Predicting colour and flavour stabilities of meat from pre-slaughter assessments

Summary

​To determine whether circulating levels of blood isoprostane can be utilised as an effective biomarker in prime lambs to predict changes in the colour and/or flavour stabilities of meat post-slaughter; the circulating level of blood isoprostane was determined in 84 lambs finished on four different finishing diets (lucerne, ryegrass, commercial feedlot ration and a combination of rye grass and commercial feedlot ration).  The circulating levels of isoprostane for each animal was then correlated with traditional meat quality measurements for colour and/or flavour stabilities.  This included lipid oxidation levels in meat (i.e. thiobarbituric acid reactive substances (TBARS) analysis), muscle vitamin E content and meat colour redness and brownness as determined by HunterLab.  
We found that lambs finished on ryegrass had the highest level of muscle vitamin E content, 2.9 mg/kg; whereas lambs finished on the commercial feedlot ration had the lowest muscle vitamin E content, 0.73 mg/kg (P < 0.001).  Lipid oxidation levels were lowest in lambs finished on the ryegrass diet, highest for lambs finished on the commercial feedlot ration and intermediate for lambs finished on lucerne and combination ration (P < 0.001).  After 8 weeks finishing, blood isoprostane levels were positively corelated with the level of lipid oxidation of fresh (5 days) and aged (60 days) meat displayed for 96 hours under simulated retail conditions (P < 0.01).  Also, there was negative linear relationship between isoprostane concentration and muscle vitamin E concentration (P < 0.07); and lipid oxidation and muscle vitamin E concentration (P < 0.001). 
Therefore, after 96 hours simulated retail display, lambs finished on a ryegrass contain muscle vitamin E concentrations that reduce lipid oxidation in both fresh and aged meat.  Whilst, lambs finished on a commercial feedlot ration have a significantly lower muscle vitamin E concentration that promoted greater levels of lipid oxidation in fresh and aged meat under the same conditions.  Increased levels of lipid oxidation post-farm gate influences the flavour/aroma of lamb and has a negative impact on the consumers eating experience.  However, we did not observe a significant relationship between the overall redness of meat stored under simulated retail display conditions at 1 and 4 days with blood isoprostane concentrations at week 0, 4, 6 or 8 of finishing or the vitamin E concentration of muscle.    
The overall results show great Industry promise and prove that blood isoprostane concentration can be used as a biomarker to predict oxidative stress in farm animals pre-farm gate.  Increased oxidative stress is associated with reduced meat quality and flavour deterioration in lamb due to higher levels of lipid oxidation.  This is the first known report to identify a link between a biomarker of oxidative stress (i.e. isoprostane concentration) and reduced meat quality in sheepmeat.