugar (brix level) and specific gravity were monitored for five days. The concentrations of reducing sugar (brix level) were calculated based on the relationship: Brix = 261.3×(1–1/S.G).The specific gravity of the wort was determined before and during fermentation using the specific gravity bottle of known weight. The pH and temperature of the wort was determined using calibrated HANNA multi parameter probe (HI9811-5) while ethanol content was determined spectrophotometrically using acid dichromate solution. The specific gravity, pH, temperature and reducing sugar of each of the substrates decreased as the fermentation time increases. The substrate recorded a total reducing sugar content of 17.5mg/ml. The pH of the broth for the substrate decreased during the five days fermentation period with optimum pH for ethanol production ranging from 4.9 to 5.2 for the yeast and 5.0 to 5.8 for the bacterium at 72hrs incubation. Fermentation using S. cerevisiae was slow and required three days to complete with maximum ethanol yield of 51%. The fermentation with Z. mobilis proceeded very rapidly and was completed in three days with maximum ethanol yield of 78%. Sugar utilization was faster in Z. mobilis than in S. cerevisiae with a corresponding increase in ethanol yield. Conclusively, Z. mobilis could be considered a better microorganism for bioethanol production.