Spatial metabolomics, LC-MS and RNA-Seq reveal the effect of red and white muscle on rabbit meat flavor

Meat quality is a key factor influencing consumer purchasing decisions. Muscle composition consists of various types of myofibers (type I and type IIa, IIb, IIx myofibers), and the relative composition of fiber types has a significant impact on the overall biochemical properties and flavor of fresh meat. However, the relationship between biochemical changes in myofibers and their impact on meat quality remains underexplored. In this study, we compared the differences in meat quality by examining different muscles in rabbits, each containing different muscle fiber types. We focused on the adductor (ADD) and semitendinosus (ST) as our research subjects and investigated skeletal muscle metabolism at the individual myofibers level using Spatial metabolomics. Additionally, we utilized LC-MS and RNA-Seq to explore the molecular mechanisms underlying the metabolic differences between red and white muscle fibers. Our findings demonstrated that variations in myofiber composition significantly influenced meat color, pH, water content, and drip loss. Spatial metabolomics analysis identified 22 unique red and white muscle fingerprint metabolites, while LC-MS analysis revealed 123 differential metabolites, and these differential metabolites were mainly enriched in the pathways of ABC transporters, Biosynthesis of amino acids, glutathione metabolism, and arginine biosynthesis. To further elucidate the molecular mechanism of differential metabolism in ADD and ST, we identified 2248 differentially expressed genes (DEGs) by RNA-Seq and then combined DEGs with DMs for joint analysis. We found that red muscle exhibited higher levels of metabolites such as L-glutamic acid, glutathione, ascorbate, ornithine, oxidized glutathione, gamma-L-glutamyl-L-cysteine, cysteinylglycine, fumaric acid, gamma-aminobutyric acid. Additionally, related metabolic genes such as MGST1, ODC1, MGST3 and PRDX6 were highly expressed in ST muscle. These metabolites and genes were enriched in the glutathione and nicotinamide pathways, and had significant effects on meat color and drip loss. Moreover, red muscle contained more flavor compounds and nutrients, including adenosine monophosphate (AMP), ornithine, citrulline, taurine, acetyl phosphate, L-glutamic acid metabolites, as well as taurine and hypotaurine metabolites. Our results demonstrate that fresh meat with a higher proportion of red muscle fibers exhibited superior meat quality, enhanced flavor, and higher nutrient content. Furthermore, red muscle contains more antioxidant metabolites that can effectively prevent meat oxidation during the production process.