Color of Lettuce Determines Its Antioxidant Effect



Lettuce, one of the indispensable vegetables in the Mediterranean diet, is a food that greatly benefits health, mainly because it is rich in antioxidants. But not all lettuce varieties have the same antioxidant effect. According to a new study, the color of the leaves determines the speed at which their compounds act, so lettuces with green leaves have antioxidants that react more slowly, while red-leaf ones have a faster effect. The results of this study have been set out in a paper “Phenolic Composition and Related Antioxidant Properties in Differently Colored Lettuces: A Study by Electron Paramagnetic Resonance (EPR) Kinetics” recently published by the Journal of Agricultural and Food Chemistry.

Antioxidants provide long-term protection against the chain reactions of free radical processes that cause cellular damage and promote a wide variety of diseases. Free radicals harm our body by causing, in the best of cases, aging and, in the worse, serious diseases. Lettuce is rich in antioxidants, as it contains nutrients like phenolic acids, flavonoids, anthocyanins, and vitamins A and C, among other compounds.

Green, semi-red and red leaves

To conduct their study the researchers analyzed the compounds of three lettuce varieties: the green-leaf ‘Batavia’, the semi-red-leaf ‘Marvel of Four Seasons’, and the red-leaf ‘Oak Leaf’. Using Electron Paramagnetic Resonance (EPR) techniques, the researchers were able to observe the behavior of the kinetics of the compounds of each variety. The results show that green-leaf lettuce contains water-soluble, antioxidant compounds that act at a slow and intermediate speed, red-leaf lettuce has compounds with intermediate and rapid kinetics, and semi-red-leaf lettuce has three kinds of compounds, with a rapid, intermediate and slow speed.

As lead researcher, Dr. Pérez-López stressed, “the fact that there are compounds that act at different speeds does not mean that some are better or worse than others. If we eat foods that can generate free-radical activity, there will be some compounds that act to eliminate them more quickly. But at the same time, it is also important that our bodies should acquire foods with antioxidants that have slower kinetics so that the latter will continue to act over a longer period of time. That is why people say that it is very interesting to mix different types of lettuce because they have different, complementary characteristics.”

Boosting Antioxidant Properties

Having determined the kinetics of the antioxidants, the research is currently continuing with the aim of achieving a nutraceutical improvement of these three varieties of lettuce. The research group is now trying to boost the effect of the specific compounds in each variety by subjecting the plants to short stresses.

These compounds perform defense functions in plants. So if conditions that are not the normal ones are applied to them (such as watering them with salinated water, subjecting them to high lighting intensity or working with raised concentrations of CO2), these defenses will become intensified and, as a result, the antioxidant qualities of the plants will be boosted.

“What matters in this process is not to lose productivity, and that is why we apply short-intensity stresses. With excessive stress, we could reach a point in which plant growth is reduced, and we are not interested in achieving greater quality at the cost of a reduction in size. The aim is to maintain production and achieve greater quality in this production,” pointed out Pérez-López.

Source: Usue Pérez-López, Calogero Pinzino, Mike Frank Quartacci, Annamaria Ranieri, Cristina Sgherri. Phenolic Composition and Related Antioxidant Properties in Differently Colored Lettuces: A Study by Electron Paramagnetic Resonance (EPR) Kinetics. Journal of Agricultural and Food Chemistry, 2014; 62 (49): 12001 DOI: 10.1021/jf503260v.

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