Amanatsu (Citrus natsudaidai) is a cultivar selected in Tsukumi City, Oita Prefecture, as a bud sport of natsumikan (natsudaidai), officially named Kawano Natsudaidai. It was included in a Kumamoto comparative analysis as a citrus in the "bitter-type" group containing abundant naringin and limonin.
Amanatsu (official cultivar name: Kawano Natsudaidai) was found in the early Shōwa period as a bud sport of natsumikan in Yutaka Kawano's orchard in Kami-Aoe, Tsukumi City, Oita Prefecture. Compared with ordinary natsudaidai, citric acid decreases earlier and it is described as ready to eat from early March. Other sources give 1935 as the discovery year and 1950 as the registration year, but these specific years could not be confirmed in Oita's official materials themselves.
A 2005–2007 fiscal-year survey by the Kumamoto Prefectural Technology Center of bitter compounds in 8 citrus cultivars described amanatsu (Kawano natsudaidai), together with 「大橘」 (Ōtachibana), Kawachi bankan, and banpeiyu, as 『苦味系』 (in translation: "bitter type"), containing abundant naringin and limonin in juice and peel. Unshu mikan, ponkan, shiranui, and sweet spring were described as 『非苦味系』 (in translation: "non-bitter type"), centered on narirutin and hesperidin.
In the detailed section, bitter limonin compounds were explicitly named in the juice of ponkan, banpeiyu, and sweet spring, but the text did not explicitly mention amanatsu juice. Limonin was described as present in the peel of all 7 cultivars except unshu mikan, while nomilin was detected only in Kawachi bankan peel. The summary classification and detailed description do not fully agree, so both are recorded as stated.
The survey reports no change in bitter-compound content after heating, while odor produced during heating was strongest in unshu mikan and weakest in amanatsu among 8 cultivars. This odor difference concerns smell and is separate from bitterness strength. Public information mainly concerns whether classifications are present; actual naringin and limonin amounts could not be confirmed.
熊本県産業技術センター / 2008 / government document / full text checked
Checked for this overview: The classification among 4 bitter-type cultivars and its basis was confirmed. / The discrepancy between the summary and detailed limonin descriptions was confirmed. / The distinction between heating-related odor and bitter compounds was confirmed.
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Composition and content (4)
amanatsu (Citrus natsudaidai) is derived from Citrus natsudaidaicontextual
Scope: An account in official materials from Oita Prefecture
Note: Discovered in the early Showa era as a branch sport (bud mutation) of natsumikan (natsudaidai) at Kawano Yutaka's summer-citrus orchard in Kami-aoe, Tsukumi City, Oita Prefecture. Its citric acid drops faster than ordinary natsudaidai, and it is ready to eat from early in the 3rd month (March). The specific year given in other sources — "discovered in 1935, registered as 'Kawano natsudaidai' in 1950" — could not be confirmed in Oita Prefecture's own official materials.
Records that amanatsu (Kawano natsudaidai) was a branch sport discovered in the early Showa era at Kawano Yutaka's summer-citrus orchard in Tsukumi City, that its citric acid drops faster than ordinary natsudaidai, and that it is ready to eat from early in the 3rd month (March).
Limitations: The discovery year is recorded only as "the early Showa era"; the year 1935 given in other sources cannot be confirmed from this primary source alone.
Scope: Kumamoto Prefectural Industrial Technology Center research, 2005-2007 fiscal years, 8-variety comparison
Kawano Natsudaidai, Daibukuro, 「河内晩柑」 (Kawachi Bankan), and Banpeiyu are treated as a 『苦味系』 (in translation: bitter type) containing high levels of naringin and limonin in juice and pericarp, while Unshu mikan, Ponkan, Shiranui, and Sweet Spring are classified as non-bitter type (centered on naringenin and hesperidin). Heat treatment did not change the content of bitter components, but heating odor was strongest in Unshu mikan and weakest in Kawano Natsudaidai.
Limitations: Public information is summary-level only; specific quantitative values (mg% etc.) and analytical method details have not been confirmed from the primary report. Whether the heating odor evaluation was a quantitative sensory assessment or descriptive evaluation could not be confirmed in this survey.
Scope: Kumamoto Prefectural Industrial Technology Center research, 2005-2007 fiscal years, 8-variety comparison
Note: The summary and detailed sections of the source material do not match in their enumeration of varieties; both are recorded as stated.
The summary section of the document states that Kawano Natsudaidai, Daiorange, Kawachibankan, and Banpeiyu 「果汁及び果皮にナリンギン、リモニンを多く含む」 (in translation: "contain much naringin and limonin in juice and peel"). In the detailed section, however, the varieties named as having bitter limonoids in juice are Ponkan, Banpeiyu, and Sweet Spring, with no explicit mention of Kawano Natsudaidai juice. Peel limonin is present in all 7 varieties except Satsuma mandarin. Nomilin is contained only in Kawachibankan (Table 2, in the peel description).
Limitations: Quantitative values have not been confirmed (presence/absence classification only). Tables 1 and 2 (images) have not been checked.
Scope: Naringin in the flesh (juice sacs), segment membrane and peel of Kawano natsudaidai was compared between the portion extracted with water after complete grinding and the total amount obtained by heating after grinding.
Note: This result differs from the earlier explanation (Nakabayashi's theory, cited by Tsusaka 1965) that 40 to 70% of the naringin in natsumikan is in an insoluble or bound form that becomes soluble on heating. Bessho et al. and Manabe et al. (1964, natsumikan) also reported that more than 90% of the amount found after heating dissolved out by grinding alone, with the insoluble or bound form being only a part.
The Japanese summary says "juice and segment membrane", but the main text (p.547), Table 1 and the English abstract (pulp segment) state that no insoluble naringin was found at all in the flesh (juice sacs) and segment membrane, and that all of it was the soluble form (Table 1: flesh 62.3/62.3, segment membrane 1059/1059 mg%). For the peel, the main text says 4.0% of insoluble naringin was present but that it was not clear whether this was a true insoluble form or whether the grinding of the peel was still insufficient; in any case, the author considers that most of the naringin in the fruit appears to be water-soluble. However, Table 1 prints the peel values as soluble 756 mg% and total 726 mg%, which by the footnote formula ((total − soluble)/total × 100) do not give 4.0%, so the source is internally inconsistent.
Limitations: The 4.0% for the peel does not match the values in Table 1, so its treatment is uncertain. "Juice" in the Japanese summary disagrees with "flesh" in the main text, tables and English abstract. This claim follows the main text and tables.
Source: カンキツの苦味に関する研究 (間苧谷徹; 長谷嘉臣; 松本亮司, 1979) · full text checked
Show dataingredient-amanatsu —has_composition→ compound-naringin
amanatsu (Citrus natsudaidai) shows the sensory response The naringin amount in juice pressed from the flesh of Kawano natsudaidai with a manual juicer agreed relatively well with the sensory test of the bitterness of the flesh: at around 50 mg% bitterness was clearly perceived (the limit accepted as a commercial product), and at 63 mg% or more many panelists judged it unsuitable for eating. The mean for fresh fruit was about 24 mg% (ordinary bitterness), and the strongly bitter frozen fruit was about 74 mg%.preliminary
Scope: Fresh and frozen fruit of Kawano natsudaidai (flesh of varying degrees of bitterness). A panel of 12 judged the flesh as "ordinary, clearly bitter, or extremely bitter (unsuitable for eating)" and this was matched against naringin in pressed juice (modified Davis method).
Note: The panel was 12 people, which the author also notes is small. Read from Figure 4, in a sample with about 20 mg% naringin all 12 panelists judged it "ordinary"; at about 28 mg%, 10 judged it ordinary and 2 clearly bitter; in samples at about 45 to 50 mg%, 8 to 7 judged them clearly bitter; and at about 70 mg% all 12 judged it extremely bitter (read by eye from the figure, so the horizontal axis values are approximate). This is a correspondence between the bitterness of the fruit itself and naringin in pressed juice, not an experiment that shows a threshold concentration of naringin.
The main text states that although the panel of 12 is rather small, the naringin content agreed relatively well with the sensory results, that bitterness was clearly perceived at around 50 mg% (the limit accepted as a commercial product), and that at 63 mg% or more many judged it unsuitable for eating.
Limitations: The panel was small (12 people). The naringin values are those in pressed juice, not the amount in the whole flesh. This is a correspondence for these samples and this panel, not a threshold for pure naringin.
Source: カンキツの苦味に関する研究 (間苧谷徹; 長谷嘉臣; 松本亮司, 1979) · full text checked
Show dataingredient-amanatsu —has_sensory_response→ (the claim sentence above)
amanatsu (Citrus natsudaidai) — perceived bitterness is affected by: The strength of bitterness in the flesh (juice sacs without the segment membrane) of Kawano natsudaidai (amanatsu) did not correspond to the total amount of naringin extracted by completely grinding the flesh, but corresponded to the amount of naringin released by hand pressing (squeezing). Naringin by complete grinding was almost the same in fresh and frozen fruit, 67.3 and 69.9 mg%, but by pressing it differed greatly, 23.7 mg% in fresh and 73.0 mg% in frozen fruit, and the bitterness was normal in fresh fruit and "extremely bitter" in frozen fruit. The author considered that what determines bitterness is the naringin released when the flesh is chewed with the teeth: in fresh fruit, little dissolves from the juice sac membrane (especially the stalks of the juice sacs), which holds much naringin, but when freezing makes the membrane fragile, a large amount dissolves out of the membrane and gives strong bitterness.preliminary
Scope: Flesh (juice sacs without the segment membrane) of Kawano natsudaidai (1 tree aged 17 years; fresh fruit harvested on January 13 and stored at 4°C, and frozen fruit). Naringin in juice prepared from fresh and frozen flesh by complete grinding, pressing and extraction (modified Davis method) was compared with a sensory test of the bitterness of the flesh (12 people for Table 3 and Figure 4, no number given for Table 2; no statistical test).
Note: This is an experiment that measured bitterness by sensory test and matched it against naringin. It is a study of the effect of freezing, not of flesh with the membrane removed or of the effect of cooking. "It comes out of the membrane when chewed" is the author's interpretation and not an experiment that directly measured dissolution from the membrane (the data that all panelists judged even the juice sacs of frozen fruit, rinsed with water, to be bitter and inedible support the interpretation). The samples in this report are Kawano type (corresponding to amanatsu), and it cannot be taken as the same for hassaku or natsumikan. The introduction states that natsudaidai and hassaku become bitter from winter cold damage. (2026-10-21, expansion stage N5 stage C batch 5: Codex's check against the source confirmed that the samples came from 1 tree, there is no statistical test of the sensory results, and the mechanism of dissolution from the juice sac membrane is the author's inference; at the same time "segment membrane" was corrected to the original's "juice sac membrane" and the mg% conversion note was removed; lowered from supported to preliminary.)
Table 4 shows complete grinding (fresh 67.3, frozen 69.9 mg%), pressing (23.7, 73.0), light pressing (15.2, 75.6) and juice within the juice sacs (10.0, 48.1). In Table 2, the naringin measured by pressing was about 20 to 27 mg% in 7 fresh samples and 70 to 78 mg% in 7 frozen samples, and the bitterness was normal in fresh fruit and extremely bitter in frozen fruit. Table 3 shows that all 12 panelists judged even the juice sacs of frozen fruit rinsed with water to be extremely bitter. The summary states that the increase in bitterness of the flesh on freezing seems to be because the juice sac membrane becomes fragile, so that naringin of the membrane has already dissolved into the juice sacs and made the juice considerably bitter, and in addition a large amount of naringin dissolves out of the juice sac membrane (especially the stalks) on chewing with the teeth.
Limitations: The panel for Table 3 and Figure 4 was 12 people, and Table 2 gives no number. There is no statistical test of the sensory results. The sample was frozen fruit, not ordinary cooking of the flesh. The interpretation of dissolution from the juice sac membrane (especially the stalks) is the author's inference.
Source: カンキツの苦味に関する研究 (間苧谷徹; 長谷嘉臣; 松本亮司, 1979) · full text checked
Show dataingredient-amanatsu —has_perceived_bitterness_affected_by→ (the claim sentence above)