Abstract
Watercress (Rorippa nasturtium-aquaticum), wild rocket (Diplotaxis tenuifolia), and spinach (Spinacia oleracea) are commercial crops reported to have high concentrations of antioxidants, possibly contributing to disease prevention following human consumption. Following analysis of supermarket-purchased salad leaves, we report the antioxidant content potential of these species using two comparable techniques assessing the consistency between the assays – by the ferric reducing antioxidant power (FRAP) assay and the oxygen radical absorbance capacity (ORAC) assay. The leaves were harvested from both conventionally and organically managed crops, to investigate whether organic agriculture results in improved crop quality. Watercress had the highest FRAP and ability to scavenge free radicals, followed by spinach and rocket. For watercress and rocket, there was no significant effect of organic agriculture on FRAP and ORAC, but for spinach, the antioxidant potential was reduced and this was significant at the 5% level of probability for FRAP but not ORAC, although the trend was clear in both tests. We conclude that there is variation in salad crop antioxidant potential and that FRAP and ORAC are useful techniques for measuring antioxidants in these salad crops with similar ranking for each salad crop studied.
Highlights
In recent years, interest in the antioxidant status of plantderived foods has risen due to the potential health benefits from their ability to scavenge radicals (Podsedek 2007)
The ferric reducing antioxidant power (FRAP) assay is the only assay that directly measures antioxidants in a sample compared to other assays measuring inhibition of free radicals (Halvorsen et al 2002)
It is important to note that the organic spinach had a significantly lower antioxidant activity than conventional spinach while there was no significant difference between organic and conventionally grown watercress and rocket
Summary
Interest in the antioxidant status of plantderived foods has risen due to the potential health benefits from their ability to scavenge radicals (Podsedek 2007). A free radical is a free atom, molecule, or ion which contains one or more unpaired electrons (Aruoma et al 1993). The term “antioxidant” covers a wide range of different molecules but a common feature is their ability to readily donate electrons while remaining stable themselves, acting as reducing agents (Aruoma 1998) and minimizing damage caused by free radicals. Antioxidants present in plants (acting as a defense system within the plant) can deactivate radicals by two major mechanisms: hydrogen atom transfer (HAT) and single electron transfer (SET), both produce a similar end result (Prior et al 2005).
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