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Interactions between volatile compounds and BLG in aqueous solution were studied using static and dynamic headspace techniques (exponential dilution). The intensity of interactions between methyl ketones (C7-C9), ethyl esters (C6-C9), limonene, myrcene, and beta-lactoglobulin (BLG) were estimated by determination of the relative infinite dilution activity coefficients (gamma(r)). For a constant pH value, the methyl ketones retention by BLG increased significantly with the hydrophobicity of the volatiles, whereas the retention reached a maximum for ethyl octanoate in the ester series, indicating a possible steric hindrance. For limonene and myrcene an unexpected increase in headspace concentration or "salting out" effect was noticed for acid pH. The variations of the retention according to the pH increase of the medium from pH 3 to pH 11 could be related to structural modifications of the BLG. The retention increase observed between pH 3 and pH 9 resulted from the flexibility modification of the protein, allowing better accessibility to the primary or the secondary hydrophobic sites, whereas the dramatic decrease observed at pH 11 was the consequence of the alkaline denaturation of BLG. Electrostatic interactions occurring at pH 7.5 could also explain the observed retention increase.

Five mandelonitrile glycosides have been detected in the glycosidic fraction isolated from several Passiflora fruits using GC/EI-MS or GC/NCI-MS of trifluoroacetylated derivatives. Reasons for the possible co-occurence of prunasin and sambunigrin in passion fruit juice and peel are given, and amygdalin is reported for the first time as a passion fruit component. Two mandelonitrile rhamnopyranosyl β-d-glucopyranosides have been tentatively identified by MS. The extraction of cyanoglycosides using Amberlite XAD-2 followed by GC analysis of TFA derivatives was found to be an efficient method for their rapid determination. Prunasin was found to be the most important cyanogenic glycoside in peel (285 mg/kg for P. edulis f. flavicarpa), whereas amygdalin (31 mg/kg for P. edulis) and the two compounds tentatively identified as mandelonitrile rhamnopyranosyl β-d-glucopyranosides were mostly found in the juice (99 mg/kg for P. edulis f. flavicarpa). Different amounts of sambunigrin were found in the juice and the peel (from 0.4 mg/kg in P. edulis juice to 15.5 mg/kg in P. edulis f. flavicarpa peel). Keywords: Passion fruit; cyanogenic glycosides; gas chromatography; mass spectrometry