An integrated SSF strategy enables superior valorization of apple pomace into 2,3-butanediol using Paenibacillus polymyxa

The valorization of agro-industrial residues is fundamental to developing a sustainable circular bioeconomy. This study establishes a robust framework for converting apple pomace, an abundant lignocellulosic waste, into the high-value platform chemical 2,3-butanediol (2,3-BDO) using the non-pathogenic bacterium Paenibacillus polymyxa . A comprehensive optimization was conducted through the systematic comparison of Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF) strategies. Key process parameters, including hydrothermal pretreatment conditions (time and solids loading) and synergistic enzyme loading, were optimized for each configuration. Although the optimized SHF process yielded a higher product concentration (24.2 g/L at 16 % solids), the integrated SSF configuration (21.0 g/L at 11 % solids) demonstrated superior overall process efficiency, yielding 238 kg of 2,3-BDO per ton of dry apple pomace versus 189 kg for SHF. Further optimization of enzyme loading in the SSF process enhanced this yield to 268 kg/ton. To maximize productivity, a fed-batch strategy was implemented for the optimal SSF configuration, which culminated in a final concentration of 32.7 g/L. This corresponded to an overall mass yield of 371 kg of 2,3-BDO per ton of pomace. This work, to our knowledge, represents the first comprehensive optimization of 2,3-BDO production from apple pomace using P. polymyxa . It is concluded that the integrated SSF process, despite achieving lower batch titers, represents a more promising route for industrial application due to its operational simplicity and higher material conversion efficiency. These findings provide a critical foundation for advancing circular biorefinery models based on fruit waste.