Metabolic profiling of the liquid core and solidified outer layer of preserved duck egg yolk using widely targeted metabolomics

Preserved duck egg yolk (PEY) gradually formed a distinctive liquid inner core (L-PEY) and solidified outer layer (S-PEY) during alkaline pickling. However, the distinctions in small molecule metabolites between these two regions have remained unclear. In this study, PEY, S-PEY, and L-PEY were extensively compared using widely focused metabolomics. The majority of the 596 metabolites found were fatty acyls (FAs) (14.4%), organic acids and their derivatives (12.9%), and amino acids and their metabolites (22.9%). The major classes, which combined accounted for 56.4%–79.1% of the total abundance, were glycerophospholipids (GPs), amino acids and their metabolites, and organic acids and their derivatives, according to relative quantitative abundance analysis. A total of 117, 47, and 169 differential abundance metabolites were identified in the comparisons of L-PEY vs. PEY, S-PEY vs. PEY, and L-PEY vs. S-PEY, respectively, mainly belonging to amino acids and their metabolites and FAs. GPs and amino acids were more abundant in L-PEY than in S-PEY, but FAs were significantly more abundant in S-PEY. Specifically, lysophospholipid (20:4/0:0), pyroglutamic acid, L-valine, lysine, and histidine were significantly more abundant in L-PEY, whereas free fatty acid (FFA) (22:5), FFA (20:2), and 12,13-epoxyoctadecenoic acid were significantly more abundant in S-PEY. These findings provide new insights into the metabolic basis of regional differentiation and quality formation in PEY.