The polyphenol study by HPLC-DAD-MS/MS ESI allowed the identification of two compounds previously not reported in lettuce;
quercetin and luteolin rhamnosyl-hexosides. Qualitative and quantitative differences were observed between the polyphenol profiles.
Caffeic acid derivatives were the main phenolics in green varieties, while flavonols were detected in higher quantities in red varieties
and escarole, and anthocyanins were only present in red-leafed varieties. The highest total phenolic content was observed in red-leafed
varieties while the highest level of vitamin C was detected in the continental variety. The red varieties showed the highest antioxidant
activity by all the methods assayed.