Study On Structure And Functional Properties Of High Methoxyl Pectin

In this study,high methoxyl pectin(HMP)with different degree of esterification(DE)was prepared by alkali treatment,and its physicochemical properties and structure were characterized and analyzed.HMP-calcium gel was prepared and its gel formation mechanism was explored.The effects of DE and Ca²⁺concentration on physicochemical properties,rheological properties and microstructure of HMP-calcium gel were emphatically analyzed.HMP emulsion gel was prepared and its mechanism was analyzed.The effects of DE and Ca²⁺concentration on the emulsifying capacity,rheological properties and emulsion stability of HMP emulsion gel were emphatically studied.The results are as follows:1.The basic physical and chemical properties and structure of HMP with different DE showed that with the decrease of DE,HMP carried more carboxylic acid groups,the absolute value of zeta potential increased,and the molecular weight of pectin decreased.Gal A content decreased,while RG-I content and branching degree increased.The conformation of pectin changed and more regular helix structure was produced.The Structural characteristic peak did not change obviously after de-esterification.The thermal stability of pectin decreased slightly with the decrease of DE.AFM images showed that with the increase of de-esterification degree,the molecular structure of HMP became shorter,and the degree of entanglement between molecules became weaker.2.The preparation and properties of HMP-calcium gel showed that pectin concentration,p H and Ca²⁺concentration all had effects on the properties of HMP-calcium gel.The apparent viscosity of calcium gel increased with the increase of pectin concentration.The sensitivity of HMP to calcium increased with the increase of p H.In a certain range,the apparent viscosity of pectin calcium gel increased with the increase of Ca²⁺concentration,but the viscosity limit value existed.The DE and Ca²⁺concentration had a significant effect on the functional properties of HMP-calcium gel.The potential absolute value of calcium gel decreased with the increase of Ca²⁺concentration and DE.The particle size of calcium gel increased with the increase of Ca²⁺concentration and DE.Under low Ca²⁺concentration,the rheological properties of calcium gel were more obviously different.Calcium gel with higher esterification degree showed better gelling characteristics.Under high Ca²⁺concentration,the rheological properties of calcium gel with different DE were tended to be similar to rheological properties of calcium gel with high DE.In AFM,the structure of calcium gel with low DE is short and fine,and the network structure is scattered and fragmented.Calcium gel with high DE is thicker,the network is complex and the gap is small,showing a better gel network structure.3.The preparation and properties of HMP emulsion gel showed that pectin concentration,p H and Ca²⁺concentration all had a positive effects on pectin emulsifying properties.High concentration pectin provided more hydrophobic groups;High p H can enhance the degree of protonated carboxylic acid and increase the electrostatic repulsion;The Ca²⁺concentration had the most significant effect on the emulsifying ability of pectin.Through crosslinking HMP,calcium ion increased the viscosity of continuous phase,the density of hydrophobic groups on the water oil interface and the steric hindrance between droplets,and optimized the ability of stabilizing droplets;Too high Ca2⁺concentration can significantly reduce the negative charge of pectin,reduce the repulsion between droplets,intensify the aggregation and flocculation of HMP,which is not conducive to the stability of emulsion droplets.The DE and Ca²⁺concentration had a significant effect on the properties of HMP emulsion gel.The results showed that without adding calcium ion the higher the DE of pectin was,the stronger the emulsifying ability was;when at appropriate Ca²⁺concentration,HMP with different DE had similar emulsifying ability.When the Ca²⁺concentration was excessive,the emulsifying ability of HMP with higher DE decreased more obviously.The HMP emulsion gel with high DE has stronger freeze-thaw stability and thermal stability.When the Ca²⁺concentration was 5 mmol/L,the centrifugal stability,freeze-thaw stability and thermal stability of the emulsion gel were the best.