The Study On The Mechanism Of The Interaction Of Amino Acids With Metal Ion Forms Of ι-carrageenan

ι-carrageenan is the most highly sulfated of the helix-forming polysaccharides,but its gel properties are relatively weak.Metal ions played an important role in accelerating gelation ofι-carrageenan.For example,Ca²⁺could promote the aggregation ofι-carrageenan helices,the potassiumι-carrageenan was also confirmed to form double helix dimers.Amino acids are amphoteric electrolytes,and their electrification showed significant influences on the gel properties of hydrocolloids.However,there are few reports on the interaction between amino acidsand carrageenan.This paper aimed to investigate the gel properties of arginine,glutamine,glutamic acid and calciumι-carrageenan（CaIC）,potassiumι-carrageenan（KIC）mixed gels through the rheomer,the low field nuclear magnetic resonance,differential scanning calorimeter and cryo-scanning electron microscopy.At the same time,combined with infrared spectroscopy and X-ray diffraction,the interaction mechanism between amino acids and CaIC and KIC was further interpreted.The K⁺,Na⁺,and Ca²⁺contents of CaIC were changed from 3.258%,2.434%,and0.909%to 0.595%,0.618%,and 6.657%,respectively,as determined by atomic emission spectrometry.The K⁺,Na⁺,and Ca²⁺contents of KIC were changed to 6.407%,0.622%and0.552%.The pH measurement of the mixed gels of amino acid and CaIC,KIC showed that the addition of amino acid acted to adjust the pH of the CaIC,KIC gel systems.The rheological properties of the amino acid-CaIC mixed gels showed that the maximum the elastic modulus（G’）,theviscosity modulus（G’’）and complex viscosity were obtained at concentrations of 0.02%arginine and 0.1%glutamine,respectively.There was no significant difference in gel-sol transition temperature（T_m）between arginine-CaIC（ACaIC）gels,while the T_m of GCaIC was significantly decreased at the concentration of 0.2%glutamine.With the increase glutamic acid concentration,the G’,G’’and complex viscosity of glutamic acid-CaIC（ECaIC）decreased gradually,while T_m increased significantly.The low field nuclear magnetic resonance（LF-NMR）results showed that amino acid-CaIC gels were mainly composed of free water.The addition of arginine increased the position of T₂₃,which reduced the fluidity of free water.With the increase glutamic acid concentration,the position of T₂₃ decreased gradually and then increased,and the worst fluidity of free water was obtained at concentrations of 0.2%glutamic acid.However,glutamine had no significant effect on the fluidity of GCaIC free water.However,glutamine had no significant effect on the fluidity of GCaIC free water.The results of thermal property analysis revealed that thermal degradation temperature of CaIC was improved from 181.29℃ to 255.30℃、228.41℃ and 218.70℃ by arginine,glutamine and glutamic acid,respectively.By apparent morphology observation,it was found that arginine could induce CaIC to form a relatively complete gel network structure,the 0.2%concentration of glutamic acid could also promote the formation of uniform pore network structure of the CaIC gel,while glutamine had no significant effect on the formation of CaIC gel network.The infrared spectroscope results showed that the hydroxyl characteristic absorption peaks of the amino acid-CaIC mixed gels were shifted.Arginine and glutamine led to characteristic peaks of amide I band in CaIC infrared spectra,while glutamic acid led to characteristic peaks of amide II band in CaIC infrared spectra.X-ray diffraction results showed that the addition of amino acids resulted in a decrease in the“bun-shaped”diffraction peaks of CaIC.In summary,there was mainly electrostatic interaction between arginine and CaIC,while glutamine was mainly accumulated in the CaIC gel network by filling.The rheological properties of the amino acid-KIC mixed gels showed that arginine,glutamine and glutamic acid could reduce the frequency dependence of KIC and increase its temperature stability.The maximum modulus and complex viscosities were obtained at concentrations of 0.05%arginine,0.2%glutamine and 0.1%glutamic acid,respectively.The addition of arginine,glutamine and glutamic acid increased the T_m of CaIC from 37.19℃ to46.06℃,42.89℃ and 42.97℃,respectively.LF-NMR results showed that arginine and the0.2%concentration of glutamic acid decreased the fluidity of mixed gels free water,while glutamine increased the fluidity of mixed gels free water significantly.Thermal property analysis results showed that the maximum thermal degradation temperature was obtained at concentrations of 0.2%arginine and 0.02%glutamine,respectively,while the degradation temperature gradually decreased with the increase glutamic acid concentration.The apparent morphology observation showed that arginine and glutamic acid promoted the formation of KIC gel network,and glutamine resulted in CaIC to form a gel network with relatively thin pore walls.The results of infrared spectroscope indicated that there was hydrogen bond interaction between amino acids and KIC.Arginine and glutamine also led to characteristic peaks of amide I band in KIC infrared spectra,and glutamic acid led to characteristic peaks of amide II band in KIC infrared spectra.X-ray diffraction results showed that the addition of amino acids had no significant effect on the“bun-shaped”diffraction peaks of KIC.All the results also indicated that there was mainly electrostatic interaction between arginine and KIC,while glutamine was mainly accumulated in the KIC gel network by filling.