Citrus natsudaidai

Scope: Direct measurement of natsumikan first-press juice (Nihon Kankitsu Kogyo K.K., Yawatahama factory, batch produced in mid-March)

Note: A 1962 analysis. Note that the content differs by more than twofold between pressing stages (1st vs. 2nd press).

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.

Scope: Part-by-part analysis of 1 sample of natsumikan (from Yugawara). The fruit was quartered and divided into peel and fruit; of the peel, the outer 1/3 was taken as flavedo and the remaining 2/3 as albedo. Separated by thin-layer chromatography and quantified by fluorescence.

Note: This is the distribution of the amount of naringin, regarded as a bitter substance, not a sensory evaluation of bitterness (the main text treats naringin as one of the bitter substances and states that removing it is important in making marmalade). The part-by-part values are 1 point each, and the number of fruits and replicates are not described in the main text. Another study of the same natsumikan (Bessho et al. 1964) gave about 1300 mg% for albedo and segment membrane and about 360 mg% for the outer skin (flavedo) by a colorimetric method; the order is the same but the numbers differ.

Scope: Part-by-part analysis of 1 sample of natsumikan (from Ehime). The division of parts is the same as in Morohoshi and Sugawara (1971). Quantified by a color development method as total limonoids in limonin equivalents.

Note: This is the amount of limonoids (bitter substances mainly limonin), not a sensory evaluation of bitterness. The content is total limonoids, not limonin alone. Unlike the distribution of naringin (higher in the albedo and segment membrane than in the flavedo), limonoids are higher in the flavedo than in the albedo and segment membrane, and highest in the seeds. The color development is unstable, measurement was made within 3 minutes after color development, and the recovery of added amounts is stated as ±10%.

Scope: Natsumikan juice squeezed with a reamer-type test juicer, quantified by high-performance liquid chromatography. Harvested from December 28 to May 8. The table labels the cultivar Natsudaidai, while the main text calls it natsumikan.

Scope: Fruit collected from February to March from 1 natsumikan tree at an orchard in Matsuyama, Ehime Prefecture. Each part was finely cut and ground with 5 times its volume of water, the filtrate after heating for 30 minutes in a boiling bath was quantified by Nakabayashi's modified Davis method (colorimetry at 420 nm).

Note: This is the distribution of the amount of naringin, regarded as a bitter substance, not a sensory evaluation of bitterness (the main text describes the bitterness of natsumikan as due mainly to naringin). Differences between fruits were large, with a range of 1.5 to 1.8 times in the juice. In fruit harvested on April 6, the albedo (869 mg%) and segment membrane (978 mg%) were lower, and the amount fell sharply outward from the albedo and segment membrane (a mean of 5 fruits; the author says it is not certain without increasing the number of samples). Fukutani and Miyamoto (1983) point out that the colorimetric method also picks up other flavonoids and so gives higher values than HPLC.

Scope: Fruit from 1 natsumikan tree at an orchard in Matsuyama, Ehime Prefecture. The juice sacs of the flesh, with the segment membrane removed, were divided into the stalk, central part and tip, and quantified by the modified Davis method. The juice was withdrawn with an injection needle.

Note: This is the distribution of the amount of naringin, not a sensory evaluation of bitterness. The author considers that bitterness could be removed almost completely by removing naringin from the stalks and membrane without moving it into the juice part, and conjectures that for peeled flesh, removal from the dorsal side would be more effective than from the ventral side (a conjecture, not confirmed by experiment). The concentration values are by a colorimetric method.

Scope: The introduction of a production test of canned natsumikan in syrup (Nomura et al. 1963). No measured values underlying the proportion are shown in the main text.

Note: The "80% and 20%" is the author's rough estimate, and its source or measurement is not described in the main text. It is not a proportion based on sensory evaluation of bitterness. It is an estimate from 1963.

Scope: Natsumikan grown on the grounds of the Faculty of Agriculture, Yamaguchi University. The peel, segment membrane and seeds were dried and ground, extracted with benzene, and the weight of the precipitate separated with ether was taken as limonoids (from September 1962 to April 1963).

Note: This is a research note; limonoids were measured by the weight of the precipitate, and the composition is unconfirmed (mainly limonin). The result that limonoids in the segment membrane increase with ripening runs opposite to later reports by thin-layer chromatography and HPLC (Hashinaga and Ito 1983, Fukutani and Miyamoto 1983: limonoids in each part decrease as the fruit ripens), and this may be due to the difference in measurement method (precipitate weight method). The author states that values were disturbed from January 1963 onward by frost damage.

Scope: Flesh (juice sacs) of natsumikan from Hiroshima. It was divided into the outer, central and middle parts of the flesh and the juice-storing and stalk parts of the juice sacs, and the naringin dissolving out in a short soak in water and the total naringin were measured by the modified Davis method.

Note: This is the distribution of naringin amount, not a sensory evaluation of bitterness. In fresh fruit, about 1/3 of the total naringin in the juice-storing part and about 1/4 in the stalk part dissolved out in a short soak in water, and after freezing about 2/3 in the juice-storing part and about 1/3 in the stalk part dissolved out. The point that the stalks of natsumikan juice sacs hold a high concentration of naringin agrees with Bessho et al. (1964, about 1.4% in the stalk). The numbers were confirmed in Tables 7 to 9 and the main text. The amounts dissolved from the segment membrane (290 and 219 mg/100 g) are values from separate tests in Table 7 and Table 9, and are the amounts that dissolve when the membrane and flesh are soaked briefly in water, not content.

Scope: 7 trial marmalades (A to G) made from natsumikan flavedo and 2 commercial products (H and I). The main text says "10 products" but the table has 9. Boiled down to a sugar content of about 70% with a mix of flavedo 4, juice 5, pectin extract 5 and sugar 10. 20 panelists in their 20s (2 men and 18 women) evaluated bitterness, peel hardness, color, aroma and overall on a 5-point scale. The direction of the bitterness score and statistical testing are not in the original.

Note: The main text does not state the direction of the bitterness score (whether a higher score means more bitter or less bitter). Because the sample with a high overall score also has a high bitterness score (G: bitterness 3.65, overall 3.45), it can be read as higher being the more favorable side, but this cannot be confirmed. There is no statistical test, and the differences are only a comparison of means. The main text says 10 products, but the tables (Tables 3 to 5) have only 9 (A to I). The naringin amount is 60 to 75 mg% in the trial products and 75 and 76 mg% in the commercial products, not a large difference.

Scope: 8 samples of canned natsumikan (experiment 3, 3 months after manufacture). Combinations of ordinary peeling and cold-acid peeling, Sankyo naringinase and Kumitanase, and the addition method and the soaking method. 7 panelists ranked the bitterness, the ranks were converted to normal scores, and analysis of variance was performed (14 blocks, 7 replicates).

Note: The significant combinations were confirmed from the main text (B-D and C-D at 1%; A-B, B-E, C-E, D-G and D-H at 5%) and from the adjusted means in Table 8 (the 5% least significant difference is 0.78, and 1% is 1.10). The differences from the no-addition group with the same peeling method and the same enzyme (C versus A, E versus D, F versus D, H versus G) are not significant. The adjusted means (+ is more bitter) were A 0.29, B -0.55, C -0.40, D 0.71, E 0.38, F -0.04, G -0.13 and H -0.28. Regarding E and F being judged more bitter than G and H, the author thinks that because G and H had less acid, the panelists were misled about the bitterness by the sourness. The author's summary generalizes this as "an effect of enzymatic debittering is recognized". In the tasting in experiments 1 and 2, the groups with addition were less bitter than those without, and 2B, 2C, 3B and 3C of experiment 1 are described as tasting almost not bitter, but this is a description of tasting with no number of people or method stated.

Scope: A standard limonoid solution obtained as about 1 g from 400 g of dried natsumikan peel was treated with a 1% aqueous solution of each enzyme preparation at 20°C for 20 hours, and the dilution factors at which bitterness was no longer perceived were compared.

Scope: Natsumikan from Hiroshima. Segments with the peel removed and divided, either whole or with the membrane removed, were stored at -20°C for 10 days, and bitterness was compared by the paired comparison method and also evaluated on a scale from -4 (not bitter) to +4 (extremely bitter). For samples with the membrane, the flesh was tasted after removing the membrane while still frozen.

Note: The results are for frozen flesh, not for raw natsumikan flesh or for eating it with the membrane. The scores come out low because the samples were compared together with strongly bitter ones (in another pair in the same table, almost the same material with the membrane removed was rated 2.6 and described as a strong bitterness unfit for general eating), so they should not be read as absolute values. The number of judgments is shown in the table as 14, and the number of panelists is not in the main text. As for how freezing increases bitterness, the author states that it is because naringin dissolved out on thawing becomes locally concentrated on the flesh surface.

Scope: 60 g of natsumikan flesh from Ehime (outer skin and segment membrane removed by hand) was put in a plastic bag and immersed in a hot water bath at each temperature for 30 minutes, the juice was squeezed out, and naringin and water-soluble pectin were quantified.

Note: There was no sensory test of bitterness, and "perceived as more bitter" is the author's presumption from the increase in naringin in the juice. The heating was 60°C for 10 minutes (at 70°C or above the juice sac membrane becomes fragile and the juice cannot be withdrawn). This experiment partly disputes the earlier explanation that bitterness increases on heating (that 40 to 70% of the naringin is in an insoluble or bound form that becomes soluble on heating). The same report states that more than 90% of the amount after heating dissolves out just by grinding, and that the portion that becomes soluble on heating is unexpectedly small (a 6 to 8% increase).

Scope: Enzyme treatment experiments and taste tests (including factory field trials) using natsumikan first-press and second-press juice

Note: This is a source that reached sensory evaluation, not just chemical analysis, by directly measuring the time to bitterness disappearance through taste tests (sensory). It also reports that if the reaction time is too long, discoloration, aroma deterioration, and pulp separation occur.

Scope: Naringin amount by soaking time in water for the flavedo, and the albedo and segment membrane, of natsumikan (from Yugawara). Under 3 conditions (2% salt water, running water, standing water), 2 samples each were measured at 30 minutes and 1, 2, 3, 12 and 24 hours.

Note: This is a measurement of naringin amount, not a result of people evaluating bitterness after soaking in water. The way of cutting (strips for the flavedo, fine chopping for the albedo and segment membrane) affects the speed of dissolution, so it should not be applied as is to thick cuts or whole peel at home. The author describes the difference by type of water as small.

Scope: 10 g of natsumikan flavedo (from Yugawara) was wrapped in gauze, boiled for 15, 30, 45, 60 and 90 minutes, and naringin was quantified. Compared with and without 1 hour of soaking in water. Hardness was measured with a Kiya-type hardness tester.

Scope: The flavedo, and the albedo and segment membrane, of natsumikan (from Ehime) were soaked in water and boiled by the same methods as in the previous report (Morohoshi and Sugawara 1971), and the remaining limonoid amount (as limonin) was measured.

Scope: Canned natsumikan (M to L grade) in syrup from Arida District, Wakayama Prefecture. The segment membrane was removed by acid and alkali treatment with 0.6 to 0.7% hydrochloric acid and sodium hydroxide, washed in water, and packed. The enzyme was added to each can by the addition method, and the cans were sterilized at 65°C for 30 minutes or similar and stored. Naringin in the flesh and the liquid of cans 3 months after manufacture (1 month in experiment 2) was quantified by the modified Davis method.

Note: These are results of measuring the amount of naringin (the sensory evaluation of bitterness is treated as a separate claim). The enzyme preparations were commercial products of the time, and their effectiveness differs by type. Preparations with high pectinase activity made the syrup cloudy white, and the flesh sometimes became slightly softer after 6 months of storage. Fukutani and Miyamoto (1983) point out that the colorimetric method (Davis method) gives higher values than HPLC. The naringin amount of the no-enzyme controls (about 30 to 54 mg%) differs with the can conditions.

Scope: Canned natsumikan in syrup. The peeled and washed flesh was soaked overnight in an enzyme solution made with 0.4 to 0.5% enzyme in warm water (50°C) of the same weight as the flesh, then washed in water and packed. Compared with the addition method (experiments 2 and 3).

Note: The bitterness for the soaking method in experiment 2 is a tasting description, and the only numerical sensory evaluation is G versus H in experiment 3. The soaking method had a higher rate of broken flesh than the addition method (in Table 9, whole fruit was 92% for the addition method and 69% for the soaking method, and broken flesh 8% for the addition method and 31% for the soaking method), and the raw-material yield was also better for the addition method. The author states that the addition method has the advantage that the time of enzyme action is not limited, and that the remaining enzyme acts during storage.

Scope: Canned natsumikan in syrup (No. 5 can, 250 g of flesh, 120 mL of syrup at 55°Bx). Flesh whose segment membrane had been removed by warm acid and alkali soaking (about 1%, 40°C) was soaked in the enzyme solution, washed in water, packed in cans and sterilized at 85°C for 30 minutes. The naringin in the flesh and syrup 1 month after canning was quantified by the modified Davis method.

Note: This is a measurement of naringin amount, not a sensory evaluation of bitterness. Tsusaka (1965) reported that overnight soaking (in warm water at 50°C, not kept warm) did not reduce naringin (36 to 36 mg%), so the results for the same soaking method differ with temperature, enzyme and pectinase activity. The author states that sugar greatly hinders the action of the enzyme (80% or more at the sugar concentration of canned fruit in syrup) and that the enzyme power actually usable is only about 20% of its potency, noting an economic problem (the table of sugar inhibition values is omitted).

Scope: Canned natsumikan. Compared: groups with heat- and acid-resistant naringinase (Tanabe Seiyaku) added at 0.5 g per can and pH adjusted with sodium citrate (A) and without adjustment (N), under different sterilization conditions. Cans were opened immediately after sterilization and at 1 day, 1 week, 2 weeks, 1 month and 5 months.

Note: This is a measurement of naringin amount, not a sensory evaluation of bitterness. It is a process study of the relation between the residual enzyme activity after sterilization and the naringin amount, and the conditions are those of can manufacture, not home cooking. The values are read from a figure, and the main text gives about 10 mg%.

Scope: An account in official materials from Hagi City, Yamaguchi Prefecture