Abstract: To elucidate the differences in quality between egg yolks from different origins, this study employed metabolomics based on ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and gas chromatography (GC) to analyze the metabolite composition of egg yolks from Rongde Xiaohei chicken (RDY), a newly developed breed, and Beijing You chicken (BJY). The results indicated no significant differences between the two breeds in terms of egg shape index, eggshell strength, egg mass, Haugh unit, eggshell thickness, yolk mass, crude protein, or crude fat contents. A total of 293 differential metabolites were identified between RDY and BJY. The metabolite with the highest variable importance in projection (VIP) value was pepperolactam A (P < 0.05), suggesting its potential as a biomarker for distinguishing between the two egg yolks. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed five significantly enriched metabolic pathways: glycerophospholipid metabolism, linoleic acid metabolism, α-linolenic acid metabolism, glycerolipid metabolism, and arachidonic acid metabolism. These pathways influenced the types and contents of fatty acids through metabolic pathway overlap, signal transduction, and energy metabolism. In the glycerolipid and glycerophospholipid metabolic pathways, the upregulation of 1,2-distearoyl-sn-glycero-3-phosphocholine (PA) promoted the accumulation of myristic acid, oleic acid, palmitic acid, and neurogenic acid, whose contents were significantly higher in RDY than in BJY (P < 0.05). In contrast, the upregulation of PA in the glycerophospholipid pathway led to preferential utilization of stearic acid in phospholipid synthesis, thereby reducing its accumulation; with RDY exhibiting significantly lower levels of stearic acid than BJY (P < 0.05). Additionally, RDY contained significantly lower levels of linoleic acid than did BJY (P < 0.05). As a substrate in the linoleic acid metabolism pathway, the decreased content of linoleic acid led to downregulation of 9(S)-hydroxy-octadecadienoic acid (9(S)-HODE) in RDY. This study provides data support for the development of specialty egg brands and traceability systems in Hebei province.

Key words: egg yolk, metabolomics, ultra-high performance liquid chromatography-tandem mass spectrometry, gas chromatography, Kyoto Encyclopedia of Genes and Genomes pathway analysis