Preparation Of Xanthan Oligosaccharide By Ionic Liquid Assisted Acid Hydrolysis Of Xanthan Gum

Xanthan oligosaccharide is an oligosaccharide degraded from xanthan gum.It has good antioxidant capacity and antibacterial function,and has very good application prospects in cosmetics,pesticides and health care.However,due to the large molecular weight and complex structure,xanthan gum is difficult to be degraded into oligosaccharide molecules,which blocked the process of industrial production of xanthan gum oligosaccharides.Ionic liquids are an emerging chemically catalyzed solvent.Studies have shown that ionic liquids can assist acid degradation of cellulose.The main chain structure of xanthan gum is highly similar to cellulose.Therefore,this work uses ionic liquid to assist acid degradation of xanthan gum main chain to prepare xanthan oligosaccharide,and characterization of the physiological activity and structure of xanthan oligosaccharides.In this work,firstly,various chemical methods were used to hydrolyze xanthan gum to prepare oligosaccharides,including acid oxidation method,ionic liquid-assisted acid hydrolysis method,alkali oxidation method and ionic liquid-assisted alkali hydrolysis method.Subsequently,the reducing sugar content and hydroxyl radical scavenging ability of the oligosaccharide were compared by different methods.The results showed that the ionic liquid-assisted xanthan gum acid hydrolysis method can effectively and efficiently prepare xanthan oligosaccharides compared with other methods.The reducing sugar content of the xanthan oligosaccharide prepared by the method is 1.1 mg/m L,which is 1.7 times and 6.1times higher than that of the acid oxidation method and the alkali oxidation method,respectively,and the ionic liquid-assisted alkali hydrolysis method has a comparison with the alkali oxidation method.The decrease of reducing sugar content indicated that the imidazolium ionic liquid is not conducive to the degradation of xanthan gum under alkaline conditions.The ionic radical scavenging rate of the oligosaccharide produced by the ionic liquid-assisted acid oxidation method was 17.5%,which was 1.2 times and 16.5 times higher than that of the alkali oxidation method and the acid oxidation method,respectively.This work was followed by optimization of ionic liquid concentration,acid concentration,hydrogen peroxide concentration,reaction time,and reaction temperature for the ionic liquid-assisted xanthan gum hydrolysis method.The results showed that when the concentration of ionic liquid was 10 mg/m L,the acid concentration was 0.4 mol/L,the mass concentration of H₂O₂was 0.75%,and the temperature of 80?was the highest.The yield of xanthan oligosaccharide was 19.6%,and 2 mg/m L of xanthan oligosaccharide could remove 90%of hydroxyl radicals.Finally,this work performed physiological activity and structural characterization of oligosaccharides prepared by ionic liquid-assisted xanthan gum hydrolysis.The results of gel permeation chromatography indicated that the molecular weight of xanthan oligosaccharide was about 1500 Da and 6000 Da,respectively.The results of infrared spectroscopy indicated that the chain length of xanthan oligosaccharide was shortened and the structure of xanthan oligosaccharide backbone was similar to the xanthan.The results of nuclear magnetic resonance analysis showed that the side chain modifying group acetyl group and pyruvate group of xanthan oligosaccharide were removed,while the mannose and glucuronic acid on the side chain were not degraded.X-ray diffraction results showed that the structure of xanthan oligosaccharide is denser than the original xanthan gum,and the crystal structure was single.Physiological activity analysis showed that oligosaccharides have good antioxidant activity and antibacterial ability.The clearance of DPPH and hydroxyl radicals by 1 mg/m L oligosaccharide was 12%and 46%,respectively.Xanthan gum oligosaccharide had a semi-inhibitory concentration of 9.2 mg/m L against Xanthomonas campestris,which has good antibacterial ability.The research results of this work provided new ideas for the development of new xanthan oligosaccharides in the future.