Studies On Rheological Behaviors And Fine Structure Characterization Of Polysaccharides From Sophora Alopecuroides L. Seeds

As an important source of Chinese traditional medicine,Sophora alopecuroides L.?Leguminosae,also known as kudouzi in Mandarin?is broadly distributed in the northwest desert and semi-desert areas.It has been reported that S.alopecuroides L.comprised more than twenty types of chemical components,among which quinolizidine alkaloids predominated with various health benefits,such as anti-bacterial,anti-inflammatory,analgesic,calming,anti-carcinogenic and immunoenhanment activities.To date,however,the study of different alkaloids in S.alopecuroides L.is still an research hotspot at home and abroad.In terms of its bioactive polysaccharides,there is little information about their physicochemical properties,functional characteristics,bioactivities,fine structures and conformations in solution.In this study,therefore,crude polysaccharides?CSAP?and their neutral fraction F25from S.alopecuroides L.seeds were obtained via hot water extraction and stepwise ethanol precipitation,respectively,after which the rheological behaviors,thermal properties,solution characteristics,fine structure and molecular modeling of polysaccharides were investigated thoroughly in order to better illustrate the structure-function relationship and promote all-round development and application of polysaccharides from S.alopecuroides L.seeds.The main results were as below:?.The rheological results of steady shear tests showed that,at all concentrations and temperatures involved,CSAP solutions could assume shear-thinning behaviors,which were enhanced with increasing concentration and decreasing temperature.This was demonstrated by analyses of several fitting models,such as Williamson and Arrhenius equations.Meanwhile,there was no thixotropy observed for CSAP solutions due to non-occurrence of hysteresis loops under experimental conditions.On the other hand,the rheological results of dynamic oscillatory tests indicated the viscous behaviors of CSAP over a wide range of concentrations and temperatures,while the formation of physical gel was only detected in some cases.Besides,the CSAP solutions were found to be thermorheologically stable and simple without existence of aggregates,particles,other superstructures or energetic interactions,since their rheological behaviors were successfully applied to Time-Temperature Superposition?TTS?principle,modified Cole-Cole analysis and Cox-Merz rule.?.The thermal properties of F25 powder were fully investigated by thermogravimetry?TG?and differential scanning calorimetry?DSC?,leading to kinetic triplets for different degradation stages,e.g.,activation energy E_a of 151.79-153.45 kJ·mol^-1,pre-exponential factor A of1.34-1.89×10¹³ min^-1 and function of the most probable reaction mechanism([-ln?1-??]^1/2 as integral form,pertaining to Avrami-Eroféev A₂equation)for the major stage II.Additionally,sufficient thermal stability was revealed for F25 with relatively high integral procedural decomposition temperature?IPDT,263.31 ^oC?,comprehensive index of intrinsic thermal stability?ITS,0.42?,derivative thermogravimetry?DTG?peak temperature?T_m,304.94 ^oC?and storage life prediction,which was consistent with major enthalpic change(T_p=301.91 ^oC,?H=63.68 J·g^-1).?.The results of I₂-KI and Congo red reactions indicated that F25possessed many branches without triple-helical conformation in solution.With regard to viscometry,the intrinsic viscosity[?]of F25 was higher in deionized water(2.98 dL·g^-1)than 0.1 M NaCl(2.89-2.90 dL·g^-1)and 0.5M NaOH(2.27-2.28 dL·g^-1),signifying that different solvents could affect the inter-/intra-molecular interactions of F25 in a large extent,and then changes of molecular rearrangement,cross-linking and chain conformation in solution.Furthermore,the amorphous nature of F25 was unveiled by X-ray diffraction with higher crystallinity?25.7%?and crystallite size?7.6nm?compared to other polysaccharides.?.With the application of nuclear magnetic resonance?NMR?technique and molecular modeling,the fine structure of F25 was further confirmed as a galactomannan with 1,4-linked?-D-Manp backbone distributed randomly?M/G=1.48-1.84?by major T-?-D-Galp?86.82%?and/or minor 1,4-linked?-D-Galp?13.18%?at O-6.Its 2D and 3D schematic structure were exhibited as follow:...