Hybrid cellulose-poly(4-vinylpyridine) adsorbents produced via ATRP and their application to target polyphenols in winemaking, olive oil production and almond processing residues

Hybrid cellulose-poly(4-vinylpyridine) particles (MCC-P(4VP)) were synthesized via ATRP grafting and used as adsorbents to target polyphenols in residues derived from winemaking, olive oil production and almond processing. These hybrid particles preserve good conditions to be used in continuous sorption/desorption processes and were assessed for the retention of polyphenols in solvent mixtures ranging from 0 to 100% water content. Other seven adsorbents were used in these assays, including three commercial resins and further materials synthesized in this research with 4VP. We show that the 4VP based adsorbents present a much higher average polyphenol retention in a broad range of working conditions, namely concerning the water content of the extract. This behavior stems from the strong binding capacity of the pyridyl functional group towards many polyphenols and excels with MCC-P(4VP) adsorbents when the hydrophobic interactions play a minor role. MCC-P(4VP) adsorbents were also used for purification and fractionation of polyphenols using simple sorption/desorption steps. A fraction enriched with the malvidin - 3-O-glucoside anthocyanin was obtained from grape pomace. Fractions with high content of isorhamnetin-3-O-rutinoside were isolated from almond. Fractions enriched in secoiridoids and flavonoids were produced from olive mill wastewater while many phenolic alcohols and acids were removed. These results show the potential of the MCC-P(4VP) adsorbents to improve downstream processing of polyphenols and increase the biorefining efficiency, namely through the direct handling of organic extracts at high polyphenol concentration. This research also has disclosed the formation of a polymer population deviating from the expected homogeneous process in ATRP grafting. The partition of ATRP reactants between two regions in the homogeneous phase could be a source of some potentially interesting issues relevant to monomers presenting strong H-bond capability, such as 4VP. Thus, many future developments are possible for the designing of the functional materials here addressed, including the introduction of molecular recognition features.