A modular biocatalyzed flow preparation of olive oil phenols tyrosol acetate, hydroxytyrosol and hydroxytyrosol acetate

Tyrosol (Ty) and hydroxytyrosol (HTy) are valuable phenolic constituents of olive oil endowed with a range of biological activities, including antioxidant capacity and antimicrobial effects.[1] The availability of green methodology for the sustainable production of Ty acetate, HTy and HTy acetate is highly appealing for food, nutraceutical and cosmetic applications. In this context, we designed an efficient biocatalyzed protocol for the transformation of Ty into HTy and for the obtainment of their acetyl metabolites. Two different biocatalysts were employed in a continuous flow system (Scheme 1). The first step was the oxidation of Ty by a free tyrosinase from Agaricus bisporus in presence of oxygen and ascorbic acid, to avoid over-oxidation of the product. The aqueous flow stream was then extracted in-line with ethyl acetate to recirculate the aqueous layer containing the biocatalyst and the excess of ascorbic acid to improve the economy of the protocol in a self-sufficient closed-loop system. The organic phase was purified in-line thanks to a catch and release procedure using supported boronic acid to trap HTy, leaving unreacted Ty in solution. To obtain the acetyl metabolites, a bioreactor packed with an immobilised acyltransferase from Mycobacterium smegmatis (MsAcT) was used.[2] Thanks to this modular set up, HTy was obtained with an isolated yield of 75%, whereas the acetyl metabolites showed yields up to 80% in 10 minutes.