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

Aqueous mixtures of glycerol and 2-hydroxypropyl-beta-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 (C-gl), CD concentration (C-CD) and temperature (T). The assessment of the extraction model was based on three responses: the total polyphenol yield (Y-TP), the antiradical activity (A(AR)) and the reducing power (P-R). The model illustrated that Y-TP depended significantly on C-gl and C-CD, but not on T, whereas both antioxidant properties considered (A(AR) and P-R) were temperature-dependent. The maximum predicted Y-TP was 122.19 mg GAE per g dry husk weight, while the extract obtained under optimized conditions displayed strong antioxidant activity.