| Pale,soft,exudative(PSE)-like chicken meat has been a significant meat quality defect in the poultry industry,which affects the sensory qualities and impairs the functional properties when used in further processed meat products.It had a significantly lower salt-soluble protein extraction,led to the decreaing in the cooking yield and impaired the inferior textural characteristics of processed meat products,thus resulting in more economic loss to the poultry industry.As a kind of isoelectric solubilization/precipitation method,PSE-like chicken protein isolate was extracted by sequential alkali dissolution and acid precipitation.However,PSE-like chicken protein isolate had inferior functional properties when it was recovered by acid precipitation at p H 5.5,and the extraction rate were still further improved.Therefore,this study firstly used the ultrasound technology to inverstigate its effect on the structure and emulsifying properties of PSE-like protein isolates.Then,the effect of UAE on the extraction rate and functional properties of PSE-like protein isolate were determined,and the mechanism of influence on the stability of the emulsion was further understood from the protein structure and interface properties.Finally,the fluorescence quenching spectrum analysis and EGCG stability measruemenet were used to compare the protective effect of PSE-like protein isolates obtained by different ultrasound methods on EGCG,in order to provide theoretical reference and technical support for the processing and utilization of PSE-like chicken protein isolates.The specific contents and results are as follows:(1)The effects of different ultrasound power levels(0,150,300 and 450 W)on the structure and emulsifying properties of PSE-like protein isolate as well as the correlation between them were analyzed.The results showed that the particle size and the absolute value of zeta potential of the protein isolate were decreased significantly(P<0.05)with the increase in ultrasonic power,and the particle size distribution gradually changed from bimodal to unimodal distribution;protein composition was not obviously changed,while the band intensity of myosin heavy chain and actin were generally increased.The relative contents of ?-helix and random coils were increased significantly,and the relative contents of ?-sheet and ?-turn were reduced.The content of free sulfhydryl groups,surface hydrophobicity and fluorescence intensity was increased obviously.Scanning electron microscopy(SEM)further confirmed that ultrasound treatment changed the structure of the protein isolate and reduced its particle size.After ultrasonic treatment,the solubility,emulsifying activity,and emulsifying stability of the protein isolate were significantly improved by 1.17 times,10.29% and 2.63 times,respectively(P<0.05).Meanwhile,correlation analysis and principal component analysis(PCA)showed that there was a high correlation between the improvement in the emulsifying properties of the protein isolates and its structural changes after ultrasound treatment.In summary,ultrasound treatment can change the structure of PSE-like protein isolate and improve its emulsifying properties.(2)The effects of ultrasound assisted alkali extraction(UAE)(ultrasound time of 0,5,10,and 15 min)on the extraction rate and functional properties of PSE-like protein isolates were studied.The results showed that the yield of PSE-like protein isolates with ultrasound treatment was significantly increased relative to the control without ultrasound treatment(68.58% versus45.55%)(P<0.05),and that the protein content was significantly increased by 25.32%(P<0.05)compared with the control group.The proteins obtained at 10 min of UAE had low turbidity,viscosity and particle size.SEM further confirmed that the structure of the proteins extracted by UAE was looser with smaller fragments compared with the control group.The cooking loss of heat-induced gels from the ultrasonically extracted proteins was significantly reduced by 61.77% compared with that from the control group(P<0.05),indicating that the former had higher water retention capacity than the latter,whereas the gel strength of the former was significantly lower than that of the latter(P<0.05).In addition,the solubility,emulsifying activity and emulsion stability of the ultrasonically extracted proteins were increased by 38.56%,20.25% and 5.59% in comparison with those of the control group,respectively.In conclusion,UAE not only increased the purity of proteins recovered from PSE-like chicken meat,but also improved the functional characteristics of the proteins.(3)In order to further elucidate the mechanism of UAE on the stability of PSE-like protein isolate prepared emulsion,the effect of UAE(ultrasound time: 0,5,10 and 15 min)on the structural properties,interface properties and emulsion properties of PSE-like protein isolate was studied.The results showed that UAE had no effect on the composition of the PSE-like isolates,however,the secondary and tertiary structures of the PSE-like isolates was changed,manifested as increased content of ?-helix and ?-turn,?-sheet and random coil content decreased,indicating that UAE promoted the unfolding of the protein structure.The PSE-like protein isolate after UAE prepared emulsion has lower interfacial tension and more uniform distribution.In addition,Raman spectroscopy showed that the protein order structure(?-helix and ?-sheet)in the emulsion after UAE increased,which was favorable for the formation of a more stable emulsion.Finally,the PSE-like protein isolate were treated with different ultrasound methods(control group: unsound group;ultrasound group: 450 W,5 min;ultrasound-assisted extraction group: 450 W,10 min),the protective effect of EGCG was investigated by fluorescence quenching spectroscopy and UV absorption.The fluorescence quenching spectrum showed that the protein isolate for UAE group had the strongest binding ability to EGCG,and the number of binding sites was the largest(1.265),and the control group,ultrasound group and UAE group could all protect the degradation of EGCG,and UAE had the best protection effect. |
PDF Full Text Request