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Allium odors were re-examined to determine whether or not they contain degradation compounds of thiosulfinates. Garlic (Allium sativum), leek (Allium porrum) and onion (Allium cepa) were investigated using cryotrapping and direct injection of aqueous solutions of the samples into a high-performance liquid chromatograph (HPLC), with a diode-array detector, coupled to a maw spectrometer (MS). Various commercial systems which couple HPLC to tandem MS, but using different ionization systems, were compared. Best results were obtained with atmospheric pressure chemical ionization although degradation of certain thiosulfinates was observed. Depending on the HPLC/MS interface, thiosulfinates formed dimers in variable quantity and this reaction could be used to differentiate isomeric 1-propenyl and 2-propenyl thiosulfinates. Some unresolved isomers were identified by their fragment ions. No disulfides or other rearrangement products were observed and it was concluded that Allium odors contain only thiopropanal S-oxide and thiosulfinates as sulfur volatiles.

The volatiles used by the parasitoid Diadromus pulchellus to find its host, the leek moth, are produced by the bacteria developing in the frass of the host larvae. The origin and the nature of these bacteria were investigated. Samples were taken from healthy leeks and from infested leeks in the field, as well as from the frass of larvae reared in the laboratory either on the host plant or on an artificial diet. The various species of bacteria identified were cultured in the presence of precursors of leek sulphur volatiles and their volatile emissions were analysed. Klebsiella oxytoca and various Bacillus, common decomposers of plant matter, were the principal species producing active volatiles which were alkyl disulphides.