Metabolomic insights into the aging process of <i>Citrus reticulata</i> 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.