Exploring the Lipids Involved in the Formation of Characteristic Lactones in Japanese Black Cattle

The meat from Japanese Black cattle (Japanese Wagyu) is finely marbled and exhibits a rich and sweet aroma known as Wagyu beef aroma. To clarify the key metabolites involved in the aroma, we analyzed the correlation between lactone and lipid composition in Japanese Black cattle. Using gas chromatography-olfactometry, we identified 39 characteristic odorants of the intermuscular fat. Seven characteristic lactones considered to be involved in Wagyu beef aroma were quantified and compared in the marbled area and intermuscular fat using a stable isotope dilution assay. Among them, γ-hexalactone was the only lactone whose level was significantly higher in the marbled area. To explore the lipid species involved in lactone formation, we analyzed samples with different aroma characteristics. Liquid chromatography-mass spectrometry revealed eight lipid classes and showed significant differences in triacylglycerides (TAGs). To determine the molecular species of TAGs, we performed high-performance liquid chromatography analysis and identified 14 TAG species. However, these analyses showed that seven lactones had a low correlation with the TAGs. However, γ-hexalactone showed a positive correlation with linoleic acid. This study suggests that lipid composition affects the characteristic lactone profile involved in the Wagyu beef aroma.

Synthesis and maintenance of lipid droplets are essential for mouse preimplantation embryonic development

Lipid droplets (LDs), which are ubiquitous organelles consisting of a neutral lipid core coated with a phospholipid monolayer, play key roles in the regulation of cellular lipid metabolism. Although it is well known that mammalian oocytes and embryos contain LDs and that the amount of LDs varies among animal species, their physiological functions remain unclear. In this study, we have developed a method based on two-step centrifugation for efficient removal of almost all LDs from mouse MII oocytes (delipidation). We found that delipidated MII oocytes could be fertilized in vitro, and developed normally to the blastocyst stage even when the embryos were cultured in the absence of a fatty acid supply. LDs were newly synthesized and accumulated soon after delipidation, but chemical inhibition of long chain acyl-CoA synthetases (ACSLs) blocked this process, resulting in severe impairment of early embryonic development. Furthermore, we found that overabundance of LDs is detrimental to early embryonic development. Our findings demonstrate the importance of synthesis and maintenance of LDs, mediated in part by ACSL activity, during preimplantation embryonic development.