New immobilized lipases for synthesis of tyrosol esters in hydrophobic deep eutectic solvents

As a new generation of water-immiscible solvents, hydrophobic deep eutectic solvents (HDESs) have shown great potential as green and sustainable reaction media for biocatalytic applications. Tyrosol is a major phenolic compound present in olive oil and wine with potential pharmacological benefits due to its strong antioxidant properties, and its application can be highly extended by increasing its lipophilicity through esterification. In this study, two lipases, one from Aspergillus oryzae (AOL) and another from Pseudomonas fluorescens (PFL), were immobilized on inorganic salt crystals (i.e. @Cu3(PO4)2) and on metal-organic frameworks (i.e. @HKUST-1). The structural features of these four new biocatalysts were characterized and their activity and stability assayed. They were successfully employed to catalyze the esterification of tyrosol to produce tyrosol esters in HDESs with excellent yields, which are comparable to, or even better than, the results obtained by using the most commonly used commercial lipase (i.e. Novozym 435 from Novozymes). The carboxylic acid-based HDESs provide not only a reaction medium but also an acylating agent for the enzymatic (trans)esterification reactions.