Absence of a clear relationship between lipid pathway enzymes and volatile compounds in fresh tomatoes

Specific activities of lipoxygenase (LOX), hydroperoxide lyase (HPL), and alcohol dehydrogenase (ADH) were determined at green, pink, and red stages of ripeness in twelve tomato selections ripened during storage. The interrelationships among lipid-derived volatiles and the activities of these three enzymes in these twelve selections were evaluated. LOX and HPL showed highest activities at the pink stage of ripeness, whereas ADH was most active at the red stage. Variability of enzyme activity among individual fruit and of hue angle within ripeness stage was great. There were differences among the twelve lines for each of the enzyme activities, suggesting the potential for altering tomato flavor by selecting lines with different enzyme patterns. A wide difference in mean enzyme activities and concentrations of measured volatiles was noted. Predictive models were developed for hexanal, trans-2-heptanal, pentenone, cis-3-hexenal, trans-2-hexenal, cis-3-hexenol, and methanol as a function of one or more of the enzymes studied. Enzyme activity itself was not found to be a good predictor of the amount of volatiles produced suggesting that genetic modification of a single specific enzyme is not likely to produce a beneficial effect on fresh tomato flavor.