Cell wall hydroxycinnamates in wild rice (Zizania aquatica L.) insoluble dietary fibre

The contents of ester-linked phenolic acids in wild rice (Zizania aquatica L.) dietary fibre were quantified by HPLC analysis, and oligosaccharide hydroxycinnamates were isolated and identified to investigate the linkages of hydroxycinnamic acids to cell wall polymers. In wild rice insoluble dietary fibre (WRIDF), ferulic acid was the most abundant phenolic acid (3942 mug g(-1)), but significant amounts of sinapic acid (518 mug g(-1)) and p-coumaric acid (142 mug g(-1)) were also detected. Treatment of WRIDF with carbohydrate hydrolases or trifluoroacetic acid released several oligosaccharide hydroxycinnamates. After fractionation with Amberlite XAD-2, five feruloylated oligosaccharides were isolated by gel chromatography and semi-preparative HPLC and identified as arabinoxylan ferulate fragments. The feruloylated tetrasaccharide {[5-O-(trans-feruloyl)][O-beta-D-Xylp-(1-->2)]-O-alpha-L-Araf-(1-->3)}-O-beta-D-Xylp-(1-->4)-D-Xylp was isolated for the first time from edible plant material. Although some results indicated that sinapic acid is also (at least partially) linked through an ester bond to polysaccharides, isolation of defined oligosaccharide sinapates was not achieved.