Mild Pretreatment Combined with Fed-Batch Strategy to Improve the Enzymatic Efficiency of Apple Pomace at High-Solids Content

This a two-part study was conducted to improve the enzymatic saccharification of apple pomace (AP) by pretreatment and fed-batch enzymatic hydrolysis. The impact on the enzymatic hydrolysis and structural characterization in AP of four pretreatment processes, sodium hydroxide (SH), ethanol (ETH), liquid hot water (LHW), and Phanerochaete chrysosporium (PC), were evaluated. In addition, the enzymatic hydrolysis efficiency of AP at high solids content was improved by optimizing the enzyme hydrolysis conditions and using fed-batch strategy. The results demonstrated that both ETH 160 °C and PC pretreatments effectively enhanced the efficiency of enzymatic saccharification in AP while disrupting its compact structure. Notably, PC solid-state fermentation for 7 d proved to be a mild yet effective pretreatment method for AP. By utilizing PC pretreated residue at a substrate content of 20% (w/v) with an addition of 5 mg/g pectinase and 50 mg/g Tween 80, along with employing fed-batch enzymatic hydrolysis, the total sugar concentration increased by 30.3% after 72 h. At this point, the highest total sugar concentration reached 77.5 g/L with an enzymatic hydrolysis yield reaching 73% (glucose). This study presents not only the first application of PC as a pretreatment method for AP but also establishes a new enzymatic process with high solids content to provide a new strategy for AP resource utilization.