High efficiency production of ferulic acid using feruloyl esterase and xylanase in deep eutectic solvents

Ferulic acid is a natural phenolic chemical which is widely present in plants and widely used in food and cosmetic industries. It is used as the cross-linking agent for the preparation of edible films and as skin protection agents. Enzymatic hydrolysis of lignocellulose to produce ferulic acid has been studied for many years and is rarely used in industry due to easy deactivation of enzymes. A deep eutectic solvent (DES) is exploited as a novel co-solvent for improving the activity and stability of enzymes. A mixed enzyme system composed of feruloyl esterase and xylanase was constructed for catalytic degradation of de-starched wheat bran (DSWB) to produce ferulic acid. When the ratio of feruloyl esterase-to-xylanase reached 1 : 1, the release of ferulic acid reached a maximum. Four DESs were synthesized and the effects of compositions and concentrations on the release of ferulic acid from DSWB were evaluated. The mixed enzymatic system showed the best performance in the ChCl-Gly DES aqueous solution (a volume ratio of 1 : 2). Through the determination of the enzymatic properties and catalytic conditions, the mixed enzymatic system was applied to the catalytic reaction. A ferulic acid yield of 4.2 mg g-1 DSWB was obtained under the optimum conditions. The results suggested that efficient production of ferulic acid from lignocellulosic biomass can be realized through the synergistic effects of feruloyl esterase and xylanase in DES aqueous solution. The mixed enzymatic system showed the best performance in the ChCl-Gly DES aqueous solution (a volume ratio of 1 : 2).