Research note 057 — 2026-09-16
When lettuce tastes bitter, does dressing change it?
You take a bite of lettuce and it is more bitter than expected. Does dressing change how it tastes? In a conference abstract that directly includes lettuce, adding a developed dressing weakened bitterness in a sensory evaluation by people. A seasoning that includes vinegar is a candidate worth trying.
On this page (7 sections)
What this page shows
- One conference abstract records that, across a sensory evaluation of four vegetables including lettuce, bitterness weakened when a developed dressing was compared with no dressing.
- In an instrumental measurement of filtered, crushed lettuce, vinegar — among the dressing ingredients tested — gave a particularly large reduction in bitterness.
- For endive, in the same family as lettuce, all six people who used an acidic, non-oil shiso dressing chose the option describing bitterness as weaker.
- The same paper also shows why. The latex of the leaves is rich in a weakly bitter compound that turns into strongly bitter lactucopicrin while chewing with saliva, and the acid in the dressing suppresses that change: chewed with water, the strongly bitter form reached 45.5%; chewed with dressing, 3.9%.
First, how people tasted lettuce
A 2021 conference abstract added a developed dressing to lettuce, tomato, cabbage, and broccoli, and compared bitterness, astringency, and a green, grassy smell. Alongside instrumental measurement, it also ran a sensory evaluation in which people tasted the vegetables with and without the dressing, and records that this sensation weakened. Of the four vegetables, the effect was largest for lettuce.
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)This is direct evidence that "lettuce's bitterness can be affected by seasoning."
The vinegar result was measured by instrument, not by people
The same research added water to lettuce, crushed it, and filtered the result; egg yolk, cooking oil, vinegar, and carrot purée were then added separately to the filtrate. When compared on a taste sensor (an "electronic tongue"), the reduction in bitterness was particularly large for vinegar.
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)An important boundary sits here. What people tasted was the vegetable with a developed dressing added; people did not compare lettuce with only vinegar added. It cannot be read as "vinegar alone makes it just as easy to eat" or "the balance with sourness also improves." Vinegar is a clue for thinking about the mechanism, not a finished household procedure.
| Comparison | Subject | What can be read directly |
|---|---|---|
| Developed dressing, present or absent | People evaluating four vegetables including lettuce | Bitterness, astringency, and a grassy smell weakened, with the largest effect for lettuce |
| Ingredients added one at a time | Instrument evaluating filtered lettuce | The reduction in bitterness was particularly large for vinegar |
What a small endive trial shows
A different paper uses endive rather than lettuce. When six people ate leaves harvested that day, all six chose "not much felt at first, but bitterness comes out while chewing." When an acidic, commercially available non-oil shiso dressing was added, all six people chose "the bitterness becomes weaker." Because the direct subject of tasting is different, this cannot be counted as a repeat trial of the lettuce result.
Scope: A sensory test with 6 panelists using endive leaves harvested that day and a commercial non-oil shiso dressing.
Note: A single product, 6 panelists, a fixed comparison order; no mention of blinding or randomization. This is not a direct sensory test of lettuce. 2026-10-21 (expansion stage N5, stage C, batch 2): downgraded from supported to preliminary because of 6 panelists, choice-type answers (no numerical scale), a fixed order of plain then dressing, no blinding or randomization, no inferential statistics, and 1 source only.
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ingredient-endive —has_perceived_bitterness_suppressed_by→ (the claim sentence above)Why it weakens: acid suppresses bitterness forming in the mouth
The core of the endive paper is not the six-person tasting but the measurement of the reason. The latex of endive and lettuce leaves is rich in lactucopicrin 15-oxalate, which is only weakly bitter; strongly bitter lactucopicrin makes up less than 1% of the two combined (endive 0.9%, lettuce 0.6%). Yet when 8 g of leaves were chewed for 30 seconds with water, the strongly bitter form had risen to 45.5% of the total. While chewing and mixing with saliva, the strongly bitter compound is produced from the weakly bitter one. All six people choosing "bitterness comes out while chewing" and this number point to the same phenomenon.
Scope: Horie 2011, Tables 1 and 2. Leaves of endive (Takii Seed) harvested that day. For the chewed material, concentrations in the juice pressed out with a garlic press, n=4
Note: That L forms from LO under neutral to weakly alkaline conditions and is suppressed under weakly acidic conditions was confirmed by buffer extraction (proportion of L 1% or less, 4%, and 9% at pH 5.5, 6.5, and 7.5). The 45.5% seen after chewing cannot be explained by pH alone, and the authors note that the involvement of inorganic ions, enzymes, and microorganisms in saliva remains a topic for future work. (2026-10-21, expansion stage N5 stage C batch 5: Codex's check against the source confirmed that formation during chewing is the authors' inference from comparing different samples, the latex and the chewed material (n=4, number of people chewing not stated), not an experiment that directly followed the formation; lowered from supported to preliminary.)
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ingredient-endive —has_bitterness_generated_by→ (the claim sentence above)Chewed with an acidic non-oil shiso dressing (pH 3.8), the strongly bitter form stayed at 3.9%. The chewed mixture had a pH of 4.6–5.0, and leaves dipped for 3 seconds in 5% acetic acid were kept low in the same way. Buffer extractions showed the same direction: 1% or less at pH 5.5, 4% at 6.5 and 9% at 7.5, so the strongly bitter compound forms under neutral to weakly alkaline conditions and its formation is suppressed under weakly acidic conditions. The authors conclude that what the dressing does is not to mask bitterness but to suppress the formation of the strongly bitter compound in the mouth. Because oil might mask bitterness, an oil-free dressing was chosen for this experiment.
Scope: Horie 2011, Table 2 and the main text. A comparison with the water control chewed at 45.5%, n=4. A non-oil dressing was used to avoid the possibility that fat would mask the bitterness
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ingredient-endive —has_debittering_most_likely_due_to→ (the claim sentence above)Scope: Horie 2011, Figure 1. Endive leaves blended and extracted for 3 minutes with 9 times their weight of 0.1 M phosphate buffer, n=3
Note: When the latex of lettuce and endive is analyzed quickly, L is 1% or less of the total (endive 0.9%, lettuce 0.6%), and the authors caution that L can also form from LO during sample preparation for analysis. (2026-10-21, expansion stage N5 stage C batch 5: Codex's check against the source confirmed that the authors stop at calling formation from LO "suggested" on the basis of observations in buffer (n=3); lowered from supported to preliminary.)
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compound-lactucopicrin —is_derived_from→ (the claim sentence above)For lettuce, the measurement goes only as far as showing that the latex has the same composition; no chewing test or sensory test was run on lettuce itself. The authors write only that they expect lettuce to be alleviated by the same mechanism. This agrees in direction with the conference abstract, where vinegar had the largest instrumental effect.
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 far this goes in the kitchen
If the material available so far is turned into a starting point for the kitchen, there is room to compare, on your own plate, eating bitter lettuce as it is against pairing it with a dressing that includes vinegar. This is not a procedure that promises the same result as the research, but a way of trying it that the material makes available.
Start with a small amount on a separate leaf, and choose whichever you find easier to eat, taking into account not only bitterness but also sourness and aroma. What the research shows as "weakens" and what becomes "a matter of taste" as cooking are separate answers.
One thing follows from the mechanism. The acid works when it is present in the mouth while you chew. In the endive experiment the leaves were chewed immediately after the dressing was added. Adding a vinegar-based dressing just before eating, or chewing together with something sour, fits this mechanism. Whether an oil-only dressing would act the same way was not examined in this study (there was no oil-only control).
Frequently asked
Is it enough to just add vinegar?
The vinegar result comes from measuring filtered lettuce with a taste sensor. It is not a result from people eating lettuce with only vinegar added and comparing how much they liked it. The overall taste, including sourness, needs to be checked on your own plate.
Does washing with water remove the bitterness?
The lettuce research adopted here is not a trial in which people compared washing with water against not washing. Washing time or how the leaves are cut cannot be specified as a procedure for reducing bitterness.
What is not known
- A sensory comparison combining the lettuce variety bought at home, the difference between leaf and core, and the type and amount of dressing is not in the material adopted here.
- The detailed test conditions of the conference abstract also cannot be confirmed. A seasoning that includes vinegar can be treated as a candidate, but it cannot yet be written up as a method that works by the same amount for everyone.
Related: lettuce / endive
Related topic hub: Bitterness, Astringency, and Egumi
Related research notes: Kitchen Prep, Read Through Measured Bitterness / Does any seasoning remove bitterness? — Sugar and salt
Source ledger: the source ledger
How to cite this page
Aoki, M. (NIGAMI LAB) (2026). When lettuce tastes bitter, does dressing change it?. https://nigamilab.com/en/notes/lettuce-dressing/
Each claim card has a stable anchor (#clm-…). The dataset is CC BY 4.0; see the data page. Dataset DOI: 10.5281/zenodo.22739101