The compositions of Vietnamese pummelo (Citrus grandis Osbeck), orange (C. sinensis Osbeck), tangerine (C. reticulata Blanco var. tangerine) and lime (C. limonia Osbeck) peel oil samples have been investigated by GC and GC-MS. The essential oils were extracted by the cold-pressing method. Hydrocarbons, followed by aldehydes and alcohols, were the most abundant compounds in all four kinds of samples. Their percentages, respectively, were >98.7%, >97.6%, >98.6% and >95.4% in hydrocarbons; >0.3%, 0.4%, >0.3% and 1.1% in total aldehydes; 0.2%, 0.5%, 0.4% and 0.7% in alcohols. In Vietnamese pummelo oil, -terpinene was not detected, while terpinolene was detected in small amounts and nootkatone only at a level of <0.05%. Orange oil composition was comparable to that of other sweet orange oils. υ-3-Carene was detected at a level of 0.1%. Tangerine oil is easily distinguished from other citrus oils by its content of various aliphatic aldehydes. Lime oil presented a very different composition from the other oils studied. Its limonene content was substantially lower than that of pummelo, orange and tangerine oils, whereas -terpinene,ˇ-pinene and˛-pinene occurred in higher proportions, moreover, the sesquiterpene hydrocarbon fraction of this oil is qualitatively more complex and quantitatively more abundant than in the other oils.

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In the isotope ratio (Ir) analysis using GC-MS, several variable factors in sampling incidental to any food analysis were investigated for yuzu fruit. The Irs of ten monoterpene hydrocarbons in yuzu essential oils from each of six fruiting positions of three trees were measured. The sign test following t-test of all the Ir values demonstrated that there was no significant difference between both sampling years of 2001 and 2002. There was also no significant variation in the Ir values among the three trees and six fruiting positions in the individual two years.Key words: isotope ratio analysis; sampling variations; HRGC/MS; monoterpene hydrocarbon A determination of the isotope values of constituents is gaining increasing importance, especially in view of the increased demand in the fragrance and food industries for the authenticity control and origin determination of the production of essential oils and foods.1-3) Recently, many sensational articles have been reported on dishonest designations of raw foods, since the JAS (Japanese Agricultural Standards) were revised on July 2000. The authors 4) have developed a specific and convenient method for characterization of yuzu (Citrus junos Tanaka) fruits produced in different districts by the isotope ratio of monoterpene hydrocarbons with HRGC-MS. This method will be applicable to several cases such as differentiation of the quality, evaluation of genuineness of vegetable products from various producing districts, and classification of the species. It is noticed that this analytical method will be useful for chemical evaluation of agricultural products, in addition to DNA analysis. 5,6) The authors 7,8) have also reported successful results on the discrimination of commercial citrus essential oils of different origins, and the accuracy of the Ir method using 13 C-labeled compounds. There remain, however, some questions about samplings from the fundamental scope. In order to normalize this method, the variations or individual differences which each material substantially owns should be further investigated. This paper concerns the effects of variable factors involved in fruit samples regarding the isotope ratio analysis.Three yuzu trees (13-to 15-years age) were selected at random among a number of yuzu trees under the usual cultivation in the field of Kochi Fruit Tree Experimental Station, Kochi. The experiments were done from the following three viewpoints: (1) 9) The yield of CPO was 0.10-0.16 g/100 g of fresh fruit, and 0.34-0.59 g/100 g of flavedo. Each CPO sample was kept at À25 C until needed for analysis. Gas chromatography-mass spectrometry (GC-MS) was done with a Shimadzu GC-17A linked to a Shimadzu QP-5000. The GC column was a DB-Wax fused silica capillary (60 m  0.25 mm i.d., 0.25 m film thickness; J & W Scientific, Folsom, CA, U.S.A.) The analytical conditions of GC-MS and column temperature were the same as those of the previous paper.4) The isotope ratio (Ir) of the selected monoterpene hydrocarbons in CPO, m=z 137/136, was measured by selected-ion m...

The isotope ratio of monoterpene hydrocarbons in citrus essential oils of different origins was measured by ordinary high-resolution gas chromatography-mass spectrometry (HRGC-MS). The isotope ratio (Ir) was determined by the ratio of the isotope peak intensity (m/z 137) to the molecular mass peak intensity (m/z 136) of the monoterpene hydrocarbons. The accuracy of Ir was examined by measuring monoterpene hydrocarbon standards and 13C-labeled compounds. The isotope fingerprints based on the values of monoterpene hydrocarbons from lemon, lime and yuzu essential oils were determined. These citrus essential oils were also discriminated by a principal component analysis of their Ir data. The characteristic vectors showed that alpha-terpinene, beta-pinene and beta-phellandrene were important components for distinguishing between the citrus species. It is suggested that this technique will be applicable to evaluate the quality, genuineness and origin of citrus fruits and their products.