Optimization of a Green Extraction/Inclusion Complex Formation Process to Recover Antioxidant Polyphenols from Oak Acorn Husks (Quercus Robur) Using Aqueous 2-Hydroxypropyl–Cyclodextrin/Glycerol Mixtures

Aqueous mixtures of glycerol and 2-hydroxypropyl-β-cyclodextrin (CD), two non-toxic eco-friendly substances, were used as a means of extracting antioxidant polyphenols from oak acorn (Quercur robur) husks. The process was optimized by implementing a central composite (Box-Behnken) experimental design and response surface methodology, taking into consideration the critical parameters (independent variables) of glycerol concentration (Cgl), CD concentration (CCD) and temperature (T). The assessment of the extraction model was based on three responses: the total polyphenol yield (YTP), the antiradical activity (AAR) and the reducing power (PR). The model illustrated that YTP depended significantly on Cgl and CCD, but not on T, whereas both antioxidant properties considered (AAR and PR) were temperature-dependent. The maximum predicted YTP was 122.19 mg GAE per g dry husk weight, while the extract obtained under optimized conditions displayed strong antioxidant activity.