Stem Lettuce and Its Metabolites: Does the Variety Make Any Difference?

The objective of the present study was to characterize chemical composition of hitherto unexamined aerial parts of Lactuca sativa var. angustana cv. Grüner Stern. In contrast to leafy and head varieties of the lettuces, asparagus lettuce grown in Europe is much less studied. Fractionation of a methanolic extract from leaves of L. sativa cv. Grüner Stern, supported with HPLC/DAD and (1)H NMR analysis, led to the isolation and/or identification of numerous terpenoid and phenolic compounds, including five apocarotenoids—(-)-loliolide, (+)-dehydrovomifoliol, blumenol A, (6S,9S)-vomifoliol, and corchoionoside C; three sesquiterpene lactones; two lignans—((+)-syringaresinol and its 4-O-β-glucoside); five caffeic acid derivatives; and three flavonoids. Some of the compounds, to the best of our knowledge, have never been isolated from L. sativa before. Moreover, monolignols, phenolic acids and a tryptophan-derived alkaloid were found in the analyzed plant material. Stems, leaves and shoot tips of the asparagus lettuce were examined to assess their phenolics and sesquiterpene lactone content as well as DPPH scavenging activity. Another stem lettuce—L. sativa var. angustana cv. Karola, two cultivars of leafy lettuces and one species of wild lettuce—L. serriola, were also examined as a reference material using HPLC/DAD. The results have been discussed regarding our previous studies and the literature data available.