Changes in the steryl lipid content and composition of tomato fruit during ripening

Abstract

The content and sterol composition of free sterols (FS), steryl esters (SE), acylated steryl glycosides (ASG) and steryl glycosides (SG) were determined in outer pericarp tissue from ‘Rutgers’ tomato fruit, ranging from mature green to red ripe, and from fruit of three isogenic non-ripening mutants, rin, nor and Gr. The stigmasterol:sitosterol ratio in the four steryl lipids showed a large increase with ripening of Rutgers fruit, but only a small rise in rin, nor and Gr fruit of comparable age. Sitosterol and stigmasterol were the two major sterols in FS, SG and ASG, composing > 80% of the total in both ‘normal’ and mutant tomatoes. In SE, the proportion of stigmasterol was much lower and that of cholesterol and/or methyl sterols substantially higher. The content of FS, SG and particularly SE increased during ripening of Rutgers fruit, while there was little change in the content of ASG. Increases in the content of FS, SG and SE were far less in pericarp of rin mutant fruit. Thus, the changes noted in the steryl lipid content and composition of normal tomato fruit appear to be associated with ripening rather than with aging.