Integrated biorefinery scheme for apple pomace: Synergistic extraction and fermentation for dual recovery of pectin and 2,3-butanediol

Abstract

This study presents an integrated, solvent-free biorefinery approach that couples microwave-assisted extraction (MAE), ultrafiltration (UF), and separate enzymatic hydrolysis and fermentation (SHF) to co-produce pectin- derived oligosaccharides (POS), predominantly oligogalacturonides (OGalA), and 2,3-butanediol (2,3-BDO) from apple pomace (AP). Through response surface methodology, optimized MAE temperature and time conditions to maximize OGalA formation were identified, while also limiting sugar degradation. Under these conditions (136 ◦C, 8.1 min), the extract contained OGalA at 4.0 ± 0.2 g/L, corresponding to a recovery of 53.7 ± 0.8%, and a pectin yield of 22.3 ± 0.2% was achieved (dry AP basis). Subsequently, an ultrafiltration step using a 3 kDa membrane yielded an OGalA solution concentrated to 11.5 ± 0.1 g/L and partially depleted small molecules. Compositional profiling also confirmed a notable enrichment of the rest of the oligosaccharide fractions, with increases ranging from 2.4- to 3.2-fold. In parallel, the MAE-pretreated solid, selectively depleted in pectic do- mains and enriched in glucan (~37%), was saccharified and fermented via a sequential hydrolysis-fermentation scheme to produce 2,3-BDO. Fermentation trials with Bacillus strains achieved concentrations of 10.3 ± 0.4 g/L (B. amyloliquefaciens) and 9.5 ± 0.2 g/L within 47 h (B. licheniformis), with sugar clearance below 48 h at 10–15% (w/v) solids loading. In conclusion, an integrated MAE → UF → SHF configuration co-producing POS and 2,3-BDO offers a practical route to valorize AP and advance circular bioeconomy goals in fruit-processing regions.