Studies On Gel Properties Of PSE-like Chicken Breast Meat

Pale,soft,and exudative（PSE）-like poultry meat quality defect affects its sensory qualities and the purchasers’ desire,and impaired functional properties and cooking yield when used in further processed products.The occurrence of PSE-like chicken meat is high for the poultry industry worldwide,therefore,PSE-like poultry meat quality defect has been much more concerned in the poultry industry.It has become one of the great challenges in the context of the functional properties of meat and meat products for meat scientists and processing researchers.A better understanding in mechanisms of inferior functional properties of PSE-like chicken breast meat and exploring a novel technology to modifying its functional properties are essential for poultry industry to decrease the economic loss.Therefore,in my study,physiochemical and thermal gelling properties of PSE-like and normal chicken breast meat were compared and estimated,then protein characteristic changes of PSE-like and normal meat processing were evaluated to find the relationship between protein structures changes and functional properties,then the mechanisms in the differences of gel properties of natural actomyosin extracted from PSE-like and normal chicken breast meat were clarified,and the effect of high intensity ultrasound treatments on the functional properties of PSE-like chicken breast meat batter were investigated.The detailed contents and results were showed as followed:1.A comparative study of physiochemical and thermal gelling properties of PSE-like and normal chicken breast meatThe objective of this study was to make a thorough understanding of how much the difference in protein functionality related to two poultry meat qualities.PSE-like(L*>53,pH_24h<5.7)and normal(46<L*<53,5.7<pH_24h<6.1)skinless,boneless broiler chicken breast muscles（M.Pectoralis major）were collected from the deboning line of a major Chinese commercial plant.We made the unified meat batter preparation（the same amounts of protein and salt）in the experimental design,then evaluate the differences between pale,soft,exudative（PSE）-like and normal chicken breast meat in the chemical composition,pH,color,water holding capacity,textural properties,salt soluble proteins（SSP）extraction as well as dynamic rheological properties.The results are showed that:compared with normal meat,PSE-like chicken meat showed significantly lower protein content（P<0.05）.It had a significantly higher L*values,lower pH and SSP extraction contents by two different shear methods（P<0.05）.Dynamic rheology showed that PSE-like meat batter had the different viscoelastic pattern of thermal gelation and reduced the gel elasticity（G’）and viscosity（G"）.G’ of PSE-like meat had no similar peak during heating from 25 ℃ to 54 ℃,suggesting that PSE-like meat batter had higher protein denaturation and lowered gel forming ability.Heated PSE-like meat batter had lower textural characteristics（gel strength,hardness,springiness,cohesiveness,and chewiness）and water holding capacity（cooking loss,centrifugation loss and pressing loss）（P<0.05）,the gel strength was lowered 46%,hardness was lowered 40%,and cooking loss was higher about 7%.However,the difference in color was small when used in further products.In conclusion,PSE-like poultry meat changed the chemical composition and impaired protein functionality which is related to the lower SSP extraction and higher extent of protein denaturation.2.Changes in protein characteristic of PSE-like and normal chicken breast meat during processingIn order to explore mechanisms in the inferior functional properties of PSE-like chicken breast meat,the objectives of this study were to investigate SSP composition,protein thermal stability,water-protein interaction,microstructure,and protein conformation between PSE-like and normal chicken breast meat batters using differential scanning calorimetry,LF-NMR,SEM,and Raman spectroscopy.No significant changes were observed in the electrophoretic patterns of salt-soluble protein extracts by SDS-PAGE,suggesting not a specific protein alteration affecting the functional properties.Heated PSE-like meat batter formed an aggregated gel matrix,while normal meat batter produced a compact gel network with fine,cross-linked strands by many protein filaments.LF-NMR revealed an increase in the water mobility in heated PSE-like meat batter with an increasing amount of loosely bound water（P<0.05）.DSC showed that PSE-like meat had lower the thermal transition temperature（Td）and denaturation enthalpy（△H）of myosin and sarcoplasmic proteins/collagen（P<0.05）.In PSE-like meat,actin denaturation was particular evident after salt addition（P<0.05）,suggesting a general effect of proteins denaturations.Moreover,Raman spectroscopy indicated that PSE-like meat batter had less unfolded α-helix and β-sheet structure formation,reduced exposure of hydrophobic and tyrosine residues（P<0.05）,and changes in the microenvironment of aliphatic residues and tryptophan,which affected salt-soluble proteins extraction,gel properties,and water-holding capacity.In conclusion,the inferior functional properties of PSE-like meat were attributed to not only myosin denaturation,but also actin denaturation after salt addition and different protein structural states.3.Difference and mechanism of gel properties of actomyosin extracted from PSE-like and normal chicken breast meatActomyosin were extracted from normal and PSE-like chicken breast meat and the gel strength,water-holding capacity,protein loss,particle size and distribution,dynamic rheology and protein thermal stability were determined,then turbidity,active sulfhydryl group contents,hydrophobicity and molecular forces during heat-induced gelation were comparatively studied to explore the basis for the different functional properties of PSE-like and normal chicken breast meat after heat treatment.SDS-PAGE showed that patterns of actomyosin from PSE-like and normal meat were similar.PSE-like actomyosin gel had lower gel strength,water-holding capacity and increased protein loss after heat treatment（P<0.05）.Dynamic rheology showed that PSE-like actomyosin had different viscoelastic pattern of thermal gelation with normal actomyosin and reduced the gel elasticity（G’）and viscosity（G"）.The transition temperature of G’ from PSE-like actomyosin was lowered than that of normal actomyosin.Particle size of PSE-like actomyosin was lower than that of normal actomyosin（P<0.05）,and DSC showed that PSE-like meat had lower the onset temperature（To）and the thermal transition temperature（Td）.The turbidity of PSE-like actomyosin were higher in the range of 40℃-60℃,indicating protein aggregation was more intense.Reactive sulfhydryl group content increased and then decreased with increasing temperature.Hydrophobicity of PSE-like and normal actomyosin increased with increasing temperature.From 40℃to 60℃,the sulfhydryl group content and hydrophobicity of PSE-like actomyosin was significantly higher than that of normal actomyosin（P<0.05）,however,transtion from reactive sulfhydryl group into a disulfide bond was less than the normal actomyosin and hydrophobicity of PSE-like is significantly less than that of normal actomyosin at higher temperature.Molecular forces during heating showed that ionic and hydrogen bonds reduced with increasing temperature,the hydrophobilic interactions increased and then decreased.Hydrophobic force values mainly contributed to heated induced actomyosin gel.The formation of ionic and hydrogen bonds was very different significantly between PSE-like and normal actomyosin（P<0.05）while the differences of hydrophobilic interactions were not significant（P>0.05）.These differences in the formation of chemical group and intermolecular bonds possibly affected protein-protein interaction and contributed to diverse gelation properties and water-holding capacity between PSE-like and normal actomyosin.4.Use of high-intensity ultrasound to improve functional properties of batter suspensions prepared from PSE-like chicken breast meatIn order to explore novel processing for modifying the functional properties of pale,soft,exudative（PSE）-like chicken breast meat,we investigated the effects of high intensity ultrasound on the functional and rheological properties,particle size distribution,microstructure and protein secondary structures of PSE-like meat batter suspension.Normal and PSE-like chicken breast meat batter suspensions（7.5%meat proteins,2.0%salt,w/w）were prepared and treated by ultrasound for 0,3 or 6 min（frequency 20 kHz and amplitude 60%）.Ultrasound treatments had significantly increased pH,gel strength and water holding capacity of normal and PSE-like meat gels（P<0.05）.Ultrasound treatments altered the rheological behaviors of normal and PSE-like batter samples,which were accompanied with the increase of the elastic（G’）and viscous（G"）modulus.The microstructure of heated normal and PSE-like batter samples could form a compact and denser gel network after ultrasound treatments.Ultrasound treatments reduced the salt solubility of myosin as indicated by its intensity in SDS-PAGE.However,the particle size of ultrasound treated normal and PSE-like batter samples was reduced and become more uniform.Moreover,ultrasound treatments decreased the a-helical content and increased the formationβ-sheet,β-turns and unordered contents of normal and PSE-like meat proteins.These results suggest that high intensity ultrasound may be used to modify the functionality of PSE-like meat with the potential to increase economical benefits for the poultry industry.