Study On Effects Of Salt And High Pressure Treatment On Properties And Chemical Forces Of Myofibrillar Protein Gel And The Regulation Mechanism

The formation of myofibrillar protein?MP?gel is largely depended on chemical forces.Investigating chemical forces of MP gel can provide theoretical guidance for controlling MP gel properties.This dissertation studied the effects of ionic strength,partial salt substitution and high pressure treatment on chemical forces?disulfide bond,hydrophobic interactions,hydrogen bond and electrostatic interactions?and functional properties?texture,rheology and water holding capacity?WHC??of MP gel,and discussed the regulation mechanism of chemical forces on gel properties under the three different treatment mentioned above,details as follows:Chapter two: Gel properties?textural properties,rheological properties and WHC?under different ionic strength?0.2-0.6?were investigated by texture analyzer,rheometer and centrifugation method.Chemical forces?disulfide bond,hydrophobic interactions,hydrogen bond and electrostatic interactions?were tested by UV spectrophotometer,fluorescence spectroscopy,Raman Spectroscopy and zeta potential.The results showed that with the increase of ionic strength,the gel hardness,G' and WHC were significantly enhanced?p<0.05?.With the increase of ionic strength,total SH group content decreased,surface hydrophobicity and normalized intensity of of Raman spectrum 760 cm^-1 band were strengthened,normalized ratio of I850/I830 increased and the absolute value of zeta potential gradually decreased,which suggested that the increased ionic strength contributed to the formation of disulfide bonds,the enhancement of hydrophobic interactions and protein-water hydrogen bond,and the weakness of electrostatic interactions.High quality of MP gel induced by higher ionic strength was due to the strength of attractive force and weakness of repulsive force.The correlation analysis between chemical forces and gel properties indicated that gel hardness,G' and WHC were negatively correlated with total SH group content and the absolute value of zeta potential,positively correlated with hydrophobic interactions?S0-ANS and I760?and protein-water hydrogen bonds?I850/I830?,and with no significant correlation with reactive SH group content,which suggested that the decrease of total SH group content and absolute value of zeta potential,the increase of hydrophobic interactions and protein-water hydrogen bonds were contributed to the strength of gel hardness,G' and WHC.Chapter three: The effects of low sodium and partial substitution of NaCl with KCl,MgCl₂ and CaCl₂ on chemical forces and gel hardness were investigated,the relationship between disulfide bond,hydrophobic interactions,hydrogen bond,electrostatic interactions and gel hardness under low sodium condition and different salt substitution of NaCl were analyzed.The results showed that compared with normal sodium?0.6 mol/L NaCl?MP gel,the total SH group content of low sodium?0.4 mol/L NaCl?MP gel was relatively higher,the normalized intensity of 760 cm^-1 band,normalized ratio of I850/I830 and absolute value of zeta potential all decreased,which suggested that low sodium was unbeneficial for the formation of disulfide bonds and weakened the hydrophobic interactions,electrostatic interactions and protein-water hydrogen bonding in MP gel.Partial substituting NaCl with KCl?0.4 mol/L NaCl + 0.2 mol/L KCl?had no significant impacts on chemical forces.As to partial substitute of NaCl with MgCl₂ and Ca Cl₂?0.4 mol/L NaCl + 0.1 mol/L MgCl₂,0.4 mol/L NaCl + 0.1 mol/L CaCl₂?,the insignificant changes of total SH content showed partial substituting NaCl with MgCl₂ and CaCl₂ had no significant impacts on disulfide bonds,the increase of S0-ANS and normalized intensity of 760 cm^-1 band suggested stronger hydrophobic interactions,the increase of normalized ratio of I850/I830 suggested stronger protein-water hydrogen bonding,the decrease of absolute value of zeta potential indicated the weakened electrostatic interactions?p<0.05?,the strengthened attractive force and weakened repulsive force led to the enhancement of gel hardness.Chapter four: The effects of atmospheric pressure?0.1 MPa?and high pressure treatment?100-500 MPa?on MP conformation,MP gel microstructure,gel properties and chemical forces were investigated.The results showed that high pressure treatment had no significant impact on protein primary structure,contents of ?-helix and ?-sheet decreased,and contents of ?-turn and random coil increased,high pressure treatment had destructive effects on tertiary structure and quarternary structure of MP.Moderate high pressure??200 MPa?treatment improved gel microstructure,while severe high pressure??300 MPa?treatment was destructive to gel microstructure.As high pressure increased from 0.1 MPa to 200 MPa,gel hardness and WHC significantly increased?p<0.05?,when pressure exceeded 200 MPa,gel hardness,G',G" and WHC decreased significantly.As pressure increased from 0.1 to 200 MPa,the total SH content declined,while surface hydrophobicity,normalized intensity of 760 cm^-1 band,normalized ratio of I850/I830 and absolute value of zeta potential increased,which suggested moderate high pressure treatment was conducive to the formation of disulfide bonds,the enhancement of hydrophobic interactions and protein-water hydrogen bonds and electrostatic interactions.When high pressure further increased?300-500 MPa?,the total SH group content decreased,surface hydrophobicity no more increased,normalized intensity of 760 cm^-1 band and normalized ratio of I850/I830 decreased and the absolute value of zeta potential increased,which suggested the formation of disulfide bonds,the weakness of hydrophobic interactions and protein-water hydrogen bonds,and the strength of electrostatic interactions.Moderate high pressure?? 200 MPa?treatment strengthened gel properties,while severe high pressure??300 MPa?treatment weakened gel properties.High pressure treatment at 200 MPa significantly strengthened MP gel properties?p<0.05?.Chapter five: The PCA?principal component analysis?was used to analyze the experiment data of chapter 2-4,and found that under different ionic strength,the regulation of chemical forces on WHC of MP gel was achieved by regulating hydrophobic interactions and electrostatic interactions,the regulation of chemical forces on G' and gel hardness by partial substitute of NaCl with KCl,MgCl₂ and CaCl₂ was achieved by changing electrostatic interactions.The regulation of chemical forces on WHC of MP gel treated by high pressure was achieved by denaturing protein,exposing inner groups?sulfhydryl groups and tyrosine residues?,to improve the formation of disulfide bonds and protein-water hydrogen bonds.