Date of Award
Master of Science (MS)
Y H Brad Kim
Y H Brad Kim
Committee Member 1
Committee Member 2
Postmortem aging has been extensively practiced in the meat industry for decades due to its beneficial impact on improving eating quality attributes. However, prolonged postmortem aging may adversely impact color and/or lipid oxidation stabilities of meat, leading to decreased display shelf-life and increased rancid off-flavor. As physical/biochemical changes occur during postmortem aging, metabolites that impart antioxidant or pro-oxidant activities are generated or consumed, which could be related to the oxidation stabilities of postmortem muscles with aging. However, the underlying mechanism of the aging-induced oxidation susceptibility has not been fully established. Therefore, the overall objective of this thesis was to understand the effect of postmortem aging on oxidation related metabolites in different bovine muscles.
The first chapter of this thesis is the literature review, and the second chapter focuses on determining the effect of postmortem aging on color and lipid oxidation stabilities in different bovine muscles. Three muscles, longissimus lumborum (LL), semimembranosus (SM), and psoas major(PM) were chosen (n=7) for the study due to the distinct features in muscle fiber composition, oxidation stabilities, and metabolic properties of those muscles. At 1-day postmortem, the three muscles were separated from 7 beef carcasses, divided into 3 sections, vacuum-packaged, and assigned to 9, 16, and 23 days of aging. After each aging time, steaks made from each sections were overwrap PVC-packaged and displayed for 7 days. Instrumental and sensory color characteristics were measured. Lipid oxidation by measuring TBARS and conjugated dienes (CD), myoglobin content, and non-heme iron contents were determined. Intensified discoloration and decreased redness of meat were observed with prolonged aging, where LL was the most color-stable followed by SM and PM (P
The third chapter of this thesis was a study to identify key metabolites that could be associated with oxidation stabilities of aged bovine muscles using metabolomics approach. Selected raw samples (n=4; at day 0 of display of each aging) from the previous study (Chapter 2) were analyzed using the HPLC-ESI-MS metabolomics. The metabolomics data were analyzed using PCA and split-plot ANOVA. Spearman correlations between metabolites and oxidation related quality attributes were conducted using R software. The metabolomics platform detected 1012 compounds, among which 243 were significantly responsive to either aging or muscle treatments. Most distinct metabolites being identified were carnitines, free amino acids, nucleotides, vitamins /coenzymes, and glucuronides. NAD showed a positive correlation to the redness of meat color (r = 0.672) and negative correlations to discoloration (r = -0.535), TBARS (r = -0.554), and non-heme iron (r = -0.667), indicating its relevance to myoglobin redox form stability and/or lipid oxidation stability. A group of carnitines that decreased with aging was associated with decreased redness (r = -0.67) and intensified discoloration (r = 0.70), which may be explained by their roles in the mitochondria matrix and/or their potential antioxidant properties. Glucuronides increased with extended aging and associated with discoloration (r = 0.56) and non-heme iron accumulation (r = 0.65). Some nucleotides, nucleosides and free amino acids were more liberated with aging and positively correlated to chemical/phenotypic oxidation indicators.
The results from the current study suggest that some metabolites could be associated with oxidation stabilities of beef muscles. In particular, our study confirmed the relevance of the NAD/NADH system in myoglobin redox stability. Further, we identified potential compounds, such as carnitines and glucuronides, which could be related to color/lipid oxidation stabilities of aged beef muscles. The identified key metabolites should be further investigated to reveal the chemical basis of oxidation stabilities of beef muscle and could be validated into biomarkers for industry to track the quality development of beef during aging.
Ma, Danyi, "Metabolomics Approach to Investigate Oxidation Stabilities In Different Bovine Muscles With Postmortem Aging" (2016). Open Access Theses. 957.