Production of Bioethanol from Fruit Wastes (Banana, Papaya, Pineapple and Mango Peels) Under Milder Conditions

Abstract

A very huge amounts of fruit wastes are available as sugar laden wastes world over. In fact, there is a need to recover value added products from these wastes. Fruit wastes are rich in sugars and carbohydrates which can be recovered and utilized for the production of bioethanol. Gasoline is being used at very huge scales globally. Therefore, plenty of bioethanol would be required to be produced if bioethanol has to replace gasoline as a fuel. Present studies are directed towards finding cost effective ways to recover sugars from fruit wastes starting initially without using any acidic or enzyme catalysts. In the present studies fruit wastes, such as, peels of banana (BP), pineapple (PAP), papaya (PP) and mango (MP) were used. The studies were aimed to find out the potential of these fruit wastes to produce total reducing sugars (TRS), pentose sugars (PS) and bioethanol. Simple soaking in water and steaming resulted in the recovery of free sugars. Enzymatic hydrolysis using cellulase and xylanase enzymes was found to show good yields of total reducing sugars and pentose sugars. BP and PAP were found to be the potential candidates for the production of bioethanol. In comparison to the enzymatic hydrolysis, the acidic hydrolysis using dilute H2SO4 was found to give higher yields of TRS and PS from fruit wastes in shorter times. However, the enzymatic hydrolysis was found to be a better choice for the production of bioethanol from the BP and PAP hydrolysates in order to avoid the inhibitory effect of yeast toxicants produced. Since the pretreatments by using costly chemicals are the costly steps in the enzymatic hydrolysis of biomass the presently developed pretreatment step seems to be a cost-effective method of pretreatment for the enzymatic hydrolysis. Therefore, simple water soaking, and steaming was found to be an inexpensive way to recover free sugars from fruit wastes. Enzymatic hydrolysis followed by the fermentation of hydrlysate using Saccharomyces cerevisae was found to produce bioethanol from the water-steam pretreated fruit wastes. Possible mechanism of enzymatic hydrolysis has also been suggested. Effect of enzyme concentration on the hydrolysis of PAP and BP for different times at 50°C was studied. Present studies showed that fruit wastes could be exploited as a potential source of bioethanol through simple water-steam soaking followed by the hydrolysis and fermentation processes.