AUTHENTICATION OF GREEN COFFEE VARIETIES ACCORDING TO THEIR STEROLIC PROFILE

Sterols of 31 samples of green coffee beans of the arabica and robusta varieties have been analysed by gas chromatography flame ionization d etector. The lipids were Soxhlet extracted from ground coffee beans in to hexane. The extract was evaporated and the residue was treated with 0.2% of Sa-cholestane-SP-ol (internal standard). The lipids were sapo nified and the sterolic fraction of the unsaponifiable part was separa ted by thin layer chromatography. Sterols were treated with a silylati ng reagent to convert them into trimethyl silyl derivatives. This anal ysis was performed on a column (30 mx0.32 mm i.d.) coated with a bonde d stationary phase HP-5 (5% diphenyl-95% methylpolysiloxane; 0.2 mu m) with hydrogen (0.7 ml min(-1)) as a carrier gas, isothermal temperatu re at 265 degrees C and flame ionization detector. By using the sterol s as chemical descriptors pattern recognition techniques were applied to differentiate between arabica and robusta green coffee varieties. D elta(5)avenasterol and sitostanol were found to be the most differenti ating variables. (C) 1998 Elsevier Science B.V. All rights reserved.