Quantitative analysis of flavour precursors and pyruvate levels in different tissues and cultivars of onion (Allium cepa)

Onions of three different cultivars were dissected as in commercial peeling operations to give four tissue types: the dry, brown skin, the top/bottom sections, the outer fleshy leaf bases and the inner fleshy leaf bases. All tissue types were assayed for alliinase-produced pyruvate and for flavour precursors (alk(en)yl cysteine sulphoxides) and a positive correlation was observed between the levels of these classes of compounds. In all cultivars, the top and bottom onion sections have the highest levels of both pyruvate and flavour precursors with levels in the dry, brown skin being low or absent. Significant increases in levels of both pyruvate and flavour precursors were observed in inner tissues and top/bottom sections after storage under commercial conditions.