lettuce
ingredient / ingredient-lettuce
レタス / Lactuca sativa
Lettuce in general, including heading and non-heading types. The cut stem surface and core contain bitter sesquiterpene lactones, and a body of research examines changes with light and storage conditions.
On this page (9 sections)
Reading the bitterness
Lettuce's bitterness has been measured as a characteristic that does not disappear even in comparisons of protected cultivation under covers using red-leaf lettuce. In an evaluation by a trained sensory panel, bitterness was the only basic taste to show a 「中程度」 (in translation: "moderate") score, while sweetness, sourness, saltiness, and umami were all 「非常に低い」 (in translation: "very low"). Even comparing 7 simple covered-tunnel treatments — standard poly, diffusion poly, clear poly, UV-A/B-blocking poly, 55% shade netting, among others — many attributes including bitterness showed no significant difference; of 20 attributes, differences by covering material appeared in only 8, such as color intensity and astringency.
So what does the source of bitterness reflect? In a study of 3 red and 3 green lettuce cultivars grown in a greenhouse, 「総合味」 (in translation: "overall taste") ratings by a sensory panel on the day of harvest showed a negative correlation with total sesquiterpene lactone content and with the individual contents of lactucopicrin, caffeoylmalic acid, and chlorogenic acid; samples with lower contents of these compounds are interpreted as having been preferred as having a 「苦味の少ない味」 (in translation: "less bitter taste"). Another study analyzed the cut stem surface of a crisphead cultivar stored at 9℃ for up to 9 days, and identified cichorioside B in the core tissue as the predominant candidate bitter component. However, the latter study did not include a sensory evaluation, and the connection to bitterness perception cannot be confirmed from this source alone.
On the preparation side too, cues for easing bitterness have been reported. A 2021 conference abstract that added a developed dressing to 4 vegetables — lettuce, tomato, cabbage, and broccoli — records that bitterness, astringency, and green/grassy off-flavor were reduced, with the greatest effect seen in lettuce among the 4 vegetables. In the same presentation, egg yolk, cooking oil, vinegar, and carrot purée were added individually to a filtrate made by crushing lettuce with water and filtering it, and compared using a taste-sensing system; the abstract states that the bitterness-reducing effect was especially high for vinegar. However, this is not a result of a person tasting and comparing lettuce with only vinegar poured on it, and because it is a conference abstract, the number of evaluators and the details of the formulation are not known.
The endive paper also offers a perspective on why a dressing weakens lettuce's bitterness. Lettuce's latex contains the same two compounds as endive, and the strongly bitter lactucopicrin makes up only 0.6% of the total. As this compound increases while mixing with saliva during chewing, the dressing's acid suppresses it. The authors expect that this mechanism also applies to lettuce, but no test measured from actually chewing lettuce itself, and no sensory test, has been carried out. What the present material can say goes only as far as this being consistent in direction with the conference abstract's instrumental measurement finding that vinegar's bitterness-reducing effect was especially large.
Sources for this overview
Effect of Light Characteristics on the Sensory Properties of Red Lettuce (Lactuca sativa)
Checked for this overview: In the comparison of 7 covering-material treatments, bitterness scored moderate with no significant difference; only 8 attributes showed a significant difference
Checked for this overview: Negative correlation between 「総合味」 (in translation: "overall taste") scores and STL, lactucopicrin, and other content levels
Checked for this overview: Identification of cichorioside B in the core tissue as a candidate bitter component
Checked for this overview: Addition of a developed dressing to 4 vegetables produced the greatest reduction in lettuce's bitterness / Among individually added ingredients in a lettuce filtrate, vinegar gave the greatest bitterness reduction (instrumental evaluation) / Supports the conference abstract's instrumental measurement finding that vinegar's effect was especially large.
Checked for this overview: Supports the 0.6% figure for lettuce's latex, and the limitation that this is the authors' expectation with no test on lettuce itself.
Other names: Lactuca sativa (la)
Structured claims — open a section to read each claim's confidence, evidence and limits
Composition and content (2)
Scope: A factorial greenhouse trial with 3 red and 3 green lettuce cultivars over 3 cropping seasons: autumn, winter, and spring.
Note: Both fertilizer treatments used microbial products (EM Aktiv and Vital Tricho); this was not a trial varying the application rate of chemical nitrogen fertilizer in steps.
Show data
ingredient-lettuce —has_composition→ "A factorial greenhouse trial combined 3 red and 3 green lettuce cultivars, 2 microbial fertilizers (EM Aktiv and Vital Tricho) applied separately or together, and 3 cropping seasons: autumn, winter, and spring. Lactones (sesquiterpene lactones) accumulated most in the autumn crop. Total phenol content, like lactone content, was highest in autumn, whereas the predominant phenolic acids (chicoric acid and caffeoyltartaric acid) and flavonoids overall were highest in winter. Red cultivars had higher phenol and lactone contents than green cultivars, and 'Carmesi' (red) had the highest lactucopicrin value. EM Aktiv and Vital Tricho applied separately significantly increased phenolic-acid and dihydrolactucopicrin contents; their combined application increased all detected lactones. Separate application did not affect flavonoid content, whereas combined application decreased it."Scope: Crisphead lettuce cultivar 'oasis', Gunma Prefecture, Japan; a single field and a single cropping season.
Note: The authors themselves explicitly state 『官能評価・消費者受容性試験・他品種や他の栽培条件での検証が実用化前に必要』 (in translation: "Sensory evaluation, consumer-acceptance testing, and validation with other cultivars and under other growing conditions are necessary before practical application"). This study includes no sensory evaluation. A connection to perceived bitterness cannot be confirmed from this source alone.
Show data
ingredient-lettuce —has_composition→ "The crisphead cultivar 'oasis' (from the same field in Numata, Gunma Prefecture; sown on April 4, 2022, transplanted on April 27, and harvested on June 16) was stored at 9℃ for up to 9 days (D1, D2, D3, D4, D5, D7, D9). Groups harvested at 4 a.m. and 4 p.m. were compared. High-resolution LC-MS analysis identified cichorioside B as a predominant candidate bitter component in the core tissue at the cut stem surface. Lactucin, 11β,13-dihydrolactucin, and lactucopicrin were also targeted for quantification."Sensory (3)
Scope: Red-leaf lettuce, a single growing season, a simple covered-tunnel field trial in Kansas, USA
Note: A 20-attribute descriptive scale from 0 (none) to 15 (extremely strong), used by a trained panel of 5 (4 women, 1 man, ages 58-77, more than 120 hours of training, more than 2000 hours of sensory-evaluation experience).
Show data
ingredient-lettuce —has_perceived_bitterness_unchanged_by→ "A comparison of red-leaf lettuce under 7 simple covered-tunnel treatments (standard poly, a removable treatment with covering removed 2 weeks before harvest, diffusion poly, clear poly, UV-A/B-blocking poly, 55% shade netting, and open field). Bitterness was the only basic taste to show a 『中程度』 (in translation: "moderate") score (sweetness, sourness, saltiness, and umami were all 『非常に低い』 (in translation: "very low")), but no significant difference was detected among covering materials (only sweetness was significantly higher in the diffusion treatment). Of 20 attributes, significant differences among covering materials appeared in only 8: color intensity, initial crunch, wateriness, dental grittiness, parsley-like aroma, woody aroma, overall sweetness, and astringency."Scope: A factorial greenhouse trial with 3 red and 3 green lettuce cultivars over 3 cropping seasons: autumn, winter, and spring.
Note: The sensory panel was small, with 4 members (2 men and 2 women, agricultural-science students trained in accordance with ISO 8586:2012). Its scale was a 5-point hedonic scale for 『総合味(overall taste)』 (in translation: "overall taste"), rather than a separate measure of 『苦味強度』 (in translation: "bitterness intensity"); the interpretation in terms of bitterness is indirect and based on the paper's discussion.
Show data
ingredient-lettuce —has_perceived_bitterness_associated_with→ "Sensory-panel ratings of 『総合味』 (in translation: "overall taste"), assessed on a 5-point hedonic scale on the day of harvest, were negatively correlated with the contents of total sesquiterpene lactones, lactucopicrin, caffeoylmalic acid, and chlorogenic acid. Samples with lower contents of these compounds had higher (= more favorable) 『総合味』 (in translation: "overall taste") ratings, which the paper interprets as reflecting a 『苦味の少ない味』 (in translation: "less bitter taste")."Scope: A 2021 conference abstract by an author affiliated with Kewpie. Sensory evaluation of 4 vegetables, including lettuce, with and without dressing.
Note: The number of evaluators, cultivar/part, formulation, amount added, scale, and statistical values are not given in the abstract. Reproducibility with an arbitrary commercial dressing and the appropriate amount for home use have not been tested.
Show data
ingredient-lettuce —has_perceived_bitterness_suppressed_by→ "Addition of a developed dressing. The conference abstract states that sensory evaluation of lettuce, tomato, cabbage, and broccoli found bitterness, astringency, and green/grassy off-flavor were reduced, with the greatest effect seen in lettuce."Mechanism and receptors (1)
Scope: Horie 2011, Table 1 and the discussion. Lettuce grown in a vinyl greenhouse in Tsu City, Mie Prefecture, and analyzed on the day of harvest
Note: For lettuce, only the composition of the latex (Table 1) was measured; the reducing effect is the authors' expectation. This is consistent in direction with the conference abstract (Matsumoto et al. 2021)'s instrumental measurement finding that vinegar's bitterness-reducing effect was especially large.
Show data
ingredient-lettuce —has_perceived_bitterness_suppressed_by→ "The dressing's acid (the authors' inference). The latex of lettuce (cultivar Berkeley) also contains the same lactucopicrin 15-oxalate (LO) and lactucopicrin (L) as endive, and L is only 0.6% of the total. As with endive, it is expected that the dressing's acid suppresses the formation of L that occurs as it mixes with saliva during chewing, and that the bitterness is thereby reduced. No test measured from actually chewing lettuce itself, and no sensory test, has been carried out"How processing and cooking change it (1)
Scope: Individual addition of egg yolk, cooking oil, vinegar, and carrot purée to a filtrate made by crushing lettuce with water and filtering it, with instrumental evaluation.
Note: This is not a comparison of a person tasting lettuce with vinegar poured on it. Ingredient concentration, cultivar, part, numerical values, and statistical values are not given in the abstract.
Show data
ingredient-lettuce —has_e_tongue_bitterness_reduced_by→ "Vinegar. In a taste-sensor evaluation where dressing ingredients were added individually to a lettuce filtrate, the bitterness-reducing effect was especially high for vinegar."