Structure And Characteristics Of Gleditsia Sinensis Galactomannan And Efficient Modification Of Microaqueous System

Galactomannans are widely used in food,cosmetic,pharmaceutical,textile,paper and petroleum drilling industries due to their thickening,emulsifying,gelling and stabilizing characteristics.Galactomannans are widely distributed in nature and have attracted much attention from academia and industry due to their thickening and gelation properties in aqueous system.Gleditsia sinensis Lam.is distributed in many provinces of China and has a long planting history in China.At present,there is a lack of further research on the elucidation of the macromolecular fine structure of Gleditsia sinensis polysaccharide,the comparison of the hydrolysis characteristics of galactomannan and the modification in microaqueous systems without organic solvents,which affects the further popularization and application of Gleditsia sinensis polysaccharide.The purpose of this paper is to compare the structure and properties of Gleditsia sinensis galactomannan comprehensively and deeply,and to study the efficient modification of micro water system,so as to lay a good theoretical foundation for the popularization and application of Gleditsia sinensis galactomannan.The main findings are as follows.The physicochemical properties and structural characteristics of Gleditsia sinensis fruits were comparatively studied at different growth periods.The monosaccharide ratio(mannose/galactose)of Gleditsia sinensis galactomannan increased with its growth and development from 2.40 to 3.10.The molecular weight of Gleditsia sinensis galactomannan increased with fruit growth periods,reaching a maximum value(1.19×l06 g/mol)at 17 weeks after flowering(WAF),followed by a decrease in M,.The apparent viscosity of Gleditsia sinensis galactomannan increased gradually at their developmental stages,showing a non-Newtonian fluid characteristic of "shear thinning",while its solubility decreased gradually.Nuclear magnetic spectroscopy(NMR)studies confirmed that Gleditsia sinensis polysaccharides are typical galactomannan structures with a random distribution of galactose groups in the main chain.The hydrolysis yields and monosaccharide ratios of three galactomannans from Gleditsia sinensis,guar and fenugreek galactomannan were studied comparatively using different hydrolysis methods and analytical techniques.The content of galactose and mannose in the hydrolysates of the three galactomannans was determined by high performance liquid chromatography(HPLC)technique,and the monosaccharide yields of the one-step hydrolysis method were significantly higher than those of the twostep hydrolysis method.The monosaccharide yields of Gleditsia sinensis,guar gum and fenugreek galactomannan by two-step acid hydrolysis were 85.3%,85.4%and 87.7%respectively,while the maximum monosaccharide yields by one-step hydrolysis were 95.2%,93.5%and 93.5%respectively under the optimal hydrolysis conditions(1 M H2SO4 and 100?).Gas chromatography quantitative analysis of monosaccharide in the sample preparation process is complicated and tedious,which may affect the yield results to some extent.The structural characteristics and hydrolysis mechanism of galactomannans suggest that galactose can be released directly by acid hydrolysis,while mannose needs to be obtained by end-group hydrolysis or stepwise hydrolysis.The hydrolysis of galactomannans and the degradation behavior of standard monosaccharides suggest that galactose and mannose undergo different degrees of degradation under acid and heat conditions,and that the degradation of galactose proceeds more readily than that of mannose.The physicochemical properties and molecular weight parameters of Gleditsia sinensis,guar and fenugreek galactomannans were studied comparatively using different analytical techniques.The results showed that Gleditsia sinensis galactomannan had the highest carbohydrate content and the largest monosaccharide ratio(M/G=3.55),but its solubility was low.The intrinsic viscosity of fenugreek galactomannan was the lowest,which is attributed to the higher galactosyl substitution leading to the aggregation of the molecular chains,resulting in a more compact coil conformation.Huggins constant(K')indicated that the backbone of Gleditsia sinensis galactomannan exhibited rigid structural properties.Molecular weight parameters showed that the molecular chains of Gleditsia sinensis and guar galactomannans tend to bind to the solvent(A2>0),while the molecular chains of fenugreek galactomannans are more prone to interact with themselves(A2<0).The rheological properties of galactomannans affect their flow behavior during processing.Gleditsia sinensis,guar and fenugreek galactomannan solutions exhibited a pseudoplastic fluid behavior of "shear thinning".The viscous flow activation energy Ea was 19.42,16.71 and 16.15 KJ/mol for Gleditsia sinensis,guar and fenugreek galactomannan,respectively,indicating that the apparent viscosity of Gleditsia sinensis galactomannan solution was the most temperature dependent,followed by guar and fenugreek galactomannan.The apparent viscosities of Gleditsia sinensis,guar and fenugreek galactomannan solutions were strongly influenced by concentration,dissolution temperature and storage time.The modification of Gleditsia sinensis galactomannans by organic solvent-free microaqueous system was carried out with a carboxymethyl degree of substitution of 0.917 under optimal preparation conditions,and the reaction of sodium chloroacetate as etherifying agent was mild and less side reactions than that of chloroacetic acid.The anionic and cationic amphiphilic modified Gleditsia sinensis galactomannans were successfully prepared by the "one-pot-two-step" method with the maximum substitution of 0.136 and 0.214 for the anions and cations,respectively.the reaction of the organic solvent-free microaqueous system using a kneader was adequate,with low reagent consumption and high reaction efficiency.It was shown that the modified Gleditsia sinensis galactomannans significantly reduced their apparent viscosity and were more easily dissolved in aqueous solutions.A comparative study of Gleditsia sinensis galactomannan and its modified products and glycerol revealed that glycerol has better moisture absorption but poor moisture retention;and amphoteric modified Gleditsia sinensis galactomannan excellent moisturizing properties,indicating that it can be used as a moisturizer in the cosmetic industry.