Identification and quantification of selected metabolites in differently pigmented leaves of lettuce ( Lactuca sativa L.) cultivars harvested at mature and bolting stages

摘要

Background: Identifcation and screening of cultivars rich in bioactive phytoconstituents can be potentially useful tomake nutrient?dense dishes and in medicinal formulations. In this study, we have identifed, characterized and quanti?fed cafeoylquinic acids, dicafeoylquinic acid, dicafeoyltartaric acid, kaempferol conjugates, quercetin malonylglu?coside, sesquiterpene lactones, and cyanidin in 22 lettuce cultivars at mature and bolting stages using UPLC?PDA?Q?TOF?HDMS, UPLC, and HPLC.Results: The composition and contents of the studied metabolites and antioxidant activity varied signifcantly anddepend on leaf color, cultivar type and stage of maturity. The main phenolic acid components of lettuce were quinicand tartaric acid derivatives, whereas kaempferol derivatives were the dominant favonoids. The sum of the contentof phenolic acids ranged from 18.3 to 54.6 mg/100 g DW and 15.5 to 54.6 mg/100 g DW, whereas the sum of thecontents of favonoids ranged from 9.2 to 25.9 mg/100 g DW and 14.9 to 83.0 mg/100 g DW in mature and boltingstage cultivars, respectively. The content of cyanidin, lactucin, lactucopicrin, and ABTS radical antioxidant activity werein the range of 0.3 to 9.7 (mature stage) and 0.5 to 10.2 mg/g DW (bolting stage), 1.8 to 41.9 (mature stage) and 9.7to 213.0 (bolting stage) μg/g DW, 9.9 to 344.8 (mature stage) and 169.2 to 3888.2 (bolting stage) μg/g DW, and 12.1to 29.0 (mature stage) and 15.7 to 30.3 (bolting stage) mg TE/g DW, respectively. The principal component analysis(PCA) showed that the green and red pigmented lettuce cultivars were grouped to the negative and positive sidesof PC1, respectively, while the green/red pigmented cultivars were distributed throughout the four quadrants of thePCA plots with no prominent grouping. The loading plot showed that phenolic acids, favonoids, and cyanidin are themost potent contributors to the radical scavenging activity of lettuce extracts.Conclusions: Lettuce at the bolting stage accumulate relatively high amount of sesquiterpene lactones (SLs),quercetin malonylglucoside (QMG), methylkaempferol glucuronide (MKGR), kaempferol malonylglucoside (KMG), and3?O?cafeoylquinic acid (3?CQA) compared to the mature stage. Higher amount of phytoconstituents were found to beaccumulated in the red pigmented lettuce leaves compared to the green lettuce leaves. In addition, the contents ofmost of the metabolites in lettuce seem to increase with age of the leaves. The presence of the two bitter SLs, lactucinand lactucopicrin, in signifcantly high amount in lettuce leaves at bolting stage could diminish consumer acceptance.However, alternatively, these leaves could be utilized by nutraceutical companies working to recover these compounds.