On the genuineness of citrus essential oils .51. Oxygen heterocyclic compounds of bitter orange oil (Citrus aurantium L)

The composition of the oxygen heterocyclic fraction of bitter orange essential oil, obtained by normal-phase HPLC with two on-line coupled columns (mu-Porasil and Zorbax), is reported. Genuine, industrial, cold-pressed Italian and Spanish essential oils, commercial oils, laboratory hand-extracted oils, and mixtures of bitter orange oil with sweet orange, lemon, lime, and grapefruit oils were analyzed. Four coumarins (osthol, meranzin, isomeranzin, and meranzin hydrate), three psoralens (bergapten, epoxybergamottin, and epoxybergamottin hydrate), and four polymethoxyflavones (tangeretin, 3,3',4',5,6,7,8-heptamethoxyflavone, nobiletin, and tetra-O-methylscutellarein) were identified. In addition, three unknown coumarins were found. Meranzin was the main component isolated. Meranzin hydrate, the formation of which was probably due to the hydration of meranzin during the industrial extraction, was not found in the laboratory hand-extracted samples. Meranzin was not present in some industrial samples, probably because of a prolonged and unusual contact of the essential oil with an acid aqueous medium during the process of extraction. Italian essential oils usually exhibited a higher content of oxygen heterocyclic compounds than the Spanish oils. The bitter orange oils adulterated by sweet orange oil were characterized by a lower content of almost all the aforementioned components; the adulteration of bitter orange oils with lemon, lime, or grapefruit oils was detected by the presence of components peculiar to added oils.