| Myofibrillar proteins gel property was one of the most important processing functional characteristics in meat processing.Myofibrillar protein gel plays an important role on structure and water holding capacity of products.Protein oxidation phenomenon is common during processing and storage of meat and meat products.Protein oxidation caused physicochemical changes in protein,and affected the functional characteristics of protein,such as gel properties,water holding capacity.However,little information is available on the effect of protein oxidation on the protein thermal gel formation process and its stability.Therefore,the objective was to study the impact of oxidation on thermal gelation and storage stability of thermal gels of chicken breast myofibrillar proteins by using a hydroxyl radical-generating system basis on the topic of exudation water in the meat batter products.By using low field nuclear magnetic resonance(NMR)and Raman spectroscopy technique,the relationship between protein oxidation and water hololding in thermal gelation in the level of proton and molecular was also investigate to provide theoretical foundation in terms of the water holding capacity problem of meat batter products.The contents and results are as follows:1.Determination of protein concentration in the oxidizing systemThe objective of this chapter was to study the effect of protein concentration on oxidation and subsequent gel properties of chicken breast myofibrillar proteins to find a proper protein concentration used in the oxidizing system for the following studies.Firstly,oxidant(a hydroxyl radical-generating system,HRGS,0.01 mmol/L FeCl3,0.1 mmol/L Vc,1 mmol/L H2O2)was added to the different concentrations of myofibrillar proteins(20,40,60 mg/mL),and then oxidized for 24 h at 4?.After 24 h,precipitation of oxidized myofibrillar proteins was obtained by the centrifugation,then carbonyl contents was detected,the left proteins precipitation was used to prepare thermal gels,detecting the Free sulfhydryl groups(FSH),Water holding capacity(WHC),microstructure and texture of its gels in order to investigate the effect of protein concentration in the oxidizing system on chicken breast myofibrillar proteins oxidation and gel properties.The results showed that with the increase of protein concentration,the content of carbonyl group of oxidized myofibrillar protein was decreased.Therefore,the increased protein concentration led to the reduction of myofibrillar protein oxidation in the oxidizing system(P<0.05).Meanwhile,with the increased protein concentration,the content of FSH was significantly increased(P<0.05),the WHC of the gel was gradually increased while the gel hardness was decreased.Moreover,the microstructure results showed that the uneven and loose network structure of gels with some large pores and protein aggregates were observed in low protein concentration treatment.However,a uniform and dense network structure was presented in high protein concentration treatment.Therefore,the protein concentrations have a significant impact on the myofibrillar protein oxidation and the subsequent thermal gel properties in the hydroxyl-generating system.Taking both the effect of protein concentrations on the carbonyl content of myofibrillar protein after oxidative treatment and the operability of the establishing process of oxidizing system into consideration,the protein concentration of 20 mg/mL was selected for the oxidizing system used in the follow-up studies.2.Effect of oxidization on the thermal gel properties of chicken breast myofibrillar proteinsTo investigate the relationship between protein oxidation and problem of exudation water in comminute meat products,the effect of protein oxidization on WHC,water distribution,texture and microscopic structure of chicken myofibrillar protein heat-induced gel were investigated.Results showed that the myofibrillar protein oxidation significantly reduced its thermal gel hardness(P<0.05)with the increase of oxidation degree.Compare to control samples,the groups 0.1,1,5 mmol/L was descended 34%,39%,51%,respectively.At the same time,high oxidation thermal gel network structure is not uniform,evacuation,and the protein aggregation occurring in the gel network structure induced large holes and cracks,and caused immobilized water transforming to free water.Compared to control samples,0.1 mmol/L significantly increased the area of peak T22 with 3.6%.However,the groups of 1,5 mmol/L significantly decreased the area of peak T22(P<0.05),which decreased 6.7%and 13.2%,respectively.Protein oxidation significantly increased the content of free water that was easy to be lost,the groups 1,5 mmol/L significantly inceased the area of peak T23(P<0.05),which inceased 58.0%and 78.8%,respectively.Therefore,protein oxidizing treatment resulted in decreased WHC of thermal gel,6.6%and 13.2%WHC for 1,5 mmol/L,respectively were significantly lost(P<0.05)compared to control samples.Thus,protein oxidation treatment before gelation influenced the microscopic structure,texture,WHC and the water distribution of gels,confirming that there was relationship between the protein oxidation and the phenomenon of exudation water in thermal gel.3.Effect of oxidation on the process of thermal gelation of chicken breast myofibrillar proteinThis study was designed to investigate the effect of oxidation on the thermal gelling properties of chicken breast myofibrillar protein and to determine the mechanism.20 mg/mL chicken breast myofibrillar protein were treated with oxidizing system(0.01 mmol/L FeC13,0.1 mmol/L Vc,0,0.1,1,5 mmol/L H2O2).Then,some treated myofibrillar proteins were used to detect rheological properties,and others were used to prepare heat induced gels.Protein samples were in dynamic heating conditions(1.5?/min)from 20?to different endpoint temperatures of 30?,40?,50?,60?,70? and 90? and holded 20 min at each endpoint temperature to simulate the process of thermal gelation.Protein samples at each endpoint temperature were detected for WHC,water distribution.Secondary protein structure and gel microstructure at 90? were determined.The results showed that:with the gradually increased temperature during the process of protein gelation,the WHC of each group was significantly decreased(P<0.001),and the higher degree of protein oxidation,the lower WHC of protein gels,and it reached a significant level from 60?(P<0.01).High temperature heating at 90? enhanced the negative influence of protein oxidation on WHC,and improvement of WHC of the low degree of protein oxidation group was disappeared.Middle and high extent oxidation accelerated T22 shifting to short time,decreasing molecular distance,they increased the width of the peak of T22 that decreased the uniformity of distribution of water of T22,and accelerated the decrease of the content of T22 distribution water,the extent was increased with higher oxidizing level,which caused water of T22 distribution shifted to water of T23 distribution(related to free water)and to quicken the increase rate of the relative percentages of the area of peak T23.However,low extent oxidation slow down the decrease of water of T22 distribution that improved samples holding this kind of water,reached better state at 70?,and slow down the increase of water of T23.Low extent oxidation was good for forming?-sheet and ?-turns(P<0.05),but this phenomenon did not occured in high content oxidation group as more ?-helix structures were observed.In addition,protein oxidation decreased the storage modulus(G'),especially after 70?,and with the greater degree of protein oxidation,the storage modulus(G')was lower.At the same time,thermal gel of high oxidation groups shoed network structure with non-uniform,evacuation,and large protein aggregation,which induced large holes and cracks in thermal gel at 90?.Therefore,the level of protein oxidation has a significant effect on the process of thermal gelation of myofibrillar protein.Compared with low degree of protein oxidation,higher level of protein oxidation caused the deterioration of network structure of the protein gel,the reduction of the content of bound water and immobilized water and the increase of the content of free water can reduce the WHC of protein gels.Higher level of protein oxidation was not suitable for secondary protein structure holding more ?-sheet and ?-turns,inducing poor structure and texture of thermal gel at 90?.High temperature heating at 90?enhanced the negative effect of protein oxidation.4.Effects of oxidation on the storage stability of chicken breast myofibrillar protein heat-induced gelsThe objective of this study was to investigate the effect of various degrees protein oxidation on the storage stability of chicken breast myofibrillar protein heat-induced gels.20 mg/mL chicken breast myofibrillar protein were treated with oxidizing system(0.01 mmol/L FeCl3,0.1 mmol/L Vc,10mmol/L H2O2).Then,treated myofibrillar proteins were adjusted to 40 mg/mL and heated from 20? to 90?(1.5?/min)to prepare gels.Gels were stored at 4?.Carbonyl content,texture,microstructure,WHC and water distribution was detected in the zero days,the seventh days,the fourteenth days,the twenty-first days and twenty-eighth days,respectively.The results showed that:protein oxidation had significant effects on the WHC,carbonyl content,texture,transversal relaxation time T2 and the relative percentages of the area of T22 of gels(P<0.05).The microstructure gel structure was evacuation,with higher extent break and faster deterioration rate.In addition,there were significant interaction between protein oxidation treatment and storage time on the carbonyl content and the transverse relaxation time T2b and T22 of gels(P<0.05).Before the fourteenth day,oxidation treatment accelerated the protein oxidation in gels,influenced the microstructure and texture of gels,affected the water distribution and accelerated the rate of shifting from immobilized water to free water,thus leading to decreased WHC of gels.But during longer storage,each parameter did not change significantly(P>0.05).Therefore,in certain storage period,the oxidation of breast myofibrillar protein had a negative impact on the WHC and microstructure stability of gels,and accelerated the decrease of WHC and the damage of gel network structure.Overall,these results indicated that exudation water of thermal gel have a relationship with protein oxidation. |
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