INTRODUCTION The reputed health-giving properties of fresh garlic and commercial garlic extracts are thought to be derived from the presence and subsequent breakdown of the alk(en)yl- cysteine sulphoxides (CSOs), alliin, isoalliin and methiin (Block 1992; Lawson 1996; Collin 2004) which act as fla- vour precursors in a range of Allium species. These odour- less sulphur-containing cysteine derivatives are the final stable products of biosynthetic pathways and are stored in vesicles within the cytoplasm (Lawson 1996). However, when garlic tissue is damaged during culinary or manufac- turing activities, the enzyme alliinase is released from the cell vacuoles and can cleave CSOs simultaneously liberated in the cytoplasm. The reaction products are pyruvate, am- monia and a volatile, low molecular weight thiosulphinate which rapidly undergoes a series of vapour-phase non- enzymic reactions to yield a complex mixture of sulphur products that change over time (Block 1992). In garlic, un- like most other Alliums, the major flavour precursor is alliin that yields a series of thiosulphinates, allyl sulphides, dithi- ines and ajoenes after the action of alliinase and subsequent