Synthesis of antioxidants with free and immobilised fungal feruloyl esterases

Feruloyl esterases (FAEs, E.C. 3.1.1.73, CAZy family CE1) are enzymes that are secreted by a wide range of fungi and bacteria as part of the enzymes hydrolysing plant biomass. Under conditions of low water content, FAEs can also carry out (trans)esterification reactions. Thus, their potential use as biocatalysts for the production of antioxidants with applications in food, cosmetic and pharmaceutical industries has been investigated in recent years. We characterised the biosynthetic potential of four new FAE enzymes from a thermophilic fungus. We focused on optimizing reaction conditions for the synthesis of ferulate esters with improved hydrophobic or hydrophilic properties; prenyl ferulate and 5-O-(trans-feruloyl)-arabinofuranose, respectively. In addition to using free enzymes, we also immobilised them on the mesoporous silica material SBA-15 with pore sizes ranging from 7 to 10 nm, to improve the esterification-to-hydrolysis ratio of the enzymes. It has been shown previously that immobilisation renders enzymes more resilient to adverse conditions and increases their productive life time [1]. Furthermore, immobilisation may also result in a decrease of unwanted side reactions (hydrolysis of transesterification) [2]. In agreement with that, we achieved a higher product yield with immobilised enzymes compared to free enzymes. The immobilised biocatalysts are also more easily re-usable for several production cycles, thus lowering production costs