Ripening‐induced acceleration of volatile aldehyde generation following tissue disruption in tomato fruit

Abstract

Hexanal and cis‐3‐hexenal are principal flavor volatiles in ripe tomato fruit, but whether they accumulate during ripening or are formed upon maceration of the tissue has not been clarified. This has been addressed by measuring levels of these aldehydes in green and ripe fruit with discrimination between intrinsic aldehyde content and aldehyde generation following tissue disruption. Volatile sampling of tomato fruit homogenates was accomplished by purge/trapping, followed by thermal desorption on a gas chromatograph equipped with a mass selective detector. Incubation of some samples with alcohol dehydrogenase to convert the aldehydes to their respective alcohols permitted positive identification of the isomeric form of hexenal as cis‐3‐hexenal. Red and green tomato fruit homogenized in buffer with saturated CaCl2 contained low (0.1‐0.8 µg g−1 fresh weight) levels of hexanal and cis‐3‐hexenal; thus there is minimal endogenous volatile content in intact fruit. Volatile levels increased rapidly, up to 10‐fold, following homogenization of ripe tomato fruit in the absence of CaCl2, and more modestly in corresponding green tomato fruit homogenates. Incubation with the appropriate lipoxygenase/hydroperoxide lyase substrate (linoleic acid for hexanal, linolenic acid for cis‐3‐hexenal) doubled the amount of volatile compound produced. Hexanal generation was suppressed in the presence of linolenic acid, suggesting that the enzyme complex has greater affinity for this substrate. As well, levels of cis‐3‐hexenal, but not hexanal, tended to decline within 30 min of homogenization, possibly reflecting a specific degradative process. The results collectively indicate that the contribution of six‐carbon aldehydes to tomato fruit flavor is attributable to metabolism invoked following tissue disruption rather than within the intact fruit.