| Ovalbumin,as the kind of protein with the highest content in egg white,prone to be oxidized,which result in structural changes,and thusaffects its functional properties.This study firstly investigated the effects of oxidation on the functional properties of ovalbumin under free radical oxidation system.The initial ovalbumin oxidation behavior was obtained through analyzing the molecular characteristics and structural changes of ovalbumin induced by oxidation.Besides,the relationship between egg protein oxidation and its functional characteristics were determined.Moreover,a preliminary product model was constructed via applying the production practice based on the change of the functional characteristics of the oxidation process.(1)The influence of oxidation treatment on the functional properties of ovalbumin was preliminary clarified.In this study,the albumin was firstly isolated and purified by polyethylene glycol fractionation,followed by oxidizing by FeCl3/Asc/H2O2 radical oxidation system.The obtained oxidized samples were then used to determine the carbonyl and mercapto groups which could reflect the degree of protein oxidation,then the appropriate oxidation system was optimized with 10 mmol/L H2O2 and oxidation time of 3.0 h.With this established oxidation system,the free amino,gel rheological properties,texture characteristics,emulsifying and stability together with foaming and stability were determined.The results revealed that the free amino content of ovalbumin after being oxidized for 3.0 h decreased by 13.6%compared with the control group,the gel elasticity decreased,while the gel hardness the water retention decreased by 49.1%and 29.0%,respectively.The microstructure of the gel was also transformed from a dense network structure before being oxidized into a three-dimensional network.The emulsification and emulsification stability of ovalbumin showed a similar trend of increasing first and then decreasing,the maximum of emulsifying activity was 13.45 m2/g with the oxidation time of 2.5 h while the maximum stability of emulsification was 109.51%at 1.5 h,and the time point of the two maximum value was inconsistent.The foaming ability was in a significant upward trend,reaching a maximum of 175.67%at 3.0 h,while the foaming stability showed a trend of increasing first and then decreasing,reaching a maximum of 80.53%at2.0 h,and then decreased significantly.In conclusion,the results have shown that oxidation could alter the binding manner of ovalbumin peptide bonds and the arrangement of amino acid residues,and further change the textural characteristics,hence display different degrees of reduction in the gel elasticity,gel hardness and water retention,whereas significantly enhance the protein foaming.Under oxidation conditions with low concentration,the stability of protein foaming,emulsification and stability could be improved,but they could be inhibited under higher conditions.(2)The effect of oxidation treatment on molecular and structural characteristics of ovalbumin was studied.Based on the above results,the effect of free radical oxidative system on the molecular characteristics of ovalbumin was studied by applying Zeta potentiometer,DSC,DNS fluorescent probe,SDS-PAGE and MALDI-TOF-MS.Then the effect of oxidation on the structure of ovalbumin was investigated by UV spectroscopy,Synchronous fluorescence spectrum,infrared spectroscopy and circular dichroism.During the oxidation process from 0 h to 3.0 h,Ovalbumin can produce multimersthe,protein solubility decreased by 4.897%and the Zeta potential was reduced by 12.5 mV.Besides,the particle size distribution shifted to the larger particle size and increased by 167%,and the transition temperature decreased by 4.3℃,the enthalpy decreased by 0.53 J/g,the hydrophobicity gradually increased.Moreover,the side chain groups of tryptophan and tyrosine residues changed obviously,and the α-helix in the secondary structure of protein decreased by 2.4%,irregular curl increased significantly,the a-helix,β-angle reduction and β-fold content obtained from the circular dichroism increased slightly,irregular curl increased significantly with an increase ratio of 4.6%,two results are basically identical.Hence the data elucidated that the peptide chains would break during the process of oxidation,while the side chain amino acid would be oxidize-modified and the protein would be covalently cross-linked,and the connection mode of protein will change,thus leading to transformation in protein conformation which further affect the functional properties of protein.(3)The possibility of applying the oxidized ovalbumin as the substitutes of tyrosine sodium in whip cream.We then made use of mild oxidative ability which could significantly improve the emulsification of ovalbumin and combined this with the whipping cream technique,the difference would be systematically evaluated by determining the particle size,texture,whipping bubble rate and sensory assessment,The experimental results showed that the hardness of whipped cream decreased gradually with increasing the content of oxidized ovalbumin,while the viscoelasticity exhibited the opposite tendency.In detail,the viscoelasticity increased from 27.6 to 30.3 when the content of added ovalbumin increased from 0.5 times as much as that of tyrosine sodium to 1.5 times while the whipping bubbling rate increased from 321%to 346%.Besides,the whiteness of the cream also increased,the whiteness of the sodium tyrosine group(control group)and the oxidized ovalbumin substitute with 1.5 times as much as the content of control group were both 95.Moreover,the average particle size of the cream emulsion was also slightly enhanced.In the sensory evaluation test,the viscosity and taste evaluation were lower in group 1(the mass ratio of content of oxidized ovalbumin to sodium tyrosine was 0.5),and there was no significant difference of the astringent sense between the control group and group 1.Of note,the viscosity and greasy taste score of group 2(the mass ratio of content of oxidized ovalbumin to sodium tyrosine was 1)was low and achieved the lowest evaluation among three groups.However,there was no significant difference of the overall index between the group 3(the mass ratio of content of oxidized ovalbumin to sodium tyrosine was 1.5)and control group.The comprehensive test results then came to a conclusion that the addition of oxidized ovalbumin with the content of 1.5 times as much as that of sodium tyrosine could be the alternatives of raw materials in whipping cream. |
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