Influence Of Lipid Oxidation On Beef Colour Stability

Colour is one of the important meat quality indicators that is used by consumers to evaluate meat freshness.Oxidative reactions in meat are the most important factor in quality losses.The oxidation reaction leads to changes in colour pigments and lipids.In order to better understand the influence of lipid oxidation on beef colour stability,the relationship between lipid oxidation and colour stability was determined through four studies.The effect of beef lipid oxidation and colour stability under modified atmosphere packaging?MAP,80%O₂,20%CO₂?and vacuum package during ageing and display in air was investigated.The results showed that vacuum packaging maintained higher a^*values on the 7,14,and 21 days of ageing and lower L^*values on the 14 and 21 days of ageing compared to MAP?p<0.05?.Lower a^*values were observed on sample packed in MAP compared to vacuum packaging after 14 days of ageing time during day 2 and 4 of display and after 21 days of ageing time during day 2,4 and 6 of display.Significant differences?p<0.05?in TBARS were observed between MAP and vacuum during ageing time.Lipid oxidation was observed mainly in samples packed in MAP compared to vacuum,and positively correlated with results on colour stability.The effect of lipid oxidation secondary byproduct MDA on oxymyoglobin?OxyMb?during incubation in vitro was determined.MDA was combined with OxyMb at pH 7.4,37°C,and pH 5.6,4°C.No significant differences?p>0.05?was observed in MetMb formation in both condition in control and in the presence of MDA at the starting point of incubation 0 h.However,differences were observed during 3,4,24 and 48 hours of incubation time?p<0.05?.This research indicates that MDA may influence the oxidation of OxyMb to MetMb in vitro.The effect of lipid oxidation product HNE on oxymyoglobin?OxyMb?oxidation during incubation in vitro was determined.HNE was combined with OxyMb at pH 7.4,37°C,and pH 5.6,4°C.Results showed that MetMb formation percentage increased during 0,3,and 4 h of incubation time in control and HNE treatment at pH 7.4,37°C.MetMb formation percentage increased during incubation time in controls and in the presence of HNE at pH 5.6,4°C.Significant differences?p<0.05?were observed in MetMb formation in both condition at pH 7.4,37°C and pH 5.6,4°C in control and in the presence of HNE at 0 h of incubation time.An interaction between treatments and conditions of the treatment was observed on OxyMb formation?p<0.05?.Some inconsistent results of the influence of HNE on the oxidation of OxyMb to MetMb formation have been found during incubation.Our results suggest that HNE may influence the oxidation of OxyMb to MetMb formation in vitro.In conclusion the variation of colour stability may be induced by lipid oxidation.More studies should be done deeply to understand the mechanism of variation of meat colour stability.The effect of MDA on beef colour stability was investigated.Beef longissimus lumborum muscle samples from five animals were cut into 2 cm thick to examine the effect of injection of MDA on colour stability.Treatments were formulated to contain 0.1,0.2 and 0.3 mg of MDA/100 g of meat with a control group.Samples were overwrapped and kept at 4°C for 1,2,3,4 and 5 days.After each ageing time,colour stability,lipid oxidation and metmyoglobin formation were determined.The results revealed that no differences were observed among control group and low,medium and high MDA concentration groups?p>0.05?in coordinates L^*,a^*and b^*during ageing.Lipid oxidation analysis showed a significance difference?p<0.05?in TBARS on day 1 and day 2 of ageing between control group,low and high MDA concentration group.The results indicate that MDA after injection into the muscle did not influenced colour attributes of the fresh beef during ageing directly.