The Self-Assembly,Structure-Property Relationship And Application Of Tamarind Xyloglucan

Xyloglucan polysaccharides comprise the main hemicellulose group of primary cell walls in dicotyledonous plants,but the difficulty of purification and the low molecular weight hindered their industrial utilization.Xyloglucan derived from Tamarind seed（Tamarind xyloglucan,XG）is the only resource of xyloglucan which is commercially available and thus most extensively studied.XG is endowed with unique rheological properties and distinguished ability to form gels.It also has unique self-assembly behavior and versatile applications.To deeply understand its structure-property relationship and self-assembly characteristics,XG was studied from several aspects and the main findings are as follows:（1）Tamarind kernel powder（TKP）was composed of 64.9%polysaccharide（galactose:xylose:glucose 1:1.39:2.58）,17.5%protein and 6.8%fat.XG was extracted from TKP at three different temperatures in deionized water.The morphology,structure and properties of the three XGs（XG30,XG55and XG80）were significantly different.Their radii of gyration（Rg）were 23.2 nm,59.6 nm and 72.5 nm,respectively.XG extracted at higher temperature has less branches and higher molecular weight（8.759×10⁵）,exhibiting higher apparent viscosity and distinguished ability to form gels.（2）The gel strength of TKP（1%）-ethanol gel increased rapidly in the range of 13%-15%ethanol volume fraction（from 141 Bloom g to 982 Bloom g）.It was observed that the defatted TKP-ethanol gel was heterogeneous under optical microscope,showing many regular hexagonal structures.The honeycomb-like structure of XG80-ethanol gel was observed under scanning electron microscope（SEM）.By atomic force microscopy（AFM）,the significant cross-linking trend of purified XG80 was observed at a very sparse concentration（5 ug/mL）,indicating XG’s excellent gelling capacity.The dynamic formation process of XG’s special fern morphology and its interesting fine structure of external spines and inner branches were observed by fluorescence microscopy.（3）Degalactosylation of XG with galactose removal rate of 33.3%,38.9%,41.5%and 43.1%induced drastic self-assembly transition of modified xyloglucan（mXG）from spherical aggregates toward ribbon-like aggregates,and it led to largely decreased water solubility（from 80.6%to 13.4%）and decreased consistency coefficient(from 2248 to 34 mPa·s^0.9).To better understand this phenomenon,the size of the ellipsoid-like aggregated nanoparticles were carefully measured and compared,and it was found out that those nanoparticles which lost more galactose residues turned out to be more slender and tend to bind and stack closely in parallel,thereby forming huge ribbon-like aggregates.The galactose residue is considered as the hydrophilic group,and the decreased number of which caused a more hydrophobic behavior.（4）XG has excellent soil aggregation promoting effect and excellent film forming property.Sprayable XG-based liquid films for agricultural use were prepared by blending TKP with glycerol the plasticizer,polyvinyl alcohol the binder and carbonized seed coat powder.The addition of glycerol increased the water vapor permeability（WVP）of the liquid film,and the WVP of the eight liquid films ranged from 0.52-1.92 g·mm m^-2 h^-1 kPa^-1.The addition of XG in the mix can reduce the soil moisture evaporation by half.SEM characterization showed that XG effectively promoted soil/sand aggregation.In addition,temperature-responsive mXG was prepared by enzymatic hydrolysis modification,which could quickly self-assemble into gel liquid film on the soil surface at room temperature.