HS-SPME/GC-MS and metabolomics elucidate volatile metabolite formation during fermentation of egg yolks

Egg yolk is a nutritionally rich and functionally excellent ingredient, but its undesirable flavor often limits its applications. To address this, we investigated lactic acid bacteria (LAB) fermentation as a sustainable strategy to enhance yolk flavor. Results show that among ten LAB strains, Limosilactobacillus reuteri and Lacticaseibacillus rhamnosus provided the highest odor acceptability for yolks and grew well throughout 3.5 h of fermentation. Fermented yolks contained 42.8-207 times higher concentrations of volatile compounds (including aldehydes and ketones) than control samples, enhancing buttery, creamy, floral, and apple-like aromas. Acetaldehyde level positively correlated with odor acceptance scores. Fatty acid metabolism was the primary pathway for generating methyl ketones, while amino acid and carbohydrate catabolism were the main pathways for synthesizing aldehydes, acids, and esters. This study demonstrates the potential of LAB fermentation to improve yolk flavor and provides insights for future research on regulating the flavor release during yolk fermentation.