Flavonoids and phenolic acids in lettuce: how can we maximize their concentration? And why should we?

C. Becker
Flavonoid glycosides and caffeic acid derivatives are widely distributed in the plant kingdom. Many crops owe their red or blue color to the presence of anthocyanins. Their hue depends on their structure, pH and presence of chelating metal ions. Obviously, they are important for visual plant quality. Furthermore, polyphenolic compounds like flavonoids and phenolic acids are reported to have beneficial effects on our health by providing high antioxidant and radical scavenging activity. Yet, studies on health promoting effects are discussed controversially. Results differ between in vitro and in vivo experiments which were conducted with single or several substances or plant extracts. Some of these differences are probably due to varying bioavailability, synergisms between substances and matrix effects. In plants, foliar flavonoids can serve as photoprotectants and shield the photosystem from excess energy and UV radiation. Additionally, they play important roles in the plants' interaction with other organisms, for example herbivores, and can increase the plants' resistance to fungal pathogens. Red leaf lettuce contains cyanidin, quercetin and luteolin glycosides as well as derivatives of caffeic acid. Lettuce does not contain exceptionally high concentrations of polyphenols. However, it is usually consumed raw and in large quantities. Several pre-harvest cultural measures are well suited to enhance their concentration. Among them are increasing radiation intensity (both UV and photosynthetically active radiation), low temperature, and low macro nutrient availability. For economical and health-related reasons it is very interesting to maximize the concentration of polyphenols in crops.
Becker, C. 2016. Flavonoids and phenolic acids in lettuce: how can we maximize their concentration? And why should we?. Acta Hort. (ISHS) 1142:1-10
Lactuca sativa, flavonoid glycosides, quercetin, luteolin cyanidin, phenolic acids, bioavailability, quality enhancement

Acta Horticulturae