PHYTOSTEROL BIOSYNTHESIS IN RIPENING TOMATOES

ABSTRACT Phytosterols from mature green tomatoes ripened under red light treatment or in the dark were extracted and quantitated by GLC at 3‐day intervals. Tomatoes ripened under light showed 8 phytosterols while those ripened in the dark showed 5 phytosterols. The 4 phytosterols identified and quantitated were cholesterol, campesterol, stigmasterol and β‐sitosterol. This is the first time cholesterol was identified in tomato pericarp tissues. Red light treatment advanced and slightly enhanced the biosynthesis of tomato phytosterols in comparison with tomatoes ripened in the dark. Approximately a 10% increase in total phytosterols was noted and the increase was attributed mostly to campesterol and stigmasterol. In mature green tomatoes, the phytosterol content was 37 mg/100g dry wt of which two‐thirds was β‐sitosterol. As the fruit matured, stigmasterol became the dominant phytosterol with β‐sitosterol closely behind. Peak phytosterol content was 106 mg/100g dry tissue at the ripe stage of maturation and the content declined as tomatoes became senescent. The results support the fact that the effect of red light on terpenoids biosynthesis was a general one and was not specific to carotenoids biosynthesis in ripening tomatoes.