Antioxidant capacity of capacity of leafy vegetables as affected by high tunnel environment, fertilisation and growth stage

BACKGROUND: This study was conducted to evaluate the influences of protected environment, organic fertilisation and growth stage on the oxygen radical absorbance capacity (ORAC) values of leafy vegetables. RESULTS: In a first experiment, pac choi grown in high tunnels had significantly lower ORAC than field-grown plants. Organic fertiliser markedly increased the antioxidant capacity of pac choi compared with conventional treatment, especially in the open field. However, both open field and organic production resulted in significantly lower yield and more severe leaf damage due to insect attack. In a second study, spinach showed the highest ORAC, followed by pac choi, red leaf lettuce and romaine lettuce. A significant decline in ORAC under high tunnel production was observed only in spinach. In contrast to the first trial, organic fertilisation did not cause an increase in antioxidant capacity of the leafy vegetables. The ORAC values of spinach from the open field and pac choi from high tunnels were significantly higher when harvested at the mature head stage than at the baby size stage. CONCLUSION: Further studies will help to elucidate effects of genotype, growth stage, and production environment on antioxidant capacities of vegetables and may lead to recommended practices to maximise antioxidant capacity of vegetable crops. (c) 2007 Society of Chemical Industry.