Onion flavor chemistry and factors influencing flavor intensity

Although onions are an important vegetable and have nutritional value in diets around the world, they are primarily consumed for their distinctive flavor or their ability to enhance flavors in other foods. Onion flavor is dominated by organosulfur compounds arising from the enzymatic decomposition of S-alk(en)yl-L-cysteine S-oxide flavor precursors following tissue disruption. Compounds arising from precursor decomposition, such as the lachrymatory factor and various thiosulfinates give onions their characteristic flavors. Sulfate is absorbed by the plant and incorporated through cysteine to glutathione. From glutathione, sulfur can proceed through several peptide pathways and terminate in the synthesis of one of three flavor precursors. Flavor intensity is governed by genetic factors within the onion and environmental conditions under which the onions grow. Onion cultivars differ in the ability to absorb sulfate and in the efficiency of synthesizing flavor precursors. Increased sulfate fertility, higher growing temperatures and dry growing conditions all contribute to increased flavor intensity in onion.