Distribution of flavour components in onion (Allium cepa L.), leek (Allium porrum) and garlic (Allium sativum)



Dry bulb onions and leeks, at the marketable stage of development, were dissected into nine and ten fractions respectively, comprising the stem and leaves in succession from the oldest outer layers. Each fraction was separately analysed for flavour components by determination of thiosulphinate and pyruvate. Similarly, garlic cloves were divided into five fractions. There was a consistent pattern of flavour distribution in the seven onion varieties studied. The dried outer scales were virtually free from flavour components, the concentrations of which (on a fresh weight basis) increased progressively from a minimum value in the outer leaf to the innermost tissue and the stem. The latter often contained more than twice the concentration present in the outer leaf. The pattern in the roots and edible portions of leek differed in detail from that in onion. Flavour intensity increased progressively from the outer leaf to the inner tissues and the concentrations in both the roots and the stem were approximately equivalent to that of the fourth leaf numbered from the outer leaf. The pattern of flavour distribution in garlic cloves was simpler than that of onion and leek. The storage leaf accounted for the bulk of the weight of the clove as well as its flavour content. Some aspects of knowledge of the metabolism of inorganic nitrogen and sulphur compounds in roots and other tissues and transport of the corresponding metabolites have been briefly reviewed as the basis of a preliminary interpretation of the above observations. Attention has been drawn to the bearing of the results on preparation of onion for cooking and processing and on sampling for analysis.