The observation that F-acids (1) occur in rat chow initiated a search for F-acids in human diet. We observed that the amount of F-acids with a pentyl side chain in alpha-position taken up with a one-day diet correlates well with the amount of excreted degradation products, the pentyl urofuran acids (2), (3) and (4). Therefore it can be concluded that F-acids with a pentyl side chain are not produced in the human body but are introduced through the diet. The origin of F-acids carrying an alpha-propyl side chain is less clear. The amount of propyl-urofuran acids (2) and (3) excreted in urine was found in one case out of three to be five times higher than the amount of F-acids carrying a propyl group in alpha-position taken up by the diet. Therefore, it can presently not be excluded that a portion of the propyl F-acids is produced by the body. F-acids found in human food are mainly introduced into the body by vegetables and fruits. F-acids were found also in birch leaves in considerable amounts, as well as in grasses, dandelion and clover leaves. Thus, we can conclude that F-acids are common constituents of plants.

The nonvolatile fractions of cold-pressed peel oils of Key and Persian lime as well as grapefruit were separated by high-speed countercurrent chromatography (HS-CCC). In addition to the isolation of the main coumarins, psoralens and polymethoxyflavones, a number of minor constituents were enriched and successfully characterized by GC-MS and HPLC-UV. 5,7,8-Trimethoxycoumarin and the cyclical acetals of oxypeucedanin hydrate with citral were determined as new nonvolatile trace constituents of lime oils and confirmed by NMR spectroscopy. The citral oxypeucedaninyl acetals were found particularly in Key lime oil type A, which as a result of the juice-oil contact, is exposed to acidic conditions during industrial processing. Some of the confirmed minor constituents, such as pabulenol, isooxypeucedanin, and oxypeucedanin methanolate in lime as well as auraptenol in grapefruit, may have been generated by hydrolysis-sensitive precursors during CCC separation or their respective industrial processing techniques.

The coumarin fraction of cold-pressed Sicilian lemon oils (Citrus limon (L.) Burm. f.) was investigated by HPLC, MS, GC-MS and NMR. Twenty-nine structurally different compounds were identified. Eleven of these were previously unknown as constituents of lemon oil. S-(2,3'-Dihydroxy-3'-methylbutyloxy)-7-methoxycoumarin, 5-(2',3'-epoxy-3'-methylbutyloxy)-7-methoxycoumarin, 8-(7',8'epoxygeranyloxy)psoralen as well as 5-(3'-methylbut-2'-enyloxy)-8-(2",3"-dihydroxy-3"-methylbutyloxy)psoralen are hitherto unknown natural products. Moreover, a new derivatization method for the investigation of allyloxycoumarins, based on mild hydrogenation, is presented.

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The germacrene composition of various citrus peel oils was investigated. Detection and quantification of the thermally sensitive germacrenes A and C was achieved by employing extremely gentle GC conditions with 100°C maximum in injector and GC-oven. Germacrene A was found in all analyzed citrus oils with values from trace level to 0.46% of the volatiles, depending on variety and provenance. Germacrene C was identified in the peel oils of bergamot, bitter orange, lime, Minneola, Ortanique tangor, pummelo, Sweetie, tangerine and Yuzu with values of O.Ol-O.ijY%. In this context, germacrene C always occurred accompanied by germacrene B. Germacrene D was present in all citrus peel oils, with the exception of lemon, whereas bicyclogermacrene was a constituent of all examined citrus oils, except for lime. Distilled lime oil as acidic steam distillate possesses a special position, as it contained only germacrene B.