Studies On The Molecular Strutures And Physicochemical Properties Of Polysaccharides Extracted From Hulless Barley

Hulless barley(Hordeum vulgare Linn.var.nudum Hook.f.)is the staple food of Tibetan people,and mainly produced from Tibet,Qinghai,Sichuan,Yunnan and other places of China.It has high nutritional values and versatile health benefits,which can be at least partly associated with its abundant dietary fibers.However,the main polysaccharides in its dietary fibers have not been intensively studied.Therefore,this study aimed to separate and purify polysaccharides from hulless barley,and to intensively investigate their molecular structures and physicochemical properties.The water-and alkaline-soluble bran polysaccharides(WSBP and ASBP)were separated from the bran of hulless barley,and then sequentially purified via DE-32 and S-400 column chromatography.The purity of WSBP and ASBP was higher than 98.0%.Next,their molecular structures were determined.The molecular weight(MW)of WSBP and ASBP was 5.0 ×103 Da and 2.8 × 105 Da,respectively.Monosaccharide composition analysis found that the WSBP was mainly composed of glucose,with a small amount of arabinose and xylose,which,on the contrary,were the main sugars found in the ASBP.In addition,the methylation analysis suggested that 1-linked glucopyranosyl(Glcp)and 1,4-linked glucopyranosyl(Glcp)were the main residues of the WSBP after methylation,while 1,2,3,5-linked arabinofuranosyl(Araf)and 1,2,3,4-linked xylopyranosyl(Xylp)were the main residues of the ASBP after methylation.Finally,their physicochemical properties were investigated.The viscosity of WSBP(<3.0%,w/v)was very low and showed the properties of Newtonian fluid,while the ASBP had higher viscosity than the WSBP at the same concentration.Especially,when the concentration of ASBP was 2.0% and3.0%,it had a weak shear thinning tendency,indicating the properties of pseudoplastic fluid.On the other hand,the observation under scanning electron microscopy(SEM)found that the WSBP exhibited a simple morphology likes broken fragments or sheets,while the ASBP was diverse and complex in morphology.In conclusion,it is of great difference about the molecular structures and physicochemical properties of the WSBP and ASBP in hulless barley.Clarifying and comparing the characteristics of its water-and alkalinesoluble polysaccharides can provide a chemical basis for its health benefits,and also provide a reference for its further utilization.