Bioconversion of spent passion fruit rind to ethanol: Integrating hemicellulose hydrolysis and detoxification

Effective fermentation of the hemicellulosic fraction, which constitutes approximately one-third of lignocellulosic biomass, is essential for the advancing of second-generation bioethanol production. This study optimizes the dilute sulfuric acid pretreatment by response surface methodology (RSM) to increase xylose release and minimize fermentation inhibitors from spent passion fruit rind (SPFR) residue. The optimized parameters (114 °C, 9.8 min, and 0.2 M H₂SO₄) yielded a xylose concentration of 121.8 mg/g db, accompanied by 2.3 mg/g db furfural production. Detoxification with overliming (Ca(OH)₂, pH 11) further reduced inhibitory chemicals by 12–23 %, improving fermentative compatibility. Subsequent fermentation of detoxified hydrolysate using Pichia (Scheffersomyces) stipitis produced an ethanol concentration of 9.7 g/L, achieving a yield of 0.42 g/g. The batch fermentation of SPFR-derived xylose rich hydrolysate demonstrates effective bioethanol production from the hemicellulosic fraction, supporting its potential use in second-generation bioethanol.