The orange gold: Biotechnological production of PLA/P(3HB)/limonene based polyesters from orange peel waste

Globally, vast amount of food-derived waste is generated including residues from fruit processing, which requires innovative strategies to avoid problematic disposal of useful resources. Orange peels contain a variety of valuable compounds such as limonene, enzymes, and carbohydrates that exhibit interesting properties for various applications. In this work, a biorefinery concept is presented to generate versatile bioproducts from orange peel waste. First, limonene and peroxidase enzymes were extracted from orange peels by solvent extraction and three phase partitioning, respectively. The remaining solids, containing mainly cellulose, were enzymatically hydrolyzed, and soluble monosaccharides converted into lactic acid (LA) by Weizmannia coagulans and the biopolyester polyhydroxybutyrate (P(3HB)) by Priestia megaterium. 8 g L⁻¹ limonene and peroxidases with remarkable specific activity of 426 U mg⁻¹ were extracted. Utilization of the sugars in batch fermentations resulted in a LA concentration of 17 g L⁻¹ as well as a P(3HB) content up to 43 % in cell dry weight without the need for further medium components. By combining these bioproducts, fully biobased polymer blend films of P(3HB) with PLA and limonene as plasticizer were successfully fabricated by thermoplastic processing, i.e., extrusion. In conclusion, the tested concept has shown very promising results and thereby emphasize the potential of the presented valorization strategies for orange peel waste.