Upcycling extraction residues from fruit waste bioactive compound recovery via fermentative and photofermentative hydrogen production

This study investigates the valorization of orange peel herbal dust (OPHD) and black elderberry press cake (BEPC), by-products of the food industry, through an integrated biorefinery approach. The process involved two main steps: the recovery of phenolic compounds using ultrasonic-assisted extraction and the subsequent production of hydrogen via dark fermentation (DF) and photofermentation (PF). Experimental results demonstrated that it is possible to efficiently recover phenolic compound (Extraction Yield = 22.33 ± 0.92 %, Total Phenolic Content = 24.08 ± 1.16 mg gallic acid/g dry weight from OPHD; Extraction Yield = 17.80 ± 0.41 %, Total Phenolic Content = 32.83 ± 2.24 mg gallic acid/g dry weight from BEPC) and that the extraction residues can be further valorized via biological routes. More specifically, OPHD exhibited hydrogen yields of 150.3 mL H₂/g VS and 218.0 mL H₂/g VS in DF and sequential DF-PF, respectively. A lower DF yield (20.5 mL H₂/g VS) was obtained from BEPC, which provided better performance in single-stage PF. These findings contribute to advancing sustainable waste management practices and enhancing the economic viability of biorefinery processes in the food industry.