Vegetable tissues can be dried and encapsulated for use as lutein and β-carotene dietary supplements (Müller et al., 1999). Therefore, lutein and β-carotene expressed on a DM basis were calculated (Table 3). Leaf age had an influence on lutein DM (P ≤ 0.001) and β-carotene DM (P ≤ 0.001). Both lutein DM [lutein DM = 0.4 + 0.5(AGE) − 0.08(AGE)2; r2 = 0.27, P ≤ 0.001] and β-carotene DM [β-carotene DM = 0.2 + 0.4(AGE) − 0.05(AGE)2; r2 = 0.56, P ≤ 0.001] responded quadratically to increases in kale leaf age.