Isolation and characterization of glucuronoarabinoxylans from wheat bran obtained by classical and ultrasound-assisted extraction methods
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Keywords
arabinoxylan, 13C-NMR, gel permeation chromatography, ultrasound, wheat bran
Abstract
Introduction Plant biopolymers like arabinoxylans possess valuable potentials as food additives with health-promoting properties or as basic products for the production of chemically functionalized polymers with unexploited technical or physiological properties. Wheat bran as an abundant milling by-product can serve as a cheap renewable source of cereal arabinoxylans. Isolation yields of xylans from plant materials are traditionally only moderate or low. Objectives A study was undertaken to investigate the effect of short-ultrasound application on the extractability of arabinoxylans from wheat bran suspended in aqueous alkaline solutions on a laboratory scale. The influence of the ultrasonic treatment on the overall extraction yield, purity and chemical structure of bran arabinoxylans under conditions of different sonication intensities and alkaline media was compared with conventional procedures not applying ultrasound. Results Extraction of xylans from bran using alkaline peroxide solutions without sonication for 240 min at 60 1C and subsequent purification provided polymers of 83% purity of a total yield of about 14%. Products of the same purity could be isolated by ultrasonication of bran suspensions in alkaline peroxide solutions for 10 min at 60 1C. Structural details of the recovered xylans were verified by high-pressure liquid chromatography-based monomer analysis, Fourier transform infrared, 13Cnuclear magnetic resonance spectroscopy and molecular weight distribution analysis by high-performance size exclusion chromatography with triple detection. Ultrasound-assisted extraction lead to a partial depolymerization of the isolated arabinoxylan. Conclusion Applying ultrasound for the extraction of xylans from plant cell walls can reduce the extraction time considerably but has no influence on the maximum extraction yield.
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