# A preliminary nontargeted lipidomics analysis reveals greater acylcarnitine in dark-cutting beef longissimus lumborum across visual severity levels

## TL;DR

This study shows that dark-cutting beef has higher levels of acylcarnitine, suggesting changes in energy metabolism that lead to higher postmortem muscle pH.

## Contribution

The study provides new evidence linking acylcarnitine levels to altered energy metabolism in dark-cutting beef.

## Key findings

- Dark-cutting beef had significantly higher levels of acylcarnitine compared to normal-pH beef.
- Medium- and long-chain acylcarnitine levels were significantly different between dark-cutting and normal beef.
- Acylcarnitine species 20:2, 18:1, and 16:0 were the top contributors to differences between dark-cutting severities and normal steaks.

## Abstract

Dark-cutting beef continues to remain one of the challenges for the global beef industry. The objective of this study was to determine the impact of varying visual degrees of dark-cutting condition on the lipidome profiles of beef longissimus lumborum. Beef carcasses (n = 6/treatment; 24 total loins) were identified at the time of grading based on the visual severity of dark-cutting levels, and beef strip loins (longissimus lumborum) were collected from these carcasses following fabrication. Treatments included a normal, bright cherry-red control (pH = 5.54), shady dark-cutting (half dark; pH = 5.96), moderate dark-cutting (two-thirds dark; pH = 6.38), and moderately severe dark-cutting (full dark; pH = 6.55). Approximately after 48 to 60 h postmortem, two steaks were sliced off the anterior end of each loin. The first steak was used for bloom color analysis and the second steak was used for nontargeted lipidomoc analysis using a a liquid chromatography massspectrometry approach. A total of 379 lipids, representing different classes of lipids, were identified across the 4 treatments. Pairwise comparisons revealed 21, 22, and 23 lipid species that differed (P < 0.05) in shady, moderate, and moderately severe dark-cutting beef, respectively, compared with normal beef. Only one lipid species (acylcarnitine 22:2) differed between moderately severe and moderate groups. Acylcarnitine species of varying carbons and saturations were the most common of the shared species in dark-cutting samples. Medium- and long-chain acylcarnitine levels were significantly different (P < 0.05) between dark-cutting treatments and normal pH. The importance projection analysis indicated that acylcarnitine 20:2, 18:1, and 16:0 were the top 3 lipid species contributing to differences between dark-cutting severities and normal steaks. The relative proportion of lipids involved in energy metabolism was greater (P < 0.05) in moderate and moderately severe than in normal bright red steaks. Greater acylcarnitine levels in postmortem muscle suggest mobilization of fatty acids for energy homeostasis in dark-cutting beef and altered metabolism.

Dark-cutting beef has more acylcarnitine than normal-pH beef. The current study offers further evidence that changes in energy metabolism result in high postmortem muscle pH and dark-cutting beef.