Effect of leaf position on the distribution of phytochemicals and antioxidant capacity among green and red lettuce cultivars

In recent years, there has been an increasing interest in consumption of red fruits and vegetables due to its rich dietary sources of antioxidant, phenolics and anthocyanins. In this study, phytochemical and antioxidant properties of green and red lettuce cultivars were studied. Particularly, the effect of leaf position on these properties was compared. Eight conventionally grown cultivars of lettuce (Lactuca sativa L.), with four green (Fonseca, Freckles, Krizet and Filipus) and four red (Versai, Nation, Paradai and Cherokee) cultivars were studied. Their leaves were divided into three groups; outer, middle and inner part. Total antioxidant capacity (TAC) of each group of leaves was assessed by both trolox-equivalent antioxidant capacity (TEAC), and the ferric reducing antioxidant power (FRAP) assay. Leaf color, total soluble solids, total phenolics (TP), total anthocyanin (TACY), chlorophyll a and b were determined. The results demonstrated that outer leaves have the highest phytonutrient content and antioxidant properties. Outer leaves exhibited significantly higher TP and TAC than middle and inner leaves in both red and green color lettuce. The average TP content of red lettuce were 845, 297 and 195 µg gallic acid equivalent per gram fresh weight in the outer, middle and inner leaves, respectively. Also TAC of outer leaves was significantly higher than middle and inner leaves in both red and green color lettuce. The magnitude of difference between red and green cultivars was significant as determined by both TEAC and FRAP methods