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.
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ingredient-lettuce —has_composition→ (the claim sentence above)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.
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ingredient-lettuce —has_composition→ (the claim sentence above)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).
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ingredient-lettuce —has_perceived_bitterness_unchanged_by→ (the claim sentence above)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.
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ingredient-lettuce —has_perceived_bitterness_associated_with→ (the claim sentence above)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.
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ingredient-lettuce —has_perceived_bitterness_suppressed_by→ (the claim sentence above)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.
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ingredient-lettuce —has_perceived_bitterness_suppressed_by→ (the claim sentence above)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.
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ingredient-lettuce —has_e_tongue_bitterness_reduced_by→ (the claim sentence above)