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Incubation of linoleic acid with crude homogenate of tomato fruit gave a high yield (69%) of linoleic acid hydroperoxides with a ratio of 9- to 13-hydroperoxide isomers of 96:4. After chromatography of the products, as free acids or methyl esters, hydroperoxides with 9- to 13-isomeric ratios of greater than 99:1 were obtained. The major product was characterized as 9-D-hydroperoxy-octadeca-trans-10,cis-12-dienoic acid. The results demonstrate the positional specificity of lipoxygenase from tomato fruit.

Physical disruption of tomato fruits results in the degradation of endogenous lipids by hydrolytic and oxidative enzymes. Acyl hydrolase, phospholipase D, lipoxygenase and hydroperoxide cleavage enzymes are active in this tissue. A sequential enzymic pathway is proposed by which tissue lipids are hydrolysed to free (mainly polyunsaturated CIS) fatty acids which are subsequently oxidised to their hydroperoxides by lipoxygenase action. The CIS hydroperoxides are cleaved (by an enzyme which is specific for 13-hydroperoxide isomers) to volatile CS aldehydes (hexanal or cis-3-hexenal) and non-volatile CIZ o-oxoacids. The non-volatile fragment from linoleic acid was identified as 12-0x0-dodec-cis 9-enoic acid.