Virtual freezing of the hemiacetal-ardehyde equilibrium of the aglycones of oleuropein and ligstroside present in olive oils from Carolea and Coratina cultivars by ionspray ionization tandem mass spectrometry

The composition of the equilibrium between aldehydes and hemiacetals was ev aluated by ionspray ionization tandem mass spectrometry. The methanolic ext racts of virgin olive oil from Carolea and Coratina cultivars contain a com plex mixture of hydroxytyrosol (3) and tyrosol (4) derivatives (5, 6) chara cterized by the presence of aldehyde moieties in equilibrium with their hyd rated form (8) or with the corresponding methanol hemiacetals 9 and 10, The equilibrium was frozen by droplet evaporation, thus allowing the structure determination of each component. The formation of the decarboxylated speci es 11-14, reported previously, was not observed. Copyright (C) 2000 John Wi ley & Sons, Ltd.