Structural Characterizations And Emulsifying Properties Of Chicory Root Pectin

Chicory root pulp is regarded as a potential source for extracting pectin polysaccharide since it contains abundant pectin.However,due to the late start of the research and the lack of systematicness,there is no breakthrough on the key issues such as structure-activity relationship and application characteristics of chicory root pectin?CRP?.In this paper,CRP was chosen as the research object.The effects of extraction technology on pectin yield,structure and emulsification characteristics were investigated firstly,and the relationship between the molecular structure of CRP and its emulsifying properties was elaborated with the reference of sugar beet pectin?SBP?.Then,the effects of environmental factors including pH value and ionic strength on the emulsifying properties of CRP were investigated.The electrostatic interaction between CRP and whey protein isolate?WPI?was further induced to improve the emulsifying properties of CRP.The main conclusions are as follows:Extraction technology of CRP was investigated.Microwave-assisted extraction?MAE?and conventional heating extraction?CHE?were used to extract CRP.The molecular structure and emulsifying properties of CRP were characterized by weight average molecular weight?Mw?,infrared spectrum,scanning electron microscope and particle size.The two methods had no significant effect on the galacturonic acids,degree of methyl esterification and acetylation of CRP.The yield of pectin had increased by prolonging extraction time of CHE,but the molecular weight of pectin had significantly reduced.There was a significant positive correlation between microwave treatment time and extraction yield as well as Mw.Both the yield?12.7%?and Mw?321 kDa?of pectin extracted by microwave treatment for 120 s?MAE120?were highest among all samples,and the degradation degree of the molecular structure of pectin was low.Compared with the sample extracted by hot acid treatment for 1 h?CHE1?,the emulsifying stability of the emulsion prepared by MAE120 was poorer,and the D₄₃ value?4.9?m?of the emulsion prepared by MAE120 was significantly higher than that of CHE1?1.4?m?after a storage for 7 days at 55?.The relationship between molecular structure and emulsifying properties of CRP was investigated.SBP was used as a reference to evaluate the emulsifying properties of CRP objectively.CRP and SBP had similar emulsifying properties,although they had different structural characteristics such as degree of acetylation,protein content,amino acid composition,degree of branching and ferulic acid content.The emulsifying capacities of both CRP and SBP had decreased after protease hydrolysis.The D₄₃ value of the emulsions prepared by CRP and SBP had increased from 1.2?m to 2.3?m and 1.1?m to 2.7?m respectively,indicating that the emulsifying capacities of the pectins were determined by the covalently bound protein.With the increase of pectin concentration,the D₃₂ values of the emulsions prepared by CRP and SBP decreased from 1.3 to 0.6?m,from 1.7 to 0.6?m respectively.However,at low pectin concentrations?0.25%⁰.5%?,the particle size of CRP emulsion was smaller than that of SBP emulsion.It waspresumed that the relationship between structure and emulsification properties of CRP was that the proteinaceous moiety firstly adsorbed to the surface of oil droplets as anchors,and then the carbohydrate moiety formed a hydration layer on the surface of oil droplets.The effects of environmental factors on the emulsifying properties of CRP were investigated.The effects of pH value and ionic strength on emulsifying properties of CRP were explored by measuring zeta potential,hydrodynamic radius?R_h?,average particle size and distribution of emulsion,as well as the microstructure of emulsion,compared to SBP.From pH 2 to 6,the change of zeta potential?about 30 mV?of CRP in solution was similar to that of SBP,while the R_h values of CRP?186.5²77.1 nm?were always significantly lower than that of SBP?254.1⁷14.5 nm?at the same pH value.The D₄₃ values of CRP emulsion were significantly dependent of pH.At low pH?pH 2³?,the emulsifying activity and stability of CRP were better than that of SBP,because CRP molecules had higher flexibility and lower extensibility in aqueous phase,which was more conducive to its adsorption to the surface of oil droplets.With the increase of pH,the D₄₃ values of fresh CRP and SBP emulsions varied from 1.2 to 1.3?m and 1.0 to 2.2?m,respectively.The emulsifying activities of CRP and SBP emulsions were almost independent of Na⁺?25¹00mM?,while the CRP emulsion was more sensitive to Ca²⁺?25¹00 mM?.The emulsifying properties of CRP were improved by electrostatic combination with WPI.CRP and WPI formed stable soluble complexes in the range of pH 2.9⁴.0,and the emulsifying properties of CRP-WPI complex depended on the ratio of the two complexes?r,WPI/CRP,w/w?.The suitable r of CRP-WPI system ranged from 0.25 to 1.Too large or too small r value would not conducive to the emulsion stability of the complex emulsion.On this basis,the effects of Na⁺and Ca²⁺on the emulsifying properties of CRP-WPI complex were investigated.When the Na⁺concentration ranged from 5 to 100 mM,the D₄₃ values of the CRP-WPI complex emulsion were lower than that of the control group.When the Na⁺concentration was 20 mM,the D₄₃ value of the composite emulsion decreased to its minimum?0.6?m?,indicating that the electrostatic shielding had improved the emulsifying activity of the emulsion.With the addition of 50 mM Ca²⁺,the D₄₃ value of CRP emulsion had reached 2.1?m,while the D₄₃ value of CRP-WPI was smaller than 1.4?m.Therefore,the emulsifying activity and stability of CRP emulsion and its resistance to Ca²⁺had improved to a certain extent,through the electrostatic interaction with WPI.