Optimization of feruloyl esterase-catalyzed synthesis of feruloylated oligosaccharides by response surface methodology

The feruloyl esterase expressed in Depol 740L from Humicola spp. exhibited esterifying activity for the feruloylation of selected di- and oligosaccharides in a surfactant-less microemulsion medium composed of n-hexane, 2-butanone and MES–NaOH buffer (51:46:3, v/v/v). As compared to their corresponding ferulic acid, the feruloylated di- and oligosaccharides demonstrated similar or higher potential radical scavenging properties. By varying the media composition, the highest bioconversion yields were obtained in the n-hexane, 2-butanone and MES–NaOH buffer mixture using arabinobiose (8%), xylobiose (9%) and raffinose (11%) as substrates. However, using galactobiose as substrate, the highest bioconversion yield (27%) was obtained in the n-hexane, 1,4-dioxane and MES–NaOH buffer mixture. The chemical structure of the feruloylated di- and oligosaccharides was confirmed by APCI-MS. Response surface methodology, based on a 5-level and 4-factor central composite rotatable design revealed that enzyme amount and substrate molar ratio were the most important variables for the bioconversion yield of feruloylated raffinose.