Effect Of Dense Phase Carbon Dioxide On Physical Properties Of Litopenaeus Vannamei Myosin

Dense phase carbon dioxide(DPCD)is a very promising non-thermal food processing technology.Recent years,studies had found that: protein can be self-assembly to form gel induced by DPCD,and the properties of gel are superior to which induced by heated processing.This discovery provides a new method for protein gel products preparation.In this paper,the change of physical properties of morphology,solubility,turbidity,thermal denaturation and rheological properties of Litopenaeus vannamei myosin were investigated in order to explain the mechanism of myosin gel formation by DPCD processing.The main studied contents and results are as follow:(1)Microscopic alternation of shrimp myosin on different DPCD treament(5-30 MPa,30-60 ℃,5-30 min)were determined using Atomic Force Microscope(AFM).Results showed that: The shape of purified myosin molecules are ellipsoidal,smooth with clear edge and the average particle size is 4.78 nm.The average particle size of myosin molecules increased significantly(p<0.05)by DPCD processing,and formed into larger aggregates;with the increasing of pressure and time,the aggregates dissociated and dispersed gradually,and the average particle size of protein molecules decreased significantly(p<0.05).Pure heat treatment results show that,effects of temperature on myosin molecular particle size change trend were as same as the DPCD treatment,all increased as the temperature increased(p<0.05).(2)The effect of DPCD treatment(pressure 5-35 MPa;temperature 25-60℃;time5-60 min)on the myosin solution turbidity and solubility of myosin and SDS-PAGE electrophoresis pattern were investigated.Results showed that Under DPCD treatment,the solubility of myosin decreased significantly(p<0.05),and the myosin solution turbidity increased significantly(p<0.05).And the effects were closely related with myosin concentration,the higher myosin concentration was tesed,the more serious impact would get.SDS-PAGE electrophoresis showed that the color of the Heavy Chain of myosin(MHC)was gradually lighter treated by DPCD,and the band disappeared after a certain intensity.Compared with the single heating and atmospheric CO2 treatment,the results proved that the effect of CO2 molecules under pressure field was the main factor thatcaused myosin solution turbidity and solubility to change;At 10 MPa and 40℃ treat for20 min,myosin almost insoluble and the turbidity reach maximum,indicating that myosin denatured and gathered fully at this processing conditions,which lay the foundation for forming good gel.(3)The changes of thermodynamics during myosin gelation were detected by using Differential Scanning Calorimeter(DSC),and the thermal stability of myosin in different DPCD treatment conditions were observed.Results showed that :The purified myosin have an endothermic peak and an exothermic peak,the thermal transition temperature and enthalpy values which corresponded to endothermic peaks were 38.2℃ and 1.897 J/g,respectively;the thermal transition temperature and enthalpy values which corresponded to exothermic peaks were 42.7 ℃ and-1.351 J/g,respectively.Myosin would occur different degree of denaturation by DPCD processing,and proteins would be completely denatured when the pressure,temperature and time reaches a certain intensity,and formed into a new aggregate;concern about myosin thermal stability,at 25 MPa,35℃ for more than 5 min,DPCD could cause myosin denaturate to some extent,which indicated that more thermal stable aggregates would be obtained in this condition.(4)The dynamic rheological parameters of different myosin concentration solution,and effects of different DPCD treatment pressure(5-30 MPa),temperature(25-60℃),time(5-60 min)and heat treatment and atmospheric CO2 treatment on the dynamic rheological parameters of myosin solution were determinated by using Rheometer.Result showed that :Myosin solution could not be formed into gel at 1 mg/m L of protein concentration,when the concentration was higher than or equal to 5 mg/m L,it could be able to form gels.Myosin formed irreversible elastic gel at 10 mg/m L and 15 mg/m L of protein concentration;fish myosin solution could form more flexible gel at 15 mg/m L of protein concentration,but not irreversible elastic gel.Shrimp myosin solution(15 mg/m L)could form better irreversible elastic gel at 5MPa,35℃ treated for 30 min by DPCD;when treated by other DPCD processing conditions including heat treatment and the CO2 under atmospheric conditions,the elasticity of myosin gel were lower than those of untreated.(5)All in all,considred with the physical characteristics of the shrimp myosin,when myosin concentration of 15 mg/m L at 10 MPa,at the range of 25℃to 40℃ to treat for about30 min,DPCD can induce myosin form into better gel.The specific technological parameters still need to be further optimized by other index.