Sesquiterpene Lactones and Bitterness in Korean Leaf Lettuce Cultivars

Abstract

<jats:p>The principal bitter sesquiterpene lactones (BSLs; latucin, 8-deoxylactucin, and lactucopicrin) in six red and four green-pigmented leaf lettuce (<jats:italic>Lactuca sativa</jats:italic> L. var. <jats:italic>crispa</jats:italic> L.) cultivars were identified and quantified using high-performance liquid chromatography, proton nuclear magnetic resonance, and liquid chromatography–mass spectrometry and the contribution of each to the overall bitterness was determined. The concentration of each BSL and the total varied significantly among cultivars and there were significant differences resulting from leaf color (green versus red) and morphology (cut versus curled leaves) with red and curled leaf cultivars having higher BSL concentrations. The concentrations of lactucin, 8-deoxylactucin, and lactucopicrin ranged from 2.9 to 17.2, 2.8 to 17.1, and 8.8 to 36.1 μg·g<jats:sup>−1</jats:sup> dry weight, respectively, with the total concentration ranging from 14.6 to 67.7 μg·g<jats:sup>−1</jats:sup>. Bitterness of the cultivars was assessed using a bitter activity value calculated using the concentration and bitterness threshold value for each BSL. Lactucopicrin was the primary contributor to bitterness as a result of its concentration and lower bitterness threshold; its relative proportion of the total bitterness activity value across all cultivars was over 72%. The concentration of individual BSLs differed with leaf location on the plant (i.e., basal, midstalk, and flower stalk). The concentrations in lactucin, 8-deoxylactucin, and lactucopicrin in flower stalk leaves were significantly higher (i.e., 2.9, 12.4, and 5.4 times, respectively) than in basal leaves, with the concentrations increasing acropetally. Genetic differences among cultivars and with leaf location on the plant contribute to the wide range in bitterness in lettuce.</jats:p>

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

“…It is usually grown for its leaf, but sometimes for its stem and seeds. In Korea, lettuce is mainly consumed as a salad dish or eaten with sandwiches and meat [3]. In recent years, consumers’ interest in lettuce has increased dramatically due to its attractive visual quality, minimum microbial load, and presence of nutritionally important phytoconstituents [1].…”

“…In recent years, consumers’ interest in lettuce has increased dramatically due to its attractive visual quality, minimum microbial load, and presence of nutritionally important phytoconstituents [1]. Moreover, lettuce contains several bioactive phytochemicals including, anthocyanins [4], phenolic acids [5, 6], flavonoids [5, 7], carotenoids, folate, ascorbic acid [8], and sesquiterpene lactones [3, 9]. In addition, lettuce plants did show potent allelopathic activity [10].…”

Perception of bitterness, sweetness and liking of different genotypes of lettuce

“…It is widely believed that this bitterness can be counteracted by sweetness (Bartoshuk, 1975;Keast and Breslin, 2003); an improvement in flavour is therefore likely to be a consequence of manipulating both factors. Although sensory perception of individual sugars (Pangborn, 1963) and SLs (Price et al, 1990;Seo et al, 2009;Sessa et al, 2000) has been previously assessed and sensory perception is well established in the case of sweet compounds, assessment of SL bitterness is sometimes contradictory and has not been considered with regards to tastant mixture suppression.…”

Insights into the Sesquiterpenoid Pathway by Metabolic Profiling and De novo Transcriptome Assembly of Stem-Chicory (Cichorium intybus Cultigroup “Catalogna”)

“…Consistently, the contents of Lc-like compounds showed positive correlation with bitterness in leaves of C. intybus sugarloaf, witloof and radicchio (Price et al, 1990; Peters and van Amerongen, 1998; Poli et al, 2002) and DHLc contents strongly correlated with root bitterness (Hance et al, 2007). Lp is one of the most bitter among chicory STLs (van Beek et al, 1990) and Lp-like molecules are strongly related to bitterness in other Asteraceae species, such as lettuce ( L. sativa ) and endive ( C. endive ) leaves (Seo et al, 2009; D'Antuono et al, 2016). Finally, a recent survey on endives proposes that bitterness depends on the balance between STL and phenolic contents and that the different compounds within these two categories can affect the trait both individually and in a complex manner (D'Antuono et al, 2016).…”