Mechanism Of Heat-Induced Gel Formation Of Porcine Myosin

Myosin is an important protein of muscle tissue,gel properties of myosin determine their water holding capacity(WHC),gel strength and viscoelasticity of meat products.The protein status,formation of aggregates and structural changes of myosin could be influenced by temperature,metal ion and other factors such as pH values,which results in changes of myosin gel properties.But mechanism of heat-induced gel formation of porcine myosin is still unclear.This study used porcine longissimus dorsi as experimental material,and a method to dissociate porcine myosin from muscle tissue has been established,the aggregation behavior and mechanism of heat-induced gel formation of myosin under different conditions of Na+?Ca2+and pH values were analyzed.Later the myosin-?-carrageenan complex was prepared and its gel formation mechanism was explored.This study provided the theoretical basis for studies of other fibrous protein gel formation mechanism,and practically guide meat productions with porcine myosin gel.The main results are listed as follow:(1)This study used porcine longissimus dorsi as experimental material,the chemical forces that restrict myosin dissociation were measured,the influence of pH values and ionic strength on porcine myosin dissociation was analyzed,and a method for dissociating porcine myosin from muscle was established.This study showed that hydrogen bond and hydrophobic interaction are the main chemical forces of restraining sarcoplasmic protein removal,ionic bond is the main chemical forces of restraining myosin dissociation.Solubility of sarcoplasmic protein reached 25.90%after 10 min's homogenization at pH 7,and solubility of myosin reached 41.95%after 20 min's homogenization when KCl content was 0.4 mol/L.(2)The turbidity,particle size,denaturation rate,structural stability of protein,Ca2+-ATPase activity,morphology of myosin aggregates and Raman spectra during thermal aggregation under different Na+,Ca2+ concentrations and pH values were measured.It showed that the denaturation temperature decreased from 42.8? to 40.3?,and the inactivation temperature of Ca2+-ATPase decreased from 60? to 50? with increasing Na+concentration from 0 mol/L to 2 mol/L.It demonstrated that the increased Na+concentrations promoted the exposure of hydrophobic groups,which enhanced the hydrophobic interaction between molecules.Besides,the denaturation temperature decreased from 40.2? to 36.9?,and the inactivation temperature of Ca2+-ATPase had no significant difference(p>0.05)with increasing Ca2+concentration from 0.01mol/L to 0.1 mol/L.It demonstrated that the increased Ca2+concentrations promoted the Ca2+-carboxyl bridges between molecules.TEM observation showed that the volume of protein aggregates increased significantly when Ca2+concentration increased to 0.1mol/L.,The denaturation temperature decreased from 40.2? to 36.9?,and the inactivation temperature of Ca2+-ATPase increased from 40? to 60? as pH increased from 5.5 to 8.5.It suggested that hydrophobic interaction between molecules and the cross-linking between protein aggregates enhanced with increased pH.(3)The WHC,gel strength,gel network structure and secondary structure of heat-induced gel of myosin under different Na+,Ca2+ concentrations and pH values were measured.It showed that WHC of the group treated with 0 mol/L Na+ was 2 7.69%,and gel strength was 0.75N when heated to 80?,significantly lower than other groups(p<0.05).The gel network structure could not be formed at this condition.The WHC reached to 70%,gel strength reached to 4.58N when Na+ content increased to 0.3 mol/L.The secondary structure of myosin did not change with increased Na+ concentration.The WHC decreased from 76.93%to 64.76%,and the gel strength increased from 4.58 N to 5.28 N when Ca2+content increased from 0.01 mol/L to 0.1 mol/L.The ?-helix content decreased from 47.26%to 40.58%as Ca2+ content increased.A rough,disordered and thick gel network was formed at high Ca2+concentrations.The WHC increased from 66.26%to 80.31%,and gel strength decreased from 4.24 N to 3.52 N when pH increased from 5.5 to 8.5.The uniform and ordered gel network was formed,and the?-helix content increased from 50.84%to 58.96%.(4)A composite gel was formed by porcine myosin and ?-carrageenan complexes.The WHC,gel strength,water distribution,network structure and Raman spectra of the composite gel were measured.The mechanism of heat-induced gel formation of myosin was verified.The WHC increased from 71.06%to 79.64%(p<0.05),and the gel strength increased significantly from 3.72 N to 4.43 N(p<0.05)with increasing Na+ concentration from 0.24 mol/L to 0.6 mol/L.The proportion of immobilized water increased from 73.58%to 79.07%,but the protein secondary structure did not change much.The WHC reached the highest value of 86.60%when the Ca2+ concentration was 0.04 mol/L.The proportion of immobilized water increased when Ca2+content was at low level.It may be due to the hydrophobic groups were exposed moderately,and a firm and uniform gel network was formed at low Ca2+concentration.The proportion of free water increased to 17.40%when Ca2+ concentration reached 0.06 mol/L.The hydrophobic groups were over-exposed,and large aggregates and cavities were observed when Ca2+ concentration reached 0.1 mol/L.In conclusion,this study confirmed that ionic bonding was the main chemical forces that restrict myosin dissociation.The mechanism of heat-induced aggregation and gelation of porcine myosin were proposed.It provided the practical guideline for meat products with porcine myosin gel in food industry.