persimmon tannin (kaki-tannin)
compound class / compound-kaki-tannin
カキタンニン
Persimmon tannin (kaki-tannin) is a condensed tannin (proanthocyanidin) that accumulates in high concentration in persimmon fruit's "tannin cells". In its soluble form, it produces strong astringency, but when it becomes insoluble through the action of enzymatically generated acetaldehyde and other mechanisms, it ceases to produce an astringent sensation. A type of tannin.
On this page (8 sections)
Reading the bitterness
The astringency felt in persimmon fruit is caused by a soluble tannin called kaki-tannin. This astringent component is a condensed tannin (proanthocyanidin) that accumulates at high concentration in a specialized cell type called the 「タンニン細胞」 (in translation: "tannin cell") within the flesh of the persimmon. It is also a type of tannin in the broader sense. Kaki-tannin is positioned as an astringent compound. In the scientific literature on persimmons, the concentration of this soluble tannin is described as the fundamental mechanism that determines the intensity of astringency.
The disappearance of astringency through 「渋抜き」 (in translation: "de-astringing") is attributed to kaki-tannin changing from a soluble to an insoluble form. Acetaldehyde generated enzymatically in the persimmon's flesh renders the soluble tannin insoluble, and as a result, the astringent sensation is no longer felt. However, the actual molecular structure of the tannin after insolubilization remains unresolved in the related research.
There are reports concerning the concentration threshold at which astringency is perceived. In a taste test using a 7% glucose + 7% fructose solution with tannic acid added, many test subjects perceived astringency at tannic acid concentrations of 0.10% or above, and in persimmon juice as well, a tannic acid concentration of 0.10% was identified as the threshold at which astringency begins to be perceived. However, a report from another prefecture cites a value of 0.05% or below as the standard for perceiving no astringency; because the measurement context and reference standards may differ, this is noted separately as a different figure.
When a de-astringed persimmon is heated, 「渋戻り」 (in translation: "re-astringing") is observed, in which the soluble tannin content increases again. When paste from water-de-astringed 「伊自良大実」 (Ijirao-daimei) persimmon was heated for 40 minutes under boiling, the re-astringing amount reached 179 mg/100ml, and when paste from alcohol-de-astringed 「刀根早生」 (Tonene-wase) persimmon was similarly heated, it reached 239 mg/100ml, according to reports. In addition, when 「西条」 (Saijo) persimmon paste was boiled at 100°C for 40 minutes, soluble tannin content reached 111.33±1.39 mg/100g; in 60 minutes it reached 178.30±4.59 mg/100g. With pressurized heating at 121°C, it reached 295.44±3.93 mg/100g in 4 minutes and 465.99±3.64 mg/100g in 20 minutes. Pressurized heating resulted in larger re-astringing amounts than boiling, according to reports. However, the mechanism itself—why the soluble tannin content increases upon heating—is not explained in detail in these sources.
Sources for this overview
柿の脱渋に関する一考察(第2報) タンニンの不溶化及びそれに関与する酵素活性の変動
Checked for this overview: Used to support the basic statement that the astringent compound in persimmon is kaki-tannin. / Used to support the de-astringing mechanism of insolubilization by acetaldehyde. / Used to support the astringency threshold of 0.10% from taste testing.
Checked for this overview: Used to support the explanation of high-concentration accumulation in tannin cells. / Used to support the positioning of this as a condensed tannin (proanthocyanidin). / Used to support the statement that insolubilization is a trait associated with acetaldehyde.
柿の新規加工技術に関する研究(加熱時に渋戻りを起こす脱渋渋柿への防止加工技術に関する研究)
Checked for this overview: Used to support the concurrent citation of the alternative standard of 0.05% or below. / Used to support the re-astringing amounts of 179 mg and 239 mg by cultivar.
Checked for this overview: Used to support the detailed re-astringing amounts for different heating conditions.
Follow the connections
persimmon tannin (kaki-tannin) →are key astringent compound…→ Persimmon (kaki)
persimmon tannin (kaki-tannin) →is a type of→ tannins →can elicit→ astringency
Structured claims — open a section to read each claim's confidence, evidence and limits
Composition and content (3)
Note: Positions kaki-tannin as a condensed tannin (proanthocyanidin) that accumulates in the tannin cells of persimmon fruit.
Show data
compound-kaki-tannin —is_a_type_of→ compound-tanninsScope: Gifu Prefecture-grown 「伊自良大実」 (Ijirao-daimei) (water-de-astringed) and 「刀根早生」 (Tonene-wase) (alcohol-de-astringed), frozen paste, boiling for 40 minutes, tannic acid quantification by Folin-Denis method.
Note: Kamiyama and Kashima (Gifu Prefecture Food Science Research Institute Report, fiscal year 2008).
Show data
compound-kaki-tannin —has_measured_content_in→ "When paste from water-de-astringed 「伊自良大実」 (Ijirao-daimei) persimmon was heated for 40 minutes under boiling, the re-astringing amount (soluble tannin content) reached 179 mg/100ml. When paste from alcohol-de-astringed 「刀根早生」 (Tonene-wase) persimmon was heated under the same conditions, it reached 239 mg/100ml (both control sections without additives)."Scope: 「西条」 (Saijo) persimmon paste, experiment conducted at Shimane University (2021).
Note: Tsurunaga, Onda, and Takahashi (2021).
Show data
compound-kaki-tannin —has_measured_content_in→ "When 「西条」 (Saijo) persimmon paste was boiled at 100°C for 40 minutes, soluble tannin content reached 111.33±1.39 mg/100g FW; when boiled for 60 minutes, it reached 178.30±4.59 mg/100g FW. When pressurized and heated at 121°C, it reached 295.44±3.93 mg/100g FW in 4 minutes and 465.99±3.64 mg/100g FW in 20 minutes. Pressurization resulted in larger re-astringing amounts than boiling."Sensory (2)
Note: The basic framing that the astringent compound in persimmon is called kaki-tannin, and that astringency is caused by the concentration of soluble tannin. Inari & Tomoeda (1992) and Kanzaki (2016) both state this in the same way.
Show data
compound-kaki-tannin —are_key_astringents_of→ ingredient-persimmonNote: From the taste test of Inari & Tomoeda (1992). A report by the Gifu Prefectural Food Science Research Institute (fiscal year 2008) cites, as the threshold below which astringency is not felt, a value of 0.05% (50 mg/100 g) or below from the same research lineage (Inari et al., Gifu Women's University); because the measurement context differs (a taste test versus a threshold value from a separate report), it is recorded alongside as a distinct figure.
Show data
compound-kaki-tannin —has_astringency_threshold_of→ "It was confirmed, by ferric chloride reaction and taste tests, that astringency ceases to be felt once soluble tannin concentration falls to 0.1% or below. In a taste test adding tannic acid to a 7% glucose + 7% fructose solution, most subjects felt astringency at a tannic acid concentration of 0.10% or above, and in persimmon juice as well, a tannic acid concentration of 0.10% was judged to be the concentration at which astringency begins to be felt."Mechanism and receptors (1)
Note: Inari & Tomoeda (1992, full text checked) and Kanzaki (2016, full text checked) independently state the same mechanism, tannin insolubilization by acetaldehyde. However, both papers state that the molecular structure of the insolubilized tannin itself remains unresolved.
Show data
compound-kaki-tannin —has_currently_proposed_mechanisms→ "The mechanism of de-astringing is that kaki-tannin changes from soluble to insoluble. Acetaldehyde generated enzymatically in the persimmon's flesh has the effect of rendering soluble tannin insoluble."