Distinct Preservation Strategies of Red and Yellow Onions Under Low-Temperature Storage Revealed by Integrated Metabolomics

The effects of ambient storage (A), cold storage (C), and frozen storage (F) on the quality, metabolomic characteristics, and sulfur-related aroma of red onion ‘Kewei Red 10’ (R10) and yellow onion ‘Kewei Yellow 14’ (Y14) were investigated using integrated non-targeted and volatile metabolomics. Ambient storage accelerated shrinkage, firmness loss, and sensory deterioration in both cultivars, whereas low-temperature storage effectively delayed quality decline. R10 exhibited better tolerance to frozen storage, while Y14 performed better under cold storage. Metabolomic analysis revealed that amino acids and lipid-related metabolites were closely associated with onion senescence in both cultivars. In contrast, flavonoids were enriched in preservation-associated subclasses in R10, whereas organic acids and their derivatives were more strongly associated with delayed senescence in Y14. Volatile metabolomic analysis identified sulfur compounds and heterocyclic sulfur compounds as the major contributors to onion aroma. Sulfur-related volatiles showed distinct cultivar-dependent accumulation patterns, with many sulfur compounds accumulating prominently in ambient-stored R10-A, whereas cold-stored Y14-C maintained relatively higher levels of characteristic onion-like aroma compounds. These findings demonstrate distinct metabolic adaptation strategies between red and yellow onions during storage and suggest that cultivar-specific storage conditions are required to optimize both shelf life and flavor quality.