Volatilomic Signatures and Antioxidant Activities of red Mandarin ( Citrus reticulata ‘Dahongpao’) Essential Oils from Peel, Flower, and Leaf

Abstract

Objective Citrus reticulata cv. ‘Dahongpao’ is an ancient Chinese cultivar whose by-products, peel, flower, and leaf remain underexplored. This study aimed to conduct a comprehensive comparative characterization of the volatilomic profiles, odor-active signatures, and antioxidant activities of the essential oils (EOs) extracted from these three tissues to establish a scientific basis for their differentiated valorization. Methods Essential oils were obtained from the three tissues using ultrasound-assisted hydrodistillation. The volatile metabolomes were analyzed using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. Antioxidant capacities were evaluated using spectrophotometric assays to determine total phenolic content, ferric reducing antioxidant power, and scavenging activities against superoxide and hydroxyl radicals. Results A total of 985 volatile metabolites were identified, dominated by terpenoids (25.99%), esters (15.63%), and heterocyclic compounds (9.44%). Tissue-specific chemical signatures were observed: peel EOs were enriched in terpenoids such as α-citral and (1α,3β,4β)-p-menthane-3,8-diol; flower EOs accumulated oxygenated monoterpene like linalool and nerolidol; leaf EOs were characterized by green-note aldehydes and alcohols, including (Z)-3-hexen-1-ol and phytol. Antioxidant profiling revealed functional divergence: leaf EO showed the highest superoxide scavenging, flower EO exhibited the strongest hydroxyl radical scavenging and reducing power, while peel EO had the highest total phenolic content. Differential metabolite analysis highlighted extensive divergence, with 834 metabolites differing between peel and flower EOs (815 upregulated in peel). Notably, 2-Methoxy-3,5-dimethylpyrazine, a potent odorant with a 0.4 ppb threshold was significantly enriched in peel EO, along with high-impact volatiles like α-citral, 2,4-decadienal, and 2-octanol acetate. Conclusion Red mandarin tissues possess distinct metabolite architectures. The peel is a rich reservoir of phenolics and high-impact odorants, making it a prime candidate for the food and fragrance industries. The flower and leaf EOs harbor unique aromatic and bioactive traits suitable for specialized nutraceutical or cosmetic applications. These findings strongly support the differentiated, value-added utilization of all three by-products.