Other carotenoids such as a-carotene and lutein were not detectable in all analysed watermelon cultivars at any stage of ripening. This indicates the absence or a low expression of the lycopene a- and b-cyclase enzymes involved in cyclization of lycopene to a-carotene, which is converted into lutein by the action of b-ring hydroxylase. However, a small amount of lutein (1–3 mg/kg fw) has been reported in watermelon by other authors