A Study on the Optimization of Pretreatment Parameters for Pineapple and Mango Peel Waste to Enhance Ethanol Production

Abstract

Lignocellulosic biomass represents a promising renewable substrate for sustainable bioethanol production without competing with food or feed resources. Fruit wastes, being cheap and abundantly available, offer significant potential in this context. In the present study, pineapple and mango peels were evaluated for their suitability in bioethanol production due to their appreciable amounts of simple and complex sugars. However, their low fermentable sugar content and high fiber levels necessitated pretreatment to improve sugar release. Both physical and chemical pretreatments were applied to enhance hydrolysis efficiency. Hydrothermal pretreatment using water at different temperatures indicated that sugar release increased significantly with temperature, achieving maximum reducing sugar concentrations at 100°C, with pineapple peel yielding 23.57 g L⁻¹ and mango peel 19.35 g L⁻¹ after 8 h. Beyond this period, no significant increase was observed, confirming 8 h as the optimum incubation time. Alkaline pretreatment with NaOH enhanced delignification, cellulose swelling, and partial decrystallization, yielding maximum reducing sugar concentrations of 27.67 g L⁻¹ (pineapple) and 22.24 g L⁻¹ (mango) at 1.5% NaOH. Acid pretreatment with H2SO4 further improved sugar recovery, with maximum yields of 33.17 g L⁻¹ (pineapple) and 26.42 g L⁻¹ (mango) at 1.0% acid concentration, beyond which no significant increase was observed. The results demonstrate that both hydrothermal and chemical pretreatments substantially enhance the release of fermentable sugars from fruit wastes, with acid pretreatment showing the highest efficiency. These findings highlight pineapple and mango peels as effective feedstocks for bioethanol production, while also offering an ecofriendly approach for waste utilization and sustainable energy generation.