81 Evaluating the metabolome of beef carcasses with varied Longissimus lumborum color

Abstract Beef carcasses with non-normal color costs the United States industry billions of dollars annually. While dark cutters have long been attributed to long-term stress and glycogen depletion, few studies have aimed to understand other potential metabolomic markers of dark and light-colored beef. The objective of this study was to determine the metabolomic profile of carcasses possessing dark, intermediate, normal, and light lean according to RGB instrumental color evaluation. Over 9 consecutive months, 216 carcasses (n = 24/mo) from 4 color categories were collected from 2 commercial abattoirs. Carcasses were identified using L* values from industry grading cameras. Carcasses were classified into categories based on the least L* value from either side: dark (L* ≤ 55; n = 53), intermediate (55 L* 60; n = 54), normal (60 ≤ L* 80; n = 54), or light (L* ≥ 80; n = 54). A 5.08 cm steak was collected from the longissimus lumborum from both carcass sides. Steaks were aged until 5 d postmortem, snap-frozen and homogenized into a powder. Metabolites were extracted by weighing 50 mg of sample into a tube with 50 μL of ribitol and 1.5 mL of 80% methanol and homogenized using a bead beater. Sample extract was dried with nitrogen gas before being reconstituted with 50 μL of methoxyamine hydrochloride and 50 μL of N-methyl-N-trimethylsilyltrifluoroacetamide with 1% trimethylchlorosilane. Untargeted metabolomics was conducted via gas chromatography-mass spectrometry. Mass spectral data were deconvoluted, aligned, and annotated using MS-DIAL. Total ion counts were normalized by the internal standard and log10 transformed prior to analysis. Data were analyzed using MetaboAnalyst by analysis of variance. Pathway analyses were conducted using the KEGG Bos taurus pathway library. Significance for all analyses was declared at FDR P 0.05. Metabolite analyses identified 137 total features with 74 identified by the reference library and 45 were differentially expressed between carcass color categories. Malic acid was greatest in dark carcasses and least in normal and light carcasses (FDR P 0.05). 1-methylgalactose, beta-D-galactose, sorbose, and phosphohexonoic acid was greatest in light carcasses, second in normal, third in intermediate, and least in dark carcasses (FDR P 0.05). Methyl O-D-galactopyranoside, L-iditol, D-fructose-phosphate, and D-sorbitol 6-phosphate were greatest in light, intermediate in normal and intermediate, and least in dark carcasses (FDR P 0.05). Uridine 5-diphospho-N-actetylglucosamine was greatest in light and normal and least in dark carcasses (FDR P 0.05). Pathway analyses identified the pentose phosphate pathway, galactose metabolism, neomycin, kanamycin, and gentamycin biosynthesis, and valine, leucine, and isoleucine biosynthesis as the likely metabolic pathways causing differences (FDR P 0.05) between carcass color categories. These results identify metabolites of interests and pathways that may contribute to variation in beef color and indicate that differences within beef carcass color is a multifactorial problem centered around energy and protein metabolism.