Characterisation and variation of antioxidant micronutrients in lettuce (Lactuca sativa folium)

The main phenolic compound in six studied lettuce cultivars (five green and one red) was identified as dicaffeoyl tartaric acid. Quantitative but not qualitative differences were found in the phenolic profiles among green cultivars. The red oak leaf cultivar contained twofold more dicaffeoyl tartaric acid and 10-fold more chlorogenic acid than the green cultivars. Total phenolics ranged from 8.4 to 12.9 mg g^-1 dry weight in green varieties and reached 27.8 mg g^-1 dry weight in red oak leaf. Carotenoids and vitamins E and C were also quantified. Lutein was the main carotenoid found in all cultivars, together with another xanthophyll. The period of harvesting had only a marginal influence on total phenolic levels, whereas carotenoid and vitamin E levels were higher at the second period of harvesting. Vitamin C levels ranged between 6.1 and 9.9 mg per 100 g fresh weight. We investigated the total antioxidant power in lettuce. Total phenolics accounted for more than 60% of the total antioxidant capacity. Dicaffeoyl tartaric acid accounted for 55%.