Search

EARLIER1, we reported the presence in the natural coating of ‘Granny Smith’ apples of a hydrocarbon which we identified as the naturally occurring sesquiterpene β-farnesene (I)2–4. Identification was based on a comparison of its infra-red spectrum with that published for β-farnesene isolated from natural sources4, together with the unequivocal identification of its fully hydrogenated product as farnesane (2,6,10-trimethyldodecane)2,3by comparison of its infra-red and mass spectra and gas chromatographic retention times with those of a pure authentic specimen. Additional evidence was, however, deemed necessary, and direct comparison with pure β-farnesene has now established that this identification was incorrect and that the farnesene present in apple coating is not the β- but the α-isomer (II), which has hitherto not been reported as naturally occurring or prepared in a pure state.

PREVIOUS investigation of the cuticle oil of the ‘Granny Smith’ apple in this Laboratory indicated the presence of small amounts of a hydrocarbon with a conjugated diene absorption in the ultra-violet. In view of its possible connexion with the serious storage disorder ‘superficial scald’ it was isolated, and it has now been identified as the sesquiterpene farnesene (2,6-dimethyl-10-methylene-2,6, 11-dodecatriene)1,2.

SINCE Gane1identified ethylene as a volatile product of ripening apples, other workers2–4have demonstrated its production by other fruits, leaves and the fungus Penicillium digitatum. The identification by conversion to ethylene dibromide and then to the crystalline substance NN′-diphenylethylene-diamine established ethylene as the predominant olefine, but did not specifically exclude higher homologues the derivatives of which could be lost during crystallization of the main product. As the volatile emanations of apples include a series of acids and alcohols with one to six carbon atoms5–7, the absence of a corresponding series in the olefines cannot be accepted without rigorous proof.

BARRON et al.1showed that ascorbic acid is not autoxidizable in acid solutions up to pH 7. They investigated the catalytic effect of salts of manganese, nickel, iron, cobalt, calcium and copper at pH 4–6 and found that copper alone had a marked catalytic effect. Mack and Kertesz2found that iron had no catalytic effect alone but increased the catalytic effect of copper.