The Research Of The Influence Of Three Extraction Methods On The Structural,Rheological And Emulsifying Characterization Of Pectins From Gardenia Jasminoides Var. Fortuniana

Gardenia jasminoides var.fortuniana has been widely cultivated as an important garden plant in China.The utilization of Gardenia jasminoides var.fortuniana has not been paid much attention except for a small amount of ornament and food.Gardenia jasminoides var.fortuniana has been found to contain a large number of active components and pectin polysaccharides.In this paper,the structure,rheology and emulsification properties of pectins were studied by three extraction methods with Gardenia jasminoides var.fortuniana as raw material.The experimental results are as follows:1.The pectin of Gardenia jasminoides var.fortuniana was extracted with citric acid,sodium hydroxide and water,named ACP,ALP and HWP,respectively.The structural differences among ACP,ALP and HWP were studied by measuring the relative molecular weight,chemical composition,microstructure and X-ray diffraction.The results showed that ACP had the highest relative molecular weight（579 KDa）,the highest neutral sugar content（59.33 mol%）,arabinose and galactose accounted for75%of the total neutral sugar,and the highest Ca²⁺content（8.12 mg/g）.Scanning electron microscope showed that the pectin surface was smooth.ALP had the lowest molecular weight（192 k Da）,the highest extraction rate（25%）,the highest content of galacturonic acid（50.49%）,and scanning electron microscopy showed that the surface of pectin was loose and porous.The degree of methyl esterification of the three pectins ranged from 42.40%to 46.54%,belonging to low methoxy pectin with the same monosaccharide composition,belonging to RG-I pectin.The results of Fourier infrared showed that the three kinds of pectin of Gardenia jasminoides var.fortuniana contained many monosaccharides such as uronic acid and arabinose,which were consistent with the results of HPLC.The three kinds of pectin of Gardenia jasminoides var.fortuniana had semi-crystalline and amorphous structure.2.The rheological properties of pectin of Gardenia jasminoides var.fortuniana.The apparent viscosity,viscoelasticity and thixotropy of the pectin solutions of Gardenia jasminoides var.fortuniana extracted by three different methods were compared under different pectin concentration,temperature,p H and freeze-thaw conditions.The results showed that the apparent viscosity of the three kinds of pectin was pseudoplastic fluid with shear thinning,and the concentration was proportional to shear thinning behavior.The apparent viscosity of pectin decreased by changing p H and increasing temperature of pectin.During freeze-thaw,the apparent viscosity of ACP and HWP increased at 4℃and-20℃,while the apparent viscosity of ALP decreased.Viscoelastic results show that 4%and 5%ACP in linear viscoelastic region can form weak gel without any metal ions（G’>G"）,but the same concentration of ALP and HWP can not form weak gel（G’<G"）.The 4%and 5%ACP gels showed good thermal stability（G’>G"）in the dynamic rheological temperature test.The thixotropic results showed that the pectin extracted by the three methods could form thixotropic rings when the concentration was more than 2%,and the area of thixotropic rings increased with the increase of the same concentration.3.The emulsifying properties of pectin of Gardenia jasminoides var.fortuniana.O/W emulsion was prepared using 10%medium chain triglyceride as oil phase,and its emulsification properties were characterized.The results showed that the emulsion system prepared by 2%ACP,HWP and ALP showed good emulsification stability without demulsification when stored at 4℃and 25℃for 21 days.The emulsion prepared by ALP had no delamination when stored at 60℃for 21 days,while the ACP and HWP emulsions began to flocculate and coalesce on 21 days,leading to demulsification.The good emulsifying stability of ALP at 60℃was attributed to the formation of emulsion gel.The formation of emulsion gel of ALP may be related to the lower molecular weight of ALP,higher protein content（3.11%）,smaller particle size and its RG-I structure,but there was no significant correlation with the content and components of pectin amino acids.The stability of three kinds of Gardenia jasminoides var.fortuniana pectin emulsions was studied under different metal ions and ion strength.The results showed that the particle size of the three kinds of Gardenia jasminoides var.fortuniana pectin emulsions increased with the concentration of Na⁺,K⁺and Mg²⁺in the range of 0.1～0.3 mol/L,indicating that the metal ions would reduce the stability of emulsion.