Dietary Modulation on sn-Position Distribution and Its Impact on Emulsifying and Nutritional Properties in Egg Yolk Lipids

Eggs are recognized as nutrient-dense foods, and precise modulation of yolk lipid structures is critical for enhancing their functional properties. In this study, laying hens fed with three different diets of corn-dried distiller grains with solubles (DDGS), whole grains and flaxseed, respectively, were chosen to investigate how dietary composition remodeled and modulate structures as well as functional properties of yolks. A multi-scale approach integrating GC-MS, MALDI-TOF-MS, and ¹ H NMR was applied. The results showed that yolks from hens fed with the DDGS diet contained trans-oleic acid (C18:1n9t) and palmitic acid (C16:0). The high level of monounsaturated fatty acids (MUFA) was found to improve the flexibility of the lipoprotein interface, thereby enhancing emulsifying activity. The cholesterol content in egg yolks was determined to be the lowest (0.84 mg/g) in the whole-grain diet, but an accumulation of phosphatidylserine was observed, which may disrupt the ω-6/ω-3 balance and increase the risk of oxidation. In yolks from the flaxseed diet, the docosahexaenoic acid (DHA) was preferentially deposited at the sn-2 position of triacylglycerols, promoting higher bioavailability of long-chain polyunsaturated fatty acids. The causal mechanisms underlying the differential regulation of yolk functionality by dietary components were elucidated. This was achieved through the specific remodeling of lipid molecular structures, which included the sn-2 positional distribution of fatty acids and variations in phospholipid subclasses. It aims to provide a novel integrated approach for the design of “phenomenon-substance-mechanism” on eggs via precision dietary formulation, further promoting a transformation of the poultry egg industry from compositional modification to structural empowerment.