The effect of rigor temperature, ageing and display time on the quality of hot boned beef semimembranosus muscle
|dc.contributor.advisor||Birch, John Edward|
|dc.contributor.advisor||Bekhit, Alaa El Din Ahmed|
|dc.contributor.author||Mungure, Tanyaradzwa Emmanuel|
|dc.identifier.citation||Mungure, T. E. (2015). The effect of rigor temperature, ageing and display time on the quality of hot boned beef semimembranosus muscle (Thesis, Master of Science). University of Otago. Retrieved from http://hdl.handle.net/10523/6074||en|
|dc.description.abstract||Lipid oxidation is a primary mechanism that causes a decrease in meat quality. Abundant research has been done on the eating and keeping quality attributes of beef as affected by rigor temperature, but limited work has been done on monitoring the changes of unsaturated fatty acids during rigor attainment, ageing and display time due to oxidation and overall lipid oxidative stability. This study uses a novel technique of 1H NMR to monitor lipid oxidation and analyse CLA (Conjugated Linoleic Acid) and cholesterol oxidative stability. These techniques, with further investigation and research, may have commercial application in monitoring beef lipid quality deterioration. The objective of this research was to study the effects of rigor temperature, ageing and display time on meat quality and lipid oxidative stability of hot boned beef semimembranosus muscle. The manipulation of muscles’ rigor temperature has been largely restricted to longissimus et lumborum due to its commercial importance compared to the other metabolically different muscles. Six topsides (semimembranosus, SM) were removed from 6 carcasses within 45 min post-mortem following electrical stimulation of the carcasses under commercial processing conditions. The SM muscles had an average weight of 27.5 ± 4.1 kg. Muscles from the right and left topsides of each animal were divided into 2 samples resulting in 4 samples obtained from each animal. To ensure equal distribution over the 4 treatments, samples were randomised. The samples were packed into labelled plastic bags and transferred into 5°C, 15°C, 20°C or 25°C incubators until attainment of rigor mortis. Following rigor attainment each sample was cut into 4 pieces, weighed, vacuumed packed, randomly assigned to 4 different storage times (3, 7, 14 and 21 days) and stored at 4°C until the desired ageing time was reached. Samples were displayed for 7 days under light and aerobic conditions at 4°C. As rigor temperature increased, the attainment of rigor mortis was hastened and the ultimate pH reduced (5.69 for 5°C and 5.50 for 25°C). Ageing the meat (from day 3 to 14) increased the pH. This is likely due to increased proteolysis of muscle proteins leading to increased free amino acids and dipeptides (p < 0.01). Electrical conductivity increased as the rigor temperature increased (p < 0.001). Tenderness, one of the most important meat quality attributes, was not affected by rigor temperature (p = 0.24). Although rigor temperature had no statistically significant effect on tenderness, the 15°C treated samples were determined to be the most tender of all treatments. Ageing meat had a positive impact on meat tenderness (p < 0.01). Tenderness increased with ageing time due to myofibrillar protein degradation by endogenous proteases. Mean shear force decreased by an average of 25 N from day 3 to day 21 ageing time. Colour was affected by rigor temperature; lightness (L*) increased with a rise in rigor temperature (p = 0.012). Ageing also increased the L* values (p < 0.01); this was attributed to protein structure modification that enabled higher reflection of light due to reduced water holding capacity. Display time had a negative effect on L* values (p < 0.01). Redness (a*) increased with rigor temperature (p = 0.027). Ageing and display time, however had a negative impact on a* values caused by increased metmyoglobin accumulation with time. Yellowness (b*), was not affected by rigor temperature. Yellowness decreased with both ageing and display time (p < 0.01). Thiobarbituric acid reactive substances (TBARS values), which measure the formation of secondary lipid oxidation products, were not affected by rigor temperature (p > 0.05). TBARS increased with ageing and display time (p < 0.01). Over the ageing period, endogenous antioxidants were depleted and over the display period, the aerobic conditions cause production of secondary oxidation products accounting for this increase. Changes in aliphatic to diallylmethylene proton ratio (Rad), aliphatic to olefinic proton ratio (Rao) and olefinic proton moles allow the monitoring of lipid oxidation by 1H NMR. Rigor temperature did not have an effect on Rad, Rao and olefinic proton moles (p > 0.05). Rad ratios increased with ageing time, and further increased with display time (p < 0.05). The increase in Rao was not as rapid and sensitive to change as Rad because the olefinic proton signals emanate from monounsaturated fatty acids (MUFAs) which are not as readily oxidised as the diallylmethylene proton from polyunsaturated fatty acids (PUFAs) used in the Rad. The olefinic proton moles declined with display time (p < 0.05). The small change in number of olefinic proton moles illustrated the low loss/oxidation of monounsaturated fatty acids (MUFAs) during the treatments. The polyunsaturated fatty acid (PUFA) content determined by GC–FID showed a decline with ageing and display time, supporting the oxidation observed by Rad and Rao. The rapid technique of absolute quantitation by 1H NMR was used for CLA analysis and the correlation determined with GC-FID analysis of FAMEs (R2=0.9682). The beef SM samples had a CLA content ranging from 2.1 to 4.3 mg/g lipid. CLA oxidative stability was not affected by rigor temperature, ageing and display time (p > 0.05) showing high stability and low susceptibility to oxidation. The beef samples contained high cholesterol levels ranging between 60-90 mg/100g of muscle compared to other previous studies on beef. Rigor temperature had no effect on cholesterol oxidative stability; however, stability did decline with ageing time. Cholesterol concentration declined significantly with display time (p < 0.01). 7α &β-Hydroxycholesterol (7α-β-HC) and 7-ketocholesterol (7-KC) were the cholesterol oxidation products (COPs) that were positively identified. Rigor temperature did not have an effect on their production (p > 0.05); however they increased with ageing and display time (p < 0.05).|
|dc.publisher||University of Otago|
|dc.rights||All items in OUR Archive are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.|
|dc.title||The effect of rigor temperature, ageing and display time on the quality of hot boned beef semimembranosus muscle|
|thesis.degree.name||Master of Science|
|thesis.degree.grantor||University of Otago|
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