Changes of the Volatile Profile and Artifact Formation in Daidai (Citrus aurantium) Cold-Pressed Peel Oil on Storage SIMON MUHOHO NJOROGE, † HIROYUKI UKEDA, ‡ AND MASAYOSHI SAWAMURA* ,‡ Department of Food Science and Technology, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000, Nairobi, Kenya, and Department of Bioresources Science, Faculty of Agriculture, Kochi University, B-200 Monobe, Nankoku, Kochi 783-8502, Japan The chemical changes and artifact formation in daidai (Citrus aurantium L. var. Cyathifera Y. Tanaka) cold-pressed peel oil upon storage at 20, 5, and -21 °C for 3, 6, and 12 months were investigated using capillary gas chromatography (GC) and GC-MS. Major changes occurred in the oil stored at 20 and 5 °C. No changes were found at -21 °C. Monoterpene hydrocarbons decreased from 98.0 to 66.4% upon 12 months at 20 °C, while sesquiterpene hydrocarbons and alcohols increased from 0.1 to 2.4% and from 0.3 to 7.9%, respectively. Notable decreases of germacrene D, myrcene, linalyl acetate, and limonene occurred. Prominent increases of cis-carveol, trans--farnesene, trans-p-2,8- menthadien-1-ol, linalool, and -caryophyllene were found. Thirty-four artifact compounds constituting 17.0% of the total volatile compounds were formed upon 12 months at 20 °C. The artifacts consisted of 13 alcohols (6.0%), five carbonyl compounds (5.3%), seven esters (4.9%), three epoxides (0.4%), four hydrocarbons (0.3%), and two unidentified. The prominent artifact compounds were (+)-carvone, trans,trans-farnesyl acetate, sabinene hydrate, 1-octen-3-ol, cis,cis-farnesyl acetate, and dihydro- carveol acetate. The results could be applied for monitoring and control of the flavor quality of daidai essential oil and related products. KEYWORDS: Daidai; Citrus aurantium L. var. Cyathifera Y. Tanaka; cold-pressed peel oil; storage temperature; storage time; volatile compound; compositional change; artifact compound; storage stability INTRODUCTION Stability of the volatile chemical constituents of essential oils during handling and storage is an important consideration for their various applications, such as food processing, cosmetics, perfumery, fragrances, and aromatherapy. Citrus oils are complex mixtures of volatile compounds, mainly the unsaturated monoterpene and sesquiterpene compounds, which are generally labile to heat and chemical reactions. The resultant composi- tional changes and artifact formation are important aspects of flavor chemistry in view of the possible off-flavor development and reduced quality and economic value of the product. Moreover, the presence of artifact compounds in laboratory samples of essential oils could limit the value of the analytical information obtained. Artifacts may be formed in stored oils upon oxidation, metal catalysis, or heat or chemical interactions of the naturally present compounds. Studies on Citrus essential oils have mostly dealt with characterization of the components present and given less attention to compositional changes influenced by handling and storage parameters. Investigations on storage stability of special cold-pressed oils (CPOs) are, therefore, very important. Citrus peel oils are much more steady than Citrus essence oils concerning storage stability. The better storage stability of the CPOs refers mainly to the nonvolatile residues (2-15%). These residues are coumarins, psoralens, and polymethoxylated flavones, which have antioxidative properties. These components and their quantity have to be considered by reflecting the stability of Citrus peel oils. Daidai (Citrus aurantium L. var. Cyathifera Tanaka) is a variety of the sour orange (C. aurantium L.) produced mainly in Japan and some parts of China. The actual quantities of daidai peel oil produced in China and Japan are not clearly known. The sour orange has been used for salad dressings, culinary, seasonings, and flavoring of beverages such as tea. Reported studies on volatile components of daidai oil have indicated a large proportion of monoterpene hydrocarbons (98.0%). Li- monene (p-mentha-1,8-diene) is the most dominant hydrocarbon, and linalyl acetate is the main oxygenated compound of the oil (1, 2). The ester in conjunction with -elemol has been indicated as the characteristic odor compound of daidai oil (2). Citrus oils are generally prone to oxidation, polymerization, and structural rearrangement during handling, analysis, processing, or storage, with associated changes of the volatile profile and aroma properties (3). If a major disturbance of the natural composition of the oil occurs, such that the relative concentration of the constituents is distorted, this would affect the subtlety of * To whom correspondence should be addressed. Tel: +81-88-864-5184. Fax: +81-88-864-5200. E-mail: sawamura@cc.kochi-u.ac.jp. † Jomo Kenyatta University of Agriculture and Technology. ‡ Kochi University. J. Agric. Food Chem. 2003, 51, 4029-4035 4029 10.1021/jf021215q CCC: $25.00 © 2003 American Chemical Society Published on Web 05/31/2003