Enhancing bioproduction and thermotolerance in Saccharomyces cerevisiae via cell immobilization on biochar: Application in a citrus peel waste biorefinery

Abstract

A novel method for enhancement of ethanol production and temperature tolerance of S. cerevisiae through the development of biochar-based biocatalysts (BBBs) is reported. Immobilized BBBs were applied in alcoholic fermentations of hydrolyzates generated via a citrus peel waste (CPW) biorefinery, which allowed extraction of high-purity pectin that reached 30.5% (w/w). Pistachio-nut shells, peanut shells and corks were employed for biochar generation via pyrolysis to produce the cell carriers required. All materials were highly carbonaceous with mesopore size structures (1–50 μm), while peanut shells biochar was crystalline incorporating calcite and sylvite. S. cerevisiae immobilized on pistachio-nuts biochar grown on a synthetic CPW hydrolysate, exhibited 63 g L−1 ethanol concentration and 7.9 g L−1 h−1 productivity improving substantially biosystem performance as compared to unsupported cultures. Alcoholic fermentations conducted at different elevated temperatures (37–41 °C) exhibited stable performance of the immobilized system for six repeated batch experiments. Fermentations of the CPW-hydrolyzate formed through the biorefinery at 41 °C using BBB produced 30.8 g L−1 of ethanol, while free cells achieved significantly lower concentration (13.4 g L−1). The proposed technology confers thermotolerance on S. cerevisiae, which buffers the negative impact of high temperatures on cells leading in increased bioethanol production and lower energy demand.