Effect Of Multiple Freeze Thaw Cycles On The Quality Of Cihicken Breast Meat

Freezing has become the preferred choice in the global meat export market with avalue of more than $13 billion per year.Despite its ability to retain meat quality andsafety,the issues occurring because of the freeze-thaw cycles remain a major concern forprocessors and consumers.Temperature fluctuations attributed to freeze-thaw cyclingstimulates lipid oxidation and accelerate surface discoloration of meat.Protein oxidationis mostly ignored factor particularly in commercial broiler chickens.Therefore,morestudies are required to understand the impact of freeze-thaw cycles on protein stabilityand its relationship with lipid and protein oxidation.Such data regarding oxidationstudies are available for almost all meat categories except poultry especially under freeze-thaw environment.Therefore,it was important that this area,particularly proteinoxidation,could be pursued for further research.The objective of the study was to assessthe effects of multiple freezing-thawing cycles on physicochemical changes in chickenmeat muscles.This study was conducted to determine the effects of repeated freeze-thaw cycles(0,1,2,3,4,5 and 6)on physic-chemical changes and,lipid and protein oxidation inchicken meat.The frozen samples were subjected to either 0(fresh mcat,Control),1,3 or5 freeze-thaw cycles.The redness and yellowness decreased while lightness increasedwith increasing cycle numbers.The drip loss and thawing loss showed an increasingtrend with increasing freeze-thaw cycles.Water holding capacity was also decreased withincreasing number of freeze-thaw cycles.NMR relaxometry profile showed freeze-thawcycles decreased in content of immobilized water in meat when subjected to multiplefreeze-thaw cycles.Furthermore,Warner-Bratzler shear force was significantly decreasesuggesting less firmness.Differential scanning calorimetry profile indicated slightdenaturation of myosin and actin with repeated freeze-thaw cycles.The samples,however,exhibited remarkable changes in the first endothermic transitions during cycle 5only.DSC profile of the samples showed slight changes in the second endothermictransition of chicken breast samples compared with those of control.Thus,MFT cycles caused changes in color stability of broiler chicken breast,increase in drip and thawinglosses,decrease in WHC,decrease in immobilized water,decrease in shear force,as wellas increased denaturation of myofibrillar proteins,of chicken breast samples.Furthermore,the changes observed in the preliminary study were related tochanges in fatty acid and protein profiles of multiple frozen-thawed samples.Moreover,oxidative changes in lipids and proteins were indicated.Additionally,the changes inmyofibrillar and sarcoplasmic proteins were associated with oxidative changes in muscle,as well as changes in rheological properties of multiple frozen-thawed samples.Lipidprofile indicated significant increase in the concentration of SFA including capric,myristic,margaric and eicosanoic.The total saturated fatty acids were also found higherin C3 and C5 group compared to the fresh and C1(p>0.05).On the other hand,theconcentration of PUFA including linoleic,(C18:2)followed by linolenic(C18:3)andarachidonic(C20:4)significantly decreased in cycle dependent manner.Increasingfreeze-thaw cycles resulted in greater degree of lipid and protein oxidation as evidencedby higher contents of malondialdehyde and carbonyl compounds,and lower contents ofsulfhydryl groups.Total protein contents decreased in the chicken breast samplessubjected to multiple freeze-thaw cycles in cycle dependent manner.The SDS-PAGEbanding patterns of myofibrillar proteins indicated slight denaturation of myosin andactin with repeated freeze-thaw cycles.The banding pattern suggested that the bandintensity of myosin heavy chains was not significantly different.The intensity of bandsbetween 130 and 86 kDa decreased inconsistently as the number of freeze-thaw cyclesincreased.This indicated that the frozen storage might cause degradation or digestion ofmyofibrillar proteins.Furthermore,the oxidation caused by multiple freeze-thaw cyclesresulted in reduced band intensity of actin(45 kDa).Similarly,the SDS-PAGE bandingpattern of sarcoplasmic proteins showed degradation,indicated by loss in intensity ofbands from molecular weights 110,78,68,62,60,50 and 29 kDa(bands 2,3,5,6,8,9and 10 respectively).The rheological data of the chicken breast samples exhibited aremarkable decrease in gel forming ability from 51 to 57? for cycles 3 to 5 compared tothose of control.Additionally,from 57 to 80?,all the multiple freeze-thaw samplesexhibited decreases in G' compared to that of control.The marked changes in fatty acidcomposition,protein contents,as well as increased lipid and protein oxidation,denaturation and digestion of proteins,thus resulted in decreased gel forming ability of the chicken breast subjected to multiple freeze-thaw cycles.Finally,the relationship of structural changes in the chicken breast determined by TEM structure was established with 2-DE and WB.The spacing between the muscle fibers of chicken breast increased with increasing freeze-thaw cycles.The H-zone of all the chicken breast samples after multiple freeze-thaw cycles was lower than that of control,while the Z-line underwent remarkable shrinkage.The changes in myofibrillar structure were investigated by estimating the rates of protein degradation via western blotting and 2-DE.Significant correlation was observed between the intensities of protein spots of the 2D electrophoresis,out of which 78 were clearly identified.The freezing and thawing of chicken meat significantly altered almost all spot intensities on 2-DE gels.Western blots of samples from 0,1,3 and 5 freeze-thaw cycles of chicken breast indicated gradual decrease in band intensity of desmin from fresh 0 to 1,and cycle 1 to cycle 3.However,the band intensities from cycle 3 to cycle 5 were not significantly different.The increased degradation of desmin led to structural changes in chicken breast subjected to MFT cycles.In conclusion,the chicken breast subjected to MFT cycles underwent structural changes indicated by TEM structure mainly because of the degradation of myofibrillar proteins.