6-(BUT-2'-ENYLIDENE)-1,5,5-TRIMETHYL-CYCLOHEX-1-ENES - IMPORTANT VOLATILE CONSTITUENTS OF THE JUICE OF THE PURPLE PASSIONFRUIT PASSIFLORA-EDULIS

Two important flavour components of the juice of the purple passionfruit Passiflora edulis (Sims) have been shown by g.l.c., mirco-reaction g.l.c., u.v., i.r., n.m.r., mass spectrometry, and by synthesis to be (6E, 2′E)- and (6Z, 2′E)-6-(but-2′-enylidene)-1, 5, 5-trimethylcyclohex-1-ene (2a) and (2b). Evidence is also reported for the presence in this juice of trace amounts of the stereoisomers (2c, d). The 6-(but-2′-enylidene)-1, 5, 5-trimethylcyclohex-l-enes are very susceptible to oxidation and, in dilute acetic acid solution, are rapidly converted into 'ionene', 1, 1, 6-trimethyl-1, 2, 3, 4-tetrahydro-naphthalene (10). The significance of this reaction in the loss of flavour during pasteurization of passionfruit juice is discussed. © 1979, CSIRO. All rights reserved.