Comparison of Polyphenols, Flavonoids and Antioxidant Activities of Different Varieties of Lettuce

Lettuce is rich in various phenolic acids and flavonoids, making it a good source of dietary polyphenols. This study measured the contents of total phenols and flavonoids and antioxidant capacity of 50 varieties of lettuce (34 green lettuce varieties and 16 red lettuce varieties). Meanwhile, 17 characteristic phenolic acids and flavonoid compounds in lettuce were identified and quantitated using ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-ToF-MS) and ultra-high performance liquid chromatography (UPLC). Then, multivariate statistical analysis was used for classification and correlation analysis. The results showed that the contents of total phenols, total flavonoids, and antioxidant capacity of red lettuce varieties were higher than those of green lettuce varieties. In total, 7 phenolic compounds, namely, chlorogenic acid, caffeic acid, isochlorogenic acid A/B, chicory acid, and luteolin-7-O-β-D-glucuronide, quercetin-3-O-glucuronide, and quercetin-3-O-glucoside were detected, being overall more abundant in red lettuce varieties than the other varieties. The results of multivariate statistical analysis indicated that chlorogenic acid, luteolin-7-O-β-D-glucuronide, and quercetin-3-O-glucoside had higher correlation with the antioxidant capacity of lettuce. In summary, five new red varieties and commercial varieties, such as G21K104, W3088, and H20K6160, and four new green varieties, including G21K212 and G21K117, had higher antioxidant activity. This study provides a reference for lettuce breeding, germplasm resource innovation, and the development of nutritious, healthy and functional products.