Enzymic production of a feruloylated oligosaccharide with antioxidant activity from wheat flour arabinoxylan

Summary.

Background: Main cereals such as rice, wheat, barley, and corn belong to the family Gramineae and have similar cell-wall composition. Since cereal cell walls are a good source of dietary fibre, meeting one-half of the daily requirement of 30 g of dietary fibre can be achieved by the regular consumption of cereals. Many studies have dealt with the isolation of feruloylated oligosaccharides from Gramineae by treatment with polysaccharide hydrolysing enzymes. Aim of this study: Therefore, the purpose of this study was to investigate the production of feruloylated oligosaccharides from insoluble wheat flour arabinoxylan (WFAX) by treatment with a Thermoascus aurantiacus family 10 endoxylanase (XYLI) and the evaluation of their antioxidant activity. Methods: The main feruloylated oligosaccharide was purified by anion-exchange and size-exclusion chromatography (SEC). Alkaline saponification and acid hydrolysis were used for product identification. Evaluation of antioxidant activity was performed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) reduction assay and the inhibition of copper-mediated oxidation of low density lipoprotein (LDL). Results: The optimal conditions for WFAX hydrolysis using the XYLI have been determined to be 100 U g⁻¹ of WFAX for 30 min at 50 °C. Saponification of the oligosaccharide released FA and oligosaccharide. The released oligosaccharide consisted of arabinose and xylose in a molar ratio of 1:3 and these results support the identity of the feruloylated oligosaccharide as feruloyl arabinoxylotrisaccharide (FAX₃). FAX₃ showed profound antioxidant activity in 2,2-diphenyl-1-picrylhydrazyl (DPPH) reduction assay exhibiting an antiradical efficiency of 0.035 (× 10⁻³) and inhibited the copper-mediated oxidation of human low density lipoprotein (LDL) in a dose-dependent manner with almost complete inhibition at 32 μM. Conclusion: A feruloylated oligosaccharide (FAX3) was isolated from WFAX after enzymatic treatment with XYLI. We verified antioxidant activity of FAX₃ which may be important in preventing or reducing the progression of atherosclerosis by inhibiting the peroxidation of lipoproteins.