Valorisation of Verge-Stage Pawpaw Fruit to Enhance Bamboo Juice Hydrolysis and Fermentation for Bioethanol Production

Abstract

Objective This study investigated bioethanol production from fermented bamboo juice enhanced with verge-stage Carica papaya (pawpaw), where amylase and invertase hydrolyse starch and sucrose into fermentable sugars, improving substrate availability and fermentation efficiency. Methods A randomized experimental design was used to evaluate the effect of varying verge-stage pawpaw concentrations (10-40 g/L) on bamboo juice fermentation and bioethanol production. Bamboo juice was collected from bamboo plantations using traditional tapping device locally known as “mbeta” and fermented under room temperature conditions to minimize variability during fermentation. To enhance hydrolysis and improve fermentation efficiency, pawpaw fruit at the verge-stage was added to the fermenting juice. After fermentation, the mixture was distilled at a controlled temperature of 78 °C. Results Total soluble solids declined from 9.5±0.03 to 2.63 ± 0.02 °Brix over 312 hours with pawpaw fruit, producing the percentage alcohol by volume of 6.56% compared to 9.3±0.01 to 3.1±0.03 °Brix, achieving the percentage alcohol by volume of 5.25% without pawpaw fruit after 11 days before distillation. Bamboo juice was fermented by microbes identified as yeast and moulds which efficiently convert sugars into bioethanol under experimental conditions. Fermented bamboo juice broth with pawpaw fruit produced 33% v/v bioethanol, followed by the one without pawpaw fruit, yielding 30% v/v after distillation. The produced bioethanol was blended to 30% and re-distilled to achieve 80% purity, making it suitable for use as a biofuel. Conclusion Findings demonstrate that the amylase and invertase enzymes present in pawpaw fruit are effective in enhancing fermentation process. The study provides new insights into the potential use of bamboo juice feedstock and natural enzyme supplementation to improve bioethanol production efficiency and yield, supporting cost-effective and sustainable biofuel production. Bamboo juice emerges as a sustainable resource for boosting bioethanol output, contributing to the transition toward cleaner energy and reducing dependence on fossil fuels.