Metabolomic insights into the aging process of Citrus reticulata cv. ‘Dahongpao’ peel

This study investigated the changes in the volatile metabolome of C. reticulata cv. “Dahongpao” (Chuanchenpi) after aging for 1, 2, and 3 y. Using Headspace Solid-Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry, we analyzed Chenpi samples aged for 1 (CR1), 2 (CR2), and 3 (CR3) years. A total of 782 distinct volatile metabolites were provisionally identified, with terpenoids (28.52%), esters (14.45%), ketones (9.97%), heterocyclic compounds (8.44%), and alcohols (8.18%) being the predominant classes. Multivariate statistical analyses (PCA and OPLS-DA) revealed clear differentiation in volatile profiles among the three aging groups. Comparative analysis showed a net decrease in volatiles from CR1 to CR2, but a significant net up-accumulation of diverse compounds from CR1 to CR3, and particularly from CR2 to CR3. The 3 y Chenpi exhibited the most complex and enriched volatile signature, characterized by significantly higher levels of specific terpenoids (bicyclo[3.1.1]hept-3-en-2-one, 4,6,6-trimethyl-; 2-methyl-6-methyleneocta-2,7-dien-4-one), phenols (phenol, 2-propyl-), aldehydes (2-nonenal (Z)), and unique nitrogen (acetonitrile, 2,2’-iminobis-) and sulfur-containing compounds. KEGG pathway analysis highlighted significant enrichment in secondary metabolite biosynthesis, especially terpenoid pathways, which intensified with aging. These findings demostrate that 3 y of aging substantially enhances the aromatic complexity of Dahongpao Chenpi, offering strategies for quality standards, processing, and industrial application.