Valorization of Apple pomace: production of phloretin using a bacterial cellulose-immobilized beta-glycosidase

Food industries produce around 4 million metric tons of apple pomace every year , which is a mixture of residues and byproducts from apple processing. A high abundance of valuable phenolic compounds is still present in apple residues, making them a cheap natural source of bioactive molecules for applications in the pharmaceutical, cosmetic, and food sectors. Among these compounds, phloretin is drawing particular attention for its biological properties, including antimicrobial, anti-inflammatory, immunomodulatory, and anti-aging effects. However, the small amount of phloretin present in the biomass in comparison to its glycoside, phloridzin, contributes to the preference for using the latter as the starting material. Apple pomace also contains a high quantity of sugars, making it suitable as feedstock for bacterial cultivation. Our group used it to grow Komagataeibacter xylinus DSM2325, an acetic acid bacterium able to produce bacterial cellulose (BC), a natural polymer with high crystallinity and purity. Through simple chemical modifications, we transformed BC into a promising support for the covalent immobilization of the extremophilic β-glycosidase from Alicyclobacillus herbarius (AheGH1)7. This biocatalyst has been employed in a biphasic system (HEPES buffer:TMO 50:50, 20 mg/mL imm-AHeGH1, 2 mg/gmatrix enzyme loading) resulting in complete de-glycosylation of 5g/L phloridzin within 7 hours. While the enzyme immobilization onto BC cellulose pellicles allowed for high catalyst stabilization and its recovery and reuse (>7 cycles), the employment of the unconventional green solvent TMO dramatically facilitated the isolation of the desired product (i.e., 95% of yield), leaving the sugar moieties in the water phase for their potential reutilization.