Natural Nutrient Supplements and Sisal Bole Yeast Isolate: A Synergistic Approach to Bioethanol Production from Sisal Bole Juice

Abstract The increasing demand for sustainable biofuels and the need to reduce reliance on synthetic nutrients additives during yeast fermentation has prompted the search for cost effective and locally available nutrients sources. This study investigated the potential of natural nutrients supplements derived from agro-waste (orange, cassava and banana peels) as well as sisal bole yeast isolates to enhance bioethanol production from sisal bole juice. Yeast colonies were isolated from the sisal bole juice and then characterized morphologically, biochemically and through molecular identification using PCR amplification of the ITS1 and ITS4 rDNA regions. A 2n full factorial design was employed to study the effect of natural nutrient supplements combination and dosage on the bioethanol yield. Macroscopic results revealed that the isolated colonies were either ellipsoidal or oval and gram-positive similar to Saccharomyces cerevisiae. Sequencing of the PCR products confirmed that all positive isolates showed high similarity (>99%) to Saccharomyces cerevisiae. The highest bioethanol yield achieved was 27.38% w/w with orange peels (3 g/100 ml), cassava peels (3 g/100 ml) and banana peels (1 g/100 ml) compared to 20.13% w/w for the blank and 18.71% w/w for the control. Statistical analysis confirmed a significant linear model, with notable effects from orange peels and interactions between orange and banana peels. These findings highlight the potential of natural supplements to replace expensive and less accessible artificial supplements such as Magnesium sulfate heptahydrate, Iron (II) sulfate tetrahydrate and Copper (II) sulfate pentahydrate which provide essential Mg, Fe and Cu that improved bioethanol production efficiency.