| Postmortem aging is the key method to improve the ediable quality of beef.The physical and chemical properties of muscle will change to varying degrees during aging.Appropriate aging time can improve the quality and palatability of meat.However,great aging time will lead to negative effects on the quality of meat,such as excessive oxidation and shortening shelf life.Wet-aging is the most widely used method in the post-mortem aging process.The exudate will gradually increase with the extension of wet-aging time.The "natural juice" exuded from muscle tissue can reflect some information of meat to a certain extent,but it usually be discarded directly,and very few studies have been performed to investigate the exudate itself and its relationship with meat quality.Therefore,in the present study,the longissimus muscle of cattle was selected as the research object to clarify the changes of beef quality and oxidative stability during wet-aging,analyze the color,clarity,lipid and protein oxidation changes of tissue exudate during wet-aging,and reveal the proteome differences of tissue exudate during wet-aging by label-free proteomics technology.The final objective is to screen out the characteristic proteins which can be used to monitor the aging process in the later stage or partly predict and evaluate the meat quality.The main results of this paper are as follows:(1)The p H,water content,tenderness,lipid and protein oxidation of longissimus dorsi muscle during postmortem wet-aging(3,7,14,21,and 28 d),as well as the color changes of aged beef during simulated retail display were analyzed.Beef p H increased with aging(P<0.05)from 5.49 in 3 d to 5.57 and 5.61 in 21 and 28 d,respectively.The purge loss increased gradually during ripening(P<0.05),and there was no significant change in centrifugation loss,cooking loss and drip loss.The maximum shear force value of beef was 4.09 kg at 3 days of aging,which decreased significantly(P<0.05)to 3.01 kg at 28 days of aging.The myofibril fragmentation index increased significantly with aging(P<0.05),from 42 at 3 days to 78 at 28 days.The tenderness of beef was significantly improved.However,the thiobarbituric reactive substances(TBARS)of beef increased significantly(P<0.05)with aging,which indicated the more severe lipid oxidation after extended aging treatments.The carbonyl value of beef increased significantly(P<0.05),while sulfhydryl content decreased significantly(P<0.05)during aging,which suggested the increased protein oxidation after aging treatments.The effects of wet-aging on color stabilities of beef during retail display were investigated,and the results indicated that extended aging duration was detrimental to beef color stability during subsequent retail display,which reflected by the more significant decreased redness value(a*)and chroma in greater aging time(21and 28 d groups)during display duration.(2)The clarity,absorbance of A680 nm,color,TBARS value,carbonyl value and sulfhydryl content of beef tissue exudate changed significantly with aging.During aging,the clear and transparent exudate gradually changed into turbid and dark red,and the absorbance value at 680 nm significantly increased(P < 0.05).The L*,a* and b* value of exudate increased significantly.The TBARS value of exudate increased significantly from 0.17 mg/kg on 3 d to 0.52 mg/kg on 28 d(P < 0.05).Meanwhile,the carbonyl value of exudate increased significantly(P < 0.05),and the sulfhydryl content decreased significantly(P < 0.05)with aging,indicating the increased degree of protein oxidation.The changes trend of basic physical and chemical indexes of exudate was basically consistented with that of meat quality results.(3)The proteome changes of beef exudate during wet-aging were detected by label-free proteomics.The results showed that a total of 1023 proteins were detected in the exudate,and 77% of the proteins had a molecular weight lower than 70 k Da.A total of 130 proteins changed significantly with aging(P < 0.05),and most of them gradually accumulated in the exudate.Pearson's correlation analysis results showed that 74 proteins were significantly correlated(correlation coefficient > 0.6 and P <0.05)with at least one quality attribute,including 17 enzymes involved in metabolism,4 heat shock proteins,29 structural proteins and 12 other proteins.Combined with the variable projection importance(VIP value)> 1 of partial least squares regression discriminant analysis(PLS-DA),a total of 15 potential proteins that can be selected as a source of potential biomarkers to indirectly reflect meat quality changes during wet-aging processing. |
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