Valorization of Apple Pomace: Production of Phloretin Using a Bacterial Cellulose-Immobilized β-Glycosidase

In the last decade, phloretin (PHL) has attracted increasing attention due to its remarkable biological properties, including antimicrobial, antidiabetic, cardioprotective, anti-inflammatory, immunomodulatory, and antioxidant effects, becoming a leading ingredient in the cosmetic sector. In this work, an efficient, cost-effective, and highly productive biocatalytic strategy for the preparation of natural PHL has been developed starting from its glycosylated form, phloridzin, one of the main flavonoid components of apple processing waste (apple pomace). The process involved the use of the extremophilic β-glycosidase AHeGH1 immobilized on bacterial cellulose films in a two-liquid phase reaction system (water/2,2,5,5-tetramethyloxolane), allowing for the complete conversion of 5 g L^-1 of substrate in 7 h of reaction (molar conversion >99%; isolated yield 95%). Since all the materials used in the biotransformation have been recovered and recycled (i.e., solvents, aqueous phase, and catalyst), this system can be considered a zero-waste reaction. Interestingly, a further leap forward in the overall bioprocess sustainability was achieved by producing bacterial cellulose, the support for enzyme immobilization, by fermentation of apple pomace. This allows for a biocatalytic process where both the substrate and the immobilization carrier derive from the same feedstock.