Feruloyl esterase-catalysed synthesis of glycerol sinapate using ionic liquids mixtures

The ability of a feruloyl esterase (AnFaeA), either in free or immobilised (cross-linked enzyme aggregates) form, to catalyse the esterification of glycerol, a major by-product of the biodiesel industry, with sinapic acid was studied in four hexafluorophosphate anion-containing ionic liquids: ([Bmim][PF6], [Omim][PF6], [C2OHmim][PF6] and [C5O2mim][PF6]). Such ionic liquids are considered ‘green’ reaction systems. The synthetic reaction was optimised in [C2OHmim][PF6] and the highest conversion yield was 72.5 ± 2.1%, while, at the same reaction conditions in [C5O2mim] [PF6], a similar conversion yield was obtained (76.7 ± 1.5%). AnFaeA was active in its free and immobilised form, with the latter retaining a part of its synthetic activity after 5 consecutive 24 h-period reaction cycles. Sinapic acid was esterified to one of the primary hydroxyl groups of glycerol and retained, after esterification, 63.1 ± 0.3% and 89.5 ± 1.1% of its antioxidant activity against low-density lipoprotein oxidation, when added at concentrations of 10 and 60 μM, respectively, in the assay mixture.