The sensitivity of a stable isotope dilution assay for 4-methoxy-2-methyl-2
-butanethiol (MMB) causing the blackcurrant-like odour in olive oils was im
proved. After spiking the oil sample with labelled MMB, the thiols were sep
arated from the volatile fraction with an immobilized reagent for thiols. M
MB and its standard were purified by multi-dimensional gas chromatography o
f the thiol fraction and determined by mass spectrometry. The new procedure
was applied to three Spanish oils differing in the intensity of their blac
kcurrant-like odour note. The concentrations of MMB lay between 0.4 mu gkg(
-1) and 4.3 mu gkg(-1). (C) 1998 Elsevier Science Ltd. All rights reserved.