A fruit vegetable in the nightshade family. Polyphenols such as chlorogenic acid are considered to be involved in the astringency of the flesh, and Japanese cooking science has examined by sensory testing how perceived astringency changes with steaming, grilling, simmering, sautéing and deep-frying.
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Sensory (5)
eggplant — combined bitter-astringent taste is affected by: Cooking method. Commercially available eggplant was cooked in 5 ways (steamed, grilled, simmered, sautéed, deep-fried), and 14 panelists compared the strength of astringency by ranking test. Astringency was strongest in the steamed eggplant and weaker in the order grilled, simmered, sautéed and deep-fried, with deep-fried the weakest (rank sums: steamed 21, grilled 30, simmered 39, sautéed 54, deep-fried 66; Kendall's W test, significant at the 1% level).supported
Scope: 1 type of commercially available eggplant bought in Kyoto city, cooked as skin-on boat-shaped pieces cut lengthwise into 8 (200 g from 2 eggplants). 14 students and staff of Doshisha Women's College evaluated by ranking test. The term evaluated was astringency; bitterness was not evaluated.
Note: The order of astringency of eggplant by cooking method did not match the order of total polyphenol amount or chlorogenic acid amount (the chlorogenic acid amounts in steamed and deep-fried eggplant were almost the same, 179.6 and 178.9 mg%, yet astringency was strongest in steamed and weakest in deep-fried). The authors infer that oil does not reduce the astringent components but weakens how they are perceived (not measured). Read the fact that sautéing and deep-frying, which use oil, were weaker separately from the inference about the reason.
In the ranks in Table 2, rank 1 (most astringent) went to steamed for 8 panelists, grilled for 5 and simmered for 1, and rank 5 (weakest) went to deep-fried for 10; the rank sums were steamed 21, grilled 30, simmered 39, sautéed 54 and deep-fried 66. The main text states that the strongest astringency was in steaming and the weakest in deep-frying. Total polyphenol amount / chlorogenic acid amount in Table 4 (mg%, as chlorogenic acid) were: raw 189.1 / 136.2, steamed 199.2 / 179.6, grilled 193.8 / 123.7, simmered 240.1 / 167.8, sautéed 224.1 / 148.3, deep-fried 234.4 / 178.9.
Limitations: Astringency was the main rating (the sourness of reagents appears in Table 5); bitterness was not evaluated as a separate item. The eggplants were commercial ones bought in Kyoto city; the cultivar, the number of cultivars and the number of cooking repeats are not given. The component values for simmered eggplant are totals including the cooking liquid; grilled eggplant lost about 43% of its weight, and the discussion says the evaporated water was not replenished at the sensory test (the methods say the eggplant was re-weighed after cooking and the loss made up with distilled water, and do not distinguish samples for measurement from samples for serving). The rank sums are read from the table. The reason for the mismatch between component amounts and astringency is the authors' inference.
eggplant — combined bitter-astringent taste is affected by: Adding edible oil (salad oil) when simmering. Eggplant simmered with oil was judged less astringent than eggplant simmered without it (in a paired comparison of 2 samples by 14 panelists, 3 answered that the one with oil was more astringent and 11 answered that the one without oil was more astringent; significant at the 5% level). There was no difference in total polyphenol amount or chlorogenic acid amount between the two.supported
Scope: Simmered eggplant made by simmering 200 g of commercially available eggplant in 300 mL of second dashi for 10 minutes, then adding light-colored soy sauce and salad oil and simmering for 5 more minutes (the control had no oil). Paired comparison (2 samples) by 14 students and staff of Doshisha Women's College. Astringency was evaluated; bitterness was not evaluated.
Note: The key point is that astringency was perceived as weaker although the components (total polyphenol amount and chlorogenic acid amount) were the same. The components were measured as the total of the pieces and the cooking liquid. There is no comparison with varying amounts of oil.
Table 1 gives the number of panelists who felt the astringency was stronger: 3 for edible oil added and 11 for no addition (significant at the 5% risk level). The main text states that adding edible oil to simmered eggplant weakens astringency. In Table 3, total polyphenol amount / chlorogenic acid amount (mg%) for the pieces, cooking liquid and total of simmered eggplant with oil were 142.0, 112.9 and 254.9 / 74.3, 92.3 and 166.6, and without addition 133.0, 107.0 and 240.0 / 89.8, 78.0 and 167.8; the authors state that no difference was found.
Limitations: 1 cooking run, 14 panelists; the number of cooking repeats is not given. The amount of salad oil added was 2.5 mL (p.120). Only astringency was evaluated; bitterness was not asked about.
eggplant — combined bitter-astringent taste is affected by: chlorogenic acidpreliminary
Scope: A comparison among 6 to 7 eggplant cultivars and lines (including the Nara Prefecture native line 'Yata'). The sensory evaluation was by 16 to 19 panelists, mainly staff of agricultural research institutions, in comparison with the reference cultivar 'Senryo-nigo' (7-point scale from -3 to 3). The correlations are on the means for each cultivar (n=6 for salt pickling and seasoned pickling, n=7 for the others), and astringency was evaluated (bitterness was not evaluated).
Note: The correlations are rank correlations between the means of 6 to 7 cultivars and do not include individual perception or variation within the same cultivar. The author states that the relation between the chlorogenic acid amount of raw eggplant and astringency after cooking needs further study, because the chemical changes of decomposition and oxidation during heating are not understood. The coefficients in the table, such as 0.875 to 1.000 for the flesh, are also written in the main text (the main text gives "0.875 to 1.000").
Table 7 (correlation coefficients between the chlorogenic acid content or total polyphenol content of the raw fruit and astringency after cooking): for chlorogenic acid content in the flesh, salt pickling 0.929*, seasoned pickling 1.000**, agedashi 0.875*, nibitashi 0.536, steaming 0.366 and grilling 0.071; in the peel, salt pickling 0.986*, seasoned pickling 0.886*, agedashi 0.768, nibitashi 0.464 and steaming 0.116. For total polyphenols in the flesh: 0.929*, 1.000**, 0.875*, 0.519, 0.366 and 0.071 (* significant at 5%, ** at 1%; Spearman rank correlation). The main text states that no significant correlation was found for nibitashi, steaming and grilling.
Limitations: These are rank correlations on 6 to 7 points using the mean for each cultivar, so causation cannot be inferred. The seasoned pickling value (flesh 1.000) is a perfect agreement of ranks with n=6. Only astringency was evaluated; bitterness was not evaluated. Among the cooking conditions, the heating time for grilling was adjusted for each cultivar. The components were measured on a separate fruit harvest of 8/15 (15 Aug) and the sensory tests were on separate days in month 7 (Jul) from separate harvests; the correlations are between per-cultivar values.
eggplant — combined bitter-astringent taste is affected by: Cooking method. Astringency ratings differed significantly among cultivars and lines for salt pickling, steaming and grilling, but no significant difference in astringency among cultivars was found for seasoned pickling, agedashi and nibitashi (the coefficient of variation of the astringency rating index was 25.0% for salt pickling and 7.9% for agedashi).supported
Scope: Fruit of 7 eggplant cultivars and lines. Cooking used a mild Japanese-style seasoning. The sensory evaluators numbered 16 to 19, in comparison with the reference cultivar 'Senryo-nigo' (-3 to 3). Astringency was evaluated (bitterness was not evaluated). Steamed and grilled samples also had ponzu or soy sauce poured on just before eating, so this is not a comparison divided by the strength of seasoning.
Note: The authors interpret that seasoned pickling and nibitashi have complex seasoning that makes astringency harder to perceive, and that agedashi has oil that weakens astringency (this is an interpretation, not a comparison that varied the seasoning or the presence of oil). For steaming, the differences in astringency among cultivars were significant, and so were flesh texture and wateriness.
The abstract states that significant differences among cultivars were found in taste evaluation (deliciousness) in all cooking methods except agedashi, and in astringency for salt pickling, steaming and grilling. The main text states that for seasoned pickling, significant differences among cultivars and lines were found in all sensory evaluation items except astringency, and the same for nibitashi; for agedashi, the significant items were flesh texture and oiliness; and for salt pickling the coefficient of variation of the astringency rating index was 25.0% and for agedashi 7.9%. The discussion states that in nibitashi astringency becomes harder to perceive because of the complex seasoning, and, for the small difference in astringency in agedashi, that it is considered due to cooking eggplant in edible oil weakening the perception of astringency (Kurosawa, 1986b).
Limitations: This compares by cooking method whether differences among cultivars are significant; it is not an experiment that directly compared the effects of seasoning or oil. Only astringency was evaluated; bitterness was not evaluated. The oil explanation is a discussion citing Kurosawa (1986b), not an experiment in this paper comparing oil with no oil. A non-significant result does not mean there is no difference (the panels were 16 to 19 panelists).
eggplant shows the sensory response bitternesspreliminary
Scope: A dynamic sensory evaluation of purple eggplant and zucchini boiled or baked for 15, 30 and 45 minutes (as described in the abstract). The abstract does not show which cooking conditions were bitter.
Note: A claim read from the abstract only. The abstract states that the longer chewing counts and eating times were in the baked samples and the briefly cooked samples, so the correspondence between bitterness and cooking method and time must be checked in the full text. If incorporated, do not generalize it as a relation between cooking time and bitterness.
The abstract states that, as a consequence, samples with longer in-oral exposure times were perceived as bitter (eggplant) or sweet (zucchini). It also states that baked samples took more effort to chew, and that chewing counts and eating times were high for briefly cooked and baked samples.
Limitations: Abstract only. The number of panelists, the evaluation method and the numerical bitterness values have not been checked. It is not known under which conditions it was how bitter.
eggplant — combined bitter-astringent taste is affected by: Coexistence of edible oil. When 5% edible oil was added to an aqueous caffeic acid solution (0.6 × 10^-2 mol/L) at a concentration close to the astringency of eggplant and shaken, all 14 panelists answered that the one without oil was more astringent (significant at the 1% level). The astringency with oil was about the same as that of a 0.46 × 10^-2 mol/L solution without oil, and the authors regarded it as weakened by roughly a quarter.preliminary
Scope: A model experiment using an aqueous solution of caffeic acid (a constituent of chlorogenic acid; the authors presume that the astringency of eggplant is caused by its caffeic acid portion). 14 students and staff of Doshisha Women's College. It is not an evaluation of cooked eggplant itself.
Table 5 shows that caffeic acid gave only an astringent, tongue-puckering taste, quinic acid gave sourness, and chlorogenic acid gave astringency and sourness. Table 6 compares a sample of 0.6 × 10^-2 mol/L caffeic acid solution with 5% edible oil added against one without oil; the number of panelists who felt astringency was stronger was 0 for oil added and 14 for no addition (significant at the 1% level). Table 7 shows that the numbers of panelists who answered that the astringency with oil equaled that of solutions of 0.6, 0.55, 0.45 and 0.35 (× 10^-2 mol/L) were 0, 4, 7 and 3, with a weighted mean of 0.46 × 10^-2 mol/L. After taking 2.5 mL of edible oil into the mouth, all panelists felt the astringency of the caffeic acid solution as weaker.
Limitations: The solutions are models, not cooked eggplant. Components in the oil were not measured. Only astringency was evaluated, not bitterness. The statement that the astringency of eggplant is caused by the caffeic acid portion of chlorogenic acid is the authors' presumption. The number of comparison solutions differs within the paper: the preparation text and Table 7 give 4 concentrations, whereas the presentation text says '3 kinds'.
eggplant is processed by Soaking in water. Even when eggplant cut into 8 pieces was soaked 3 times for 5 minutes each in water (20°C) at 5 times its weight, only 3.1% (5.1 mg) of the total polyphenols (165.3 mg per 100 g of raw eggplant) and 1.1% (1.0 mg) of the chlorogenic acid (88.8 mg likewise) came out into the water, and most remained in the eggplant.preliminary
Scope: Commercially available eggplant (Sennari), cut lengthwise into 8 skin-on boat-shaped pieces. Components were measured only; no sensory test was conducted.
Note: The authors write that eggplant cooked in oil after soaking in water would be perceived as less astringent than eggplant cooked in oil without soaking, but this is an inference, and this paper has no sensory result. Read it as material that raises, from the side of the components, a question about the reasons given for soaking in water, namely preventing browning and removing astringency.
In Table 3, total polyphenols were 165.3 mg (100%) in raw eggplant, 5.1 mg (3.1%) in the soaking water and 160.2 mg (96.9%) in the soaked eggplant. Chlorogenic acid was 88.8 mg in raw eggplant, 1.0 mg (1.1%) in the soaking water and 87.8 mg (98.9%) in the soaked eggplant. The main text states that neither total polyphenols nor chlorogenic acid moved much into the water and most remained in the soaked eggplant.
Limitations: Components were measured only. There was no sensory test, and the effect on astringency is an inference. The results are for the condition of cutting into eighths (8 pieces) and may not apply to cuts with a larger surface area, such as thin slices. 1 type of eggplant.
eggplant is processed by Sautéing and deep-frying. When 100 g of eggplant was sautéed, 51.7% of the total polyphenols and 59.8% of the chlorogenic acid had moved into the oil adhering to the surface; when deep-fried, 37.3% of the total polyphenols and 47.7% of the chlorogenic acid had moved into the adhering oil. Only 0.7 mg of total polyphenols and 0.2 mg of chlorogenic acid had moved into the frying oil left in the pan.preliminary
Scope: Commercially available eggplant (Sennari) cut into eighths (8 pieces). A case sautéed for 4 minutes in 30 mL of salad oil and a case deep-fried for 3 minutes in 500 mL of salad oil at 170°C. Components were measured only; no sensory test was conducted.
Note: This measures the distribution of total polyphenols and chlorogenic acid, which the authors call "astringent components"; the sensory astringency was not measured. The components in the adhering oil are the amounts washed out with methanol. The reasons for the different transfer ratios in sautéing and deep-frying (heating time, oil uptake, tissue breakdown by stirring) are the authors' conjecture. Read it together with the 1986 sensory result (astringency was weaker when sautéing or deep-frying with oil).
Table 1 (sautéing, per 100 g of eggplant): total polyphenols were 240.8 mg (100) in the whole sautéed eggplant, 124.6 mg (51.7) in the adhering oil and 116.2 mg (48.3) in the eggplant without the oil. Chlorogenic acid was 121.0 in the whole, 72.4 (59.8) in the adhering oil and 48.6 (40.2) in the eggplant without the oil. Table 2 (deep-frying): total polyphenols were 315.4 mg in the whole, 117.8 (37.3) in the adhering oil and 197.6 (62.7) in the eggplant without the oil. Chlorogenic acid was 131.1 in the whole, 62.6 (47.7) in the adhering oil and 68.5 (52.3) in the eggplant without the oil. The oil left in the frying pan held 0.7 mg of total polyphenols and 0.2 mg of chlorogenic acid.
Limitations: There is no sensory test. Components were measured only, and whether transfer into the adhering oil weakens the perception of astringency is an inference from the 1986 model experiment. Heating time and oil uptake differ between sautéing and deep-frying.