Research note 058 — 2026-09-16
What causes green pepper bitterness, and what eases it?
When green pepper tastes bitter, you might think of soaking it in water, cutting it finely, or cooking it well. For adding egg yolk, there is a trial in which people compared the bitterness. In a sample made by crushing raw green pepper and mixing it with water, the sample with egg yolk added was rated less bitter than the sample with egg white.
On this page (7 sections)
What this page shows
- Green pepper's bitterness is not settled by a single compound name alone.
- A 2012 taste evaluation explained that the combination of quercitrin's astringency and green pepper's characteristic aroma was perceived as bitterness.
- In a 2024 cultured-cell assay, multiple human bitter taste receptors responded to quercitrin, and TAS2R8 recorded high response sensitivity.
- In a sensory evaluation of green pepper liquid, bitterness was rated weaker with egg yolk than with egg white, with fine emulsion particles than with coarse ones, and with yolk denatured by mixing with vinegar than with egg yolk alone. A human evaluation against liquid with nothing added is not shown.
- Trials comparing stir-fried or heat-cooked green pepper are 2 conference abstracts, and they do not show the scores.
Astringency and aroma of a compound, or a receptor's response?
A 2012 research presentation compared a conventional variety with 「こどもピーマン」 (in translation: "kodomo piman," a child-friendly pepper), and identified one of the compounds found only in the conventional variety as quercitrin. The presentation text describes the isolated quercitrin itself as 「渋味」 (in translation: "astringency"), and explains that the astringency of quercitrin, combined with the aroma of 2-isobutyl-3-methoxypyrazine, was perceived as green pepper's bitterness.
Scope: Juice extraction, compositional analysis, and taste evaluation of a conventional cultivar and 「こどもピーマン」 (Kodomo Piman).
Note: On the product-release page, the number of tasters, scale, concentration, and statistical values for the taste evaluation are not given. This is not treated as the sole bitterness mechanism for green pepper in general.
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ingredient-green-pepper-ja —has_perceived_bitterness_associated_with→ (the claim sentence above)A different 2024 presentation added quercitrin to cultured cells into which 25 types of human bitter taste receptors had been introduced. Multiple receptors responded, and TAS2R8 showed high response sensitivity. This is not an evaluation of people eating green pepper, but the response of cells into which the receptors were introduced.
Scope: Fluorescence and luminescence methods in which quercitrin was administered to cultured cells expressing human bitter taste receptors.
Note: A joint research release by a company and a university; a peer-reviewed paper has not been confirmed. Cell response is not equated with the bitterness intensity a person experiences when eating.
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compound-quercitrin —activates→ receptor-tas2r8The two presentations differ in both what was compared and how it was measured, so they cannot be directly ranked against each other. The evaluation of tasting a food and the response of cells to a single compound need to be read separately.
People compared egg yolk and egg white
A 2016 presentation used 「ピーマン液」 (in translation: "green pepper liquid"), made by crushing raw green pepper and mixing it with water at a ratio of 1 to 3. When 20 researchers rated the strength of bitterness on a 7-point scale, the sample with egg yolk added had a significantly higher bitterness-reducing effect than the sample with egg white added.
Scope: Green pepper liquid evaluated by 20 Kewpie researchers (12 men, 8 women).
Note: Figure 1 in the corporate-release abstract shows mean values, standard deviations, and significant differences at the 5% level, but the amount added and exact numerical values are not given. This is not a direct comparison of a cut green pepper dish.
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ingredient-green-pepper-ja —has_perceived_bitterness_suppressed_by→ (the claim sentence above)The same presentation also compared the emulsion state of egg-yolk mayonnaise. A sample made into fine particles equivalent to factory production was rated less bitter than a sample made into large particles equivalent to homemade production. Further, acid-denatured egg yolk — made by mixing egg yolk with vinegar and leaving it for about one day — had a higher bitterness-reducing effect than adding egg yolk alone.
Scope: A comparison of egg-yolk-type mayonnaise, varied only in emulsion state, added to green pepper liquid.
Note: Figure 2 in the corporate-release abstract shows mean values, standard deviations, and significant differences at the 5% level, but the particle size, amount added, and exact numerical values are not given. This is not a comparison of commercial product brands.
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ingredient-green-pepper-ja —has_perceived_bitterness_affected_by→ (the claim sentence above)Scope: A 7-point sensory evaluation by 20 panelists of acid-denatured egg yolk and egg yolk added to green pepper liquid.
Note: Figure 3 in the corporate-release abstract shows mean values, standard deviations, and significant differences at the 5% level, but the formulation of egg yolk and vinegar, the amount added, and exact numerical values are not given. This is not a recommendation for a home procedure of letting it sit for about 1 day.
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ingredient-green-pepper-ja —has_perceived_bitterness_suppressed_by→ (the claim sentence above)What people tasted here was green pepper liquid, not a stir-fry or salad of cut green pepper. The mayonnaise's product name and the amount added are not shown. The result is grounds for trying a seasoning that includes egg yolk, but it does not guarantee the same difference on a home-cooked plate.
Every comparison was between two things that were added; a human evaluation against green pepper liquid with nothing added is not shown. The rating by 20 researchers was confirmed in a conference presentation summary carried in the company's news release, and it is not a peer-reviewed paper.
| Comparison | What people rated | Boundary when reading this |
|---|---|---|
| Egg yolk and egg white | Egg yolk had the higher bitterness-reducing effect | Compared in green pepper liquid |
| Large and small emulsion particles | Smaller particles had the higher bitterness-reducing effect | Particle size and amount added not confirmed |
| Egg yolk and acid-denatured egg yolk | Acid-denatured egg yolk had the higher bitterness-reducing effect | Not a recommendation to leave it for about a day at home |
Comparisons in cooked dishes
Trials closer to an actual dish are 2 conference abstracts. In a 2021 abstract, 50 g of stir-fried green pepper seasoned with 7.5 g of deep-roasted sesame dressing was rated significantly less bitter by 20 panelists than a control seasoned with an equivalent amount of salt. The control matched the salt, but salt also tends to suppress bitterness, so it cannot be said that the effect of salt was removed. What in the dressing worked was not examined.
Scope: Green pepper (50 g stir-fried, and a liquid made by adding an equal amount of water to green pepper, grinding it in a food processor and filtering it). The sensory evaluation was by 20 people, comparing deep-roasted sesame dressing against a control of equivalent salt on stir-fried green pepper. A company's (Kewpie's) own dressing. Limited to a conference abstract
Note: The abstract gives no sensory scores or test method. The control was an equivalent amount of salt, not water, so it is a comparison with the salt matched (because salt also tends to suppress bitterness, it cannot be said that the effect of salt was removed). The abstract states that which part of the dressing (oil, vinegar, egg yolk or sesame) was effective has not been examined. The taste sensing system values are not to be equated with human sensory evaluation. Seasoning with the dressing after stir-frying is close to the situation of adding it afterward to a finished dish. As a conference abstract, it has not been peer reviewed.
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ingredient-green-pepper-ja —has_perceived_bitterness_suppressed_by→ (the claim sentence above)In a 2015 abstract, bitter gourd and green pepper heat-cooked with mayonnaise were rated less bitter than those heat-cooked with edible vegetable oil. The abstract does not give the panel size or the evaluation method, and it does not show results for green pepper separately from bitter gourd.
Scope: Bitter gourd and green pepper. Sensory evaluation of samples heat-cooked with mayonnaise or edible vegetable oil (the number of people and the method are not in the abstract), and evaluation of bitterness by a taste sensing system for the group with mayonnaise and the group without. Limited to a conference abstract
Note: The abstract gives no panel size, statistics or numbers. It describes bitter gourd and green pepper without separating them. The taste sensing system values are not to be equated with human sensory evaluation. The mechanism of adsorption was, at the time of the abstract, a speculation still being confirmed. This is research by a company (a mayonnaise manufacturer). As a conference abstract, it has not been peer reviewed. The samples used mayonnaise at the stage of heat cooking; it was not added afterward to a finished dish.
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ingredient-green-pepper-ja —has_perceived_bitterness_suppressed_by→ (the claim sentence above)The conditions and results of each study that paired green pepper with oil, mayonnaise or dairy can be read in the table on Do oil or mayonnaise soften green pepper bitterness?
If you want to try it in the kitchen
The way of trying it closest to the human evaluation available now is to set aside part of the green pepper and compare a portion paired with egg-yolk mayonnaise against a portion without it. This is not a reproduction of the research formulation, but an editorial suggestion for checking, on your own plate, the balance between bitterness and the overall taste.
If green pepper's aroma is a concern, comparing bitterness alone may not give a consistent answer. Putting bitterness, astringency, and the green, grassy aroma into separate words makes it easier to confirm what has changed. Even if bitterness feels weaker when paired with egg-yolk mayonnaise, it cannot be determined that the aroma moved in the same direction too.
Frequently asked
Does soaking in water remove the bitterness?
The material adopted here does not include a trial in which people compared bitterness while varying how long cut green pepper was soaked in water. The research that made green pepper liquid with water at a ratio of 1 to 3 did not investigate the effect of soaking in water.
Does cutting it finely or cooking it work?
The material adopted here does not include a trial that directly evaluated bitterness by varying only how it is cut or cooked. Trials that compared seasonings on cooked green pepper are the 2 in "Comparisons in cooked dishes" above. The possibility that how the aroma comes out or the texture changes cannot be treated as the same answer as bitterness actually decreasing when measured.
What is not known
- A sensory comparison of bitterness that independently varies the green pepper variety used at home, how it is cut, cooking, and soaking in water has not been confirmed.
- For egg-yolk mayonnaise too, the amount added in cooking is not shown.
- The quercitrin receptor trial is a conference presentation by a company and a university, and the test conditions of a peer-reviewed paper cannot yet be confirmed.
Related: green pepper / quercitrin / TAS2R8 / TAS2R38
Related topic hub: Bitter taste receptors
Related research notes: A Dislike of Broccoli Might Be Genetic / Rereading Kitchen Prep Through Measured Bitterness
Source ledger: the source ledger
How to cite this page
Aoki, M. (NIGAMI LAB) (2026). What causes green pepper bitterness, and what eases it?. https://nigamilab.com/en/notes/green-pepper-bitterness/
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