ISOLATION AND PARTIAL CHARACTERIZATION OF FERULOYLATED OLIGOSACCHARIDES FROM MAIZE BRAN

摘要

Maize bran contains phenolic acids [similar to 4% dry matter; mainly ferulic acid (Fe) and also diferulic acid], heteroxylans (similar to 50%), and cellulose (similar to 20%), but is devoid of lignin. Treatment of maize pericarp with 0.05 M trifluoroacetic acid at 100 degrees C for 2 h released similar to 90% of the heteroxylans and similar to 90% of the ferulic acid and its esters. After fractionation of the products with Amberlite XAD-2 and Sephadex LH-20 three main feruloylated oligosaccharides (F-3-F-7) were isolated. They represented similar to 30% of the ferulic acid, and similar to 2% of the neutral sugars contained in the hydrolysis supernatant. The compositions of F-7, F-6, and F-3 were Fe-Ara (1:1), Fe-Ara-Xyl (1:1:1), and Fe-Ara-Xyl-Gal (1:1:1:1), respectively. The structures of the three oligomers were determined using chemical methods (methylation, acetalation, reduction) and C-13 NMR spectroscopy: F-7 was 5-O-(trans-feruloyl)-L-Araf; F-6 was O-beta-D-Xylp-(1 --> 2)-[5-O-(trans-feruloyl)L-Araf]; and F-3 was O-L-Galp-(1 --> 4)-O-D-Xylp-(1 --> 2)-[5-O-(trans-feruloyl)-L-Araf]. F-7 has been previously isolated from other monocots especially from wheat bran and soluble arabinoxylans from wheat flour; this is the first report of feruloylated oligosaccharides F-6 and F-3. Our results suggest that these oligomers are side-chain constituents of heteroxylans in maize bran. Ferulic acid is probably partly responsible for the insolubility of heteroxylans by coupling polysaccharide chains through ferulic acid dimers. [References: 30]