Original papers
Comparative Aroma Extract Dilution Analysis of Changes in Aroma Components of Seasoned Soy Sauce Prepared from Soy Sauce and Mirin during Heating
2020 年 26 巻 6 号 p. 725-733
詳細
2020 年 26 巻 6 号 p. 725-733
An investigation using Aroma Extract Dilution Analysis (AEDA) applied to the aroma concentrate of a model heated seasoned soy sauce, prepared from soy sauce and mirin, revealed 36 aroma peaks, and 32 compounds were identified or tentatively identified from the detected peaks. Among them, 3-(methylthio) propanal was the most dominant compound, showing the highest Flavor Dilution (FD) factor, followed by 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone, and 3-hydroxy-4,5-dimethyl-2(5H)-furanone. While most of the identified compounds have already been reported, 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone was identified in the seasoned soy sauce for the first time. A comparative AEDA study of the unheated and heated seasoned soy sauces revealed that approximately half of the aroma peaks were detected at FD factors that were 16-fold higher in the heated seasoned soy sauce, while the remainder showed equal or highly similar FD factors. This indicated that the heating history of the seasoned soy sauce as well as the materials employed are important in the aroma of heated seasoned soy sauce, and a limited number of aroma components are related to changes in the seasoned soy sauce aroma by heating. Finally, relative quantitative analysis of aroma active compounds, i.e., Strecker aldehydes, furanone/pyranones, and phenols, in the seasoned soy sauce heated for different times revealed that only a few components greatly increased during heating and these might be important for the changes in the seasoned soy sauce aromas with different heating times.
Most Japanese cuisines, collectively called Washoku, are mainly seasoned with soy sauce, soy paste, Japanese rice wine, Japanese sweet rice wine (mirin), sugars, vinegars, salt as well as soup stocks extracted from dried-bonito, dried kelp, and/or shiitake mushroom (i). Especially, soy sauce and Japanese rice wine are essential seasonings for preparing such traditional Japanese cuisines as grilled dishes (Teriyaki, Kabayaki), simmered dishes (Nitsuke, Nimono), and many kinds of pan-fried dishes (PJ Group Publishing, 2014; Kenmizaki, 2011).
The key aroma compounds of the respective ingredients for Japanese cuisines have been reported before. The most important aroma components in Japanese soy sauce were Strecker aldehydes such as 3-methylbutanal and 3-(methylthio)propanal (methional), phenols such as 4-ethyl-2-methoxyphenol and 2-methoxy-4-vinylophenol, and furanones such as 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone (HEMF), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF), and 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon), which were clarified using Aroma Extract Dilution Analysis (AEDA) (Steinhaus and Schieberle, 2007; Kaneko et al., 2012). The key aroma components in mirin were recently identified using AEDA as methional, sotolon, 3-methylbutanoic acid, 2-methylbutanoic acid, and 2-methoxy-4-vinylphenol (Kaneko and Kumazawa, 2015).
On the other hand, there have been few investigations concerning the key aroma components in cooked Japanese traditional seasonings. Meng et al. (2015) investigated changes in a seasoning aroma following a short duration of high heat in a pan (280 °C, 10 sec) as a model sauce composed of soy sauce, mirin, and sugar. It was revealed that the number of aroma active components in the seasoned soy sauce increased after heating by Gas Chromatography-Olfactometry (GC-O) analysis, while those in the soy sauce decreased. This indicates that mirin and/or sugar imparts not only a sweet taste but also a complex aroma during the preparation. Additionally, the number of detectable aroma peaks in the seasoned soy sauce prepared from soy sauce and glucose was greater than that in the seasoned soy sauce prepared from soy sauce and sugar (sucrose). This indicates that mirin composed mainly of glucose and its dimers (maltose, isomaltose, kojibiose) is important in the aroma generation of seasoned soy sauce.
Recipes of traditional Japanese seasoned soy sauce using soy sauce, mirin, sugar, and/or Japanese rice wine differ according to the dish. For example, whereas pan-fried seasoned soy sauce is generally prepared quickly over high heat, Nitsuke (boiled fish) and Nimono (boiled vegetable and meat/fish) are prepared over a long period of time by gently heating in a pot.
Although the aroma active compounds in the respective seasonings of soy sauce and mirin have been reported previously, those in cooked seasoned soy sauce prepared from soy sauce and mirin have not yet been fully clarified. Therefore, the objectives of the present investigation were to elucidate the potent odorants in cooked seasoned soy sauce, prepared from soy sauce and mirin by simmer-type heating (gently heating in a pot for a long period of time to make Nitsuke or Nimono), and assess their changes according to differences in heating time.
Materials Soy sauce (Tokusen Marudaizu Shoyu, 500 mL PET bottle, JAN code: 4901515120404) (Kikkoman Co., Ltd., Noda, Japan) and mirin (Takara Jun-Mai Hon-mirin, 600 mL PET bottle, JAN code: 4904670110068) (Takara Shuzo Co., Ltd., Kyoto, Japan) were purchased at a supermarket.
Chemicals 2,6-Dimethoxy-4-vinylphenol, 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone (dihydromaltol), trans-4,5-epoxy-(E)-2-decenal, and 2,3-dihydro-3,5-dihydroxy-6-methyl-4(4H)-pyranone (hydroxymaltol) were synthesized according to the literature (Kaneko et al., 2013; Mills, 1972; Kumazawa et al., 2006; Kim and Baltes, 1996). Compounds (Table 1) 1a, 1b, 2, 3, 4, 5, 6, 7, 8, 9, 11a, 11b, 12, 15, 16, 18, 20, 22, 23, 25, 27, 30, 34, and 36 were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Compounds 28, 29, and 33 were purchased from Sigma-Aldrich Japan Co., Ltd. (Tokyo, Japan). Sucrose was purchased from Kanto Chemical Co., Inc. (Tokyo, Japan).
| No. | RI | odor qualities | compoundb | FD factorcde | |||
|---|---|---|---|---|---|---|---|
| heated | unheated | soy sauce | mirin | ||||
| 1a/1b | 954 | malty | 2-methylbutanal/3-methylbutanal | 16 | 1 | 1 | nd |
| 2 | 977 | milky | 2,3-butanedione | 16 | 16 | 16 | nd |
| 3 | 1409 | sour | acetic acid | 64 | 64 | 64 | nd |
| 4 | 1425 | pea-like, earthy | 2-isopropyl-3-methoxypyrazinef | 16 | 16 | 16 | 1 |
| 5 | 1449 | cooked potato-like | 3-(methylthio)propanal (methional) | 16384 | 1024 | 1024 | 1024 |
| 6 | 1458 | nutty, earthy | 2-ethyl-3,5-dimethylpyrazine | 16 | 4 | 4 | 4 |
| 7 | 1617 | sour | butanoic acid | 16 | 4 | 4 | 4 |
| 8 | 1625 | cereal-like | 2-acetylthiazoleg | 16 | nd | nd | nd |
| 9 | 1639 | honey-like | phenylacetaldehyde | 64 | 1 | 1 | nd |
| 10 | 1657 | roasty | unknown | 16 | nd | nd | nd |
| 11a/11b | 1663 | sour | 2- or 3-methylbutanoic acid | 256 | 256 | 256 | 64 |
| 12 | 1715 | cooked potato-like | 3-(methylthio)propanol (methionol) | 16 | 64 | 64 | nd |
| 13 | 1727 | caramel-like | unknown | 64 | 4 | 4 | 4 |
| 14 | 1804 | cereal-like | unknown | 16 | nd | nd | nd |
| 15 | 1836 | seasoning-like | 2-hydroxy-3-methyl-2-cyclopentan-1-one | 16 | 16 | 16 | nd |
| 16 | 1853 | spicy, anis-like | 2-methoxyphenol | 256 | 256 | 256 | 4 |
| 17 | 1858 | caramel-like | 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone (dihydromaltol)g | 256 | 4 | 4 | nd |
| 18 | 1882 | almond-like, floral | ethyl 3-phenylpropanoateg | 16 | 4 | 4 | nd |
| 19 | 1892 | floral, sweet | unknown | 16 | nd | nd | nd |
| 20 | 1970 | caramel-like | 3-hydroxy-2-methyl-4(4H)-pyranone (maltol) | 64 | 16 | 16 | nd |
| 21 | 2003 | metallic | trans-4,5-epoxy-(E)-2-decenalf | 16 | nd | nd | nd |
| 22 | 2024 | burnt, plastic-like | 4-ethyl-2-methoxyphenol | 64 | 256 | 256 | nd |
| 23 | 2030 | caramel-like | 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) | 4096 | 1024 | 1024 | 1 |
| 24 | 2051 | spicy | 3-hydroxy-6-methyl-2(2H)-pyranonegh | 16 | nd | nd | nd |
| 25 | 2061 | caramel-like | 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone (HEMF) | 4096 | 4096 | 4096 | nd |
| 26 | 2085 | sulfurous | unknown | 16 | nd | nd | nd |
| 27 | 2131 | cinnamon-like | ethyl cinnamatef | 16 | 16 | 16 | 4 |
| 28 | 2191 | spicy | 2-methoxy-4-vinylphenol | 1024 | 64 | 64 | 64 |
| 29 | 2194 | seasoning-like | 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon) | 4096 | 4096 | 1024 | 256 |
| 30 | 2260 | spicy | 2,6-dimethoxyphenol | 256 | 256 | 256 | nd |
| 31 | 2278 | caramel-like, seasoning-like | 2,3-dihydro-3,5-dihydroxy-6-methyl-4(4H)-pyranone (hydroxymaltol) | 64 | 1 | 1 | nd |
| 32 | 2375 | floral, grape-like | unknown | 64 | nd | nd | nd |
| 33 | 2549 | honey-like | phenylacetic acid | 64 | 64 | 64 | 4 |
| 34 | 2558 | vanilla-like | 4-hydroxy-3-methoxybenzaldehyde (vanillin) | 256 | 64 | 64 | 64 |
| 35 | 2566 | spicy, burnt | 2,6-dimethoxy-4-vinylphenol | 64 | 1 | 1 | nd |
| 36 | 2617 | cinnamon-like | 3-phenylpropanoic acid | 64 | 1 | 1 | nd |
Preparation of Seasoned Soy Sauce from Soy Sauce and Mirin The mixture of 5 mL of soy sauce, 7.5 mL of mirin, 3 g of sucrose, and 7.5 mL of distilled water was added to a 200-mL three-necked flask connected to a Dimroth condenser. The flask was settled into the mantle heater (Taika Denki Co., Ltd., Osaka, Japan) connected to a variable transformer (Tokyo-Rikosha Co., Ltd., Saitama, Japan) regulated at 80 V. The condenser coolant was set as 5 °C. The seasoned soy sauce was boiled for 5 min, and then maintained at boiling in the flask. The seasoned soy sauces were prepared with different heating times of 0, 5, 11, 17, and 29 min in this study.
Preparation of Soy Sauce and Mirin Samples for Comparative AEDA of Seasoned Soy Sauce For comparative AEDA of the seasoned soy sauce prepared from soy sauce and mirin, the soy sauce sample was prepared by mixing 5 mL of soy sauce and 15 mL of distilled water, and the mirin sample was prepared by mixing 7.5 mL of mirin and 12.5 mL of distilled water; thus, the respective omitted materials were replaced with distilled water.
Preparation of Aroma Concentrates of Soy Sauce, Mirin, and Seasoned Soy Sauce for GC-MS and GC-O Analyses After adding 80 mL of distilled water and 2-octanol (500 µg/L) as an internal standard to 20 mL of the soy sauce sample, mirin sample, or seasoned soy sauce, the obtained mixture was extracted three times with 100 mL of dichloromethane. After drying with an excess amount of anhydrous sodium sulfate, the dichloromethane extract was distilled by solvent-assisted flavor evaporation (SAFE) at 40 °C under <5.0 × 10−3 Pa (Engel et al., 1999). The aroma concentrates were obtained from the distillates by rotary evaporation and subsequent nitrogen steam concentration to about 100 µL. The respective aroma concentrates were applied to GC-O analysis for the AEDA study and Gas Chromatography-Mass Spectrometry (GC-MS) for identification and quantitative analyses.
Identification of Aroma Active Compounds in the Aroma Concentrate To identify minute amounts of aroma active components, a scale-up experiment was conducted. The mixture of 100 mL of soy sauce, 150 mL of mirin, 60 g of sucrose, and 150 mL of distilled water was added to a 2 000-mL round flask. The flask was settled into the mantle heater connected to a variable transformer regulated at 100 V; the condenser coolant was set to 5 °C and 1.0 L/min of dried air flowed through the flask. The seasoned soy sauce was boiled at 10 min, and then maintained at boiling in the system for another 10 min. The obtained seasoned soy sauce was extracted three times with 200 mL of dichloromethane. After drying with an excess amount of anhydrous sodium sulfate, the dichloromethane extract was distilled by SAFE at 40 °C under <5.0 × 10−3 Pa. The aroma concentrate of the seasoned soy sauce was obtained from the distillate by rotary evaporation and subsequent nitrogen steam concentration to about 100 µL. Identification of each aroma compound was performed by comparing its Kovats GC retention index (RI) and mass spectrum with the authentic compound by GC-MS using a DB-Wax column. In addition, the RI and odor quality was compared to the authentic compound by GC-O analysis using the DB-Wax column.
GC-O An Agilent model 6850 series gas chromatograph (Agilent Technologies, Santa Clara, CA) equipped with a thermal conductivity detector (TCD) was used for the GC-O analysis. A fused silica column (30 m × 0.25 mm i.d. coated with a 0.25 µm film of DB-Wax, J&W Scientific, Folsom, CA; or 30 m × 0.25 mm i.d. coated with a 0.25 µm film of DB-1, J&W Scientific) was used with 1.0 µL splitless injection. Helium was used as the carrier gas at a flow rate of 1 mL/min. The injector temperature was set to 250 °C and the purge valve was opened at 60 sec. The chromatography was performed at an oven temperature of 40 °C, which was increased to 210 °C at a rate of 5 °C/min. The detector temperature was set to 230 °C. A glass sniffing port was connected to the outlet of the TCD and heated to >210 °C by a ribbon heater. Moist air was pumped into the sniffing port at 100 mL/min to quickly remove the odorant eluted from the TCD out of the sniffing port. The aroma concentrates underwent a GC-O analysis by three subjects. Determination of the odor qualities detected by sniffing was achieved by triplicate experiments for each subject. The subjects were trained according to the previous study (Kaneko et al., 2012).
AEDA The original aroma concentrate was stepwise diluted with dichloromethane from 1:4 to 1:65536, and then aliquots (1 µL) of each fraction were analyzed by capillary GC on a DB-Wax column. AEDA was performed three times with respect to each sample by three subjects (Schieberle, 1995). The detection of each compound was defined as not less than two detections by all subjects, and the FD factor of each compound was determined as the maximum dilution degree of detection.
GC-MS An Agilent 7890A gas chromatograph coupled to an Agilent model 5975C inert XL series mass spectrometer was used. A fused silica column (60 m × 0.25 mm i.d. coated with a 0.25 µm film of DB-Wax, J&W Scientific; or 60 m × 0.25 mm i.d. coated with a 0.25 µm film of DB-1, J&W Scientific) was used for the analyses. Helium was used as the carrier gas at a flow rate of 1 mL/min, and the injector temperature was set to 250 °C. Aliquots (1 µL) of the sample were injected at a split ratio of 1:30 or in splitless mode. The chromatography was performed from an oven temperature of 80 °C to 210 °C at a rate of 3 °C/min for the split injections, and from an oven temperature of 40 °C to 210 °C at a rate of 3 °C/min for the splitless injections. The mass spectrometer was used under the following conditions: ionization voltage of 70 eV (EI) and ion source temperature of 150 °C.
Identification of Aroma Active Compounds in the Aroma Concentrate of Heated Seasoned Soy Sauce Prepared from Soy Sauce and Mirin To identify aroma active compounds in the aroma concentrate of the seasoned soy sauce prepared from soy sauce and mirin, AEDA was applied to the aroma concentrate of the seasoned soy sauce heated for 11 min as a model sauce. Thirty-six aroma peaks were detected by GC-O as having a FD factor of ≥16, and 32 compounds were identified or tentatively identified from the detected peaks (Table 1). Among them, methional (5) was identified as having the highest FD factor of 16384, followed by HDMF (23), HEMF (25), and sotolon (29) with the next highest FD factor of 4096. 3-Methylbutanoic acid (11a), 2-methylbutanoic acid (11b), 2-methoxyphenol (16), 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone (dihydromaltol) (17), 2-methoxy-4-vinylphenol (28), 2,6-dimethoxyphenol (30), and 4-hydroxy-3-methoxybenzaldehyde (vanillin) (34) were detected with moderate FD factors of 256-1024. As in the previous paper by Meng et al., (2015), HDMF (23), HEMF (25), sotolon (29), and 2-methoxyphenol (16) were detected with high FD factors in the aroma concentrate of the soy sauce preparation.
The majority of compounds were previously identified as aroma active compounds of soy sauce, mirin, or seasoned soy sauce prepared from soy sauce and mirin (Steinhaus and Schieberle, 2007; Kaneko et al., 2012; Kaneko and Kumazawa, 2015; Meng et al., 2015); however, 2-acetylthiazole (8), 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone (dihydromaltol) (17), ethyl 3-phenylpropanoate (18), and 3-hydroxy-6-methyl-2(2H)-pyranone (24) were identified or tentatively identified from the seasoned soy sauce for the first time. Especially, dihydromaltol (17) is a noteworthy component, since it had a relatively high FD factor of 256 in the aroma concentrate. As reported by Preininger et al. (2009), dihydromaltol (17) has a quite low odor detection threshold (50–250 µg/kg in water) compared to the dehydro-form of maltol (7 100–13 000 µg/kg in water). In light of this report and the relatively high FD factor of dihydromaltol (17) in the aroma concentrate, it might be one of the important odorants in heated seasoned soy sauce prepared from soy sauce and mirin.
Comparative AEDA of Aroma Active Compounds in the Aroma Concentrates of Heated/Unheated Seasoned Soy Sauce Prepared from Soy Sauce and Mirin, Soy Sauce, and Mirin To clarify the origin of the aroma active compounds detected in the aroma concentrate of the heated seasoned soy sauce prepared from soy sauce and mirin, a comparison was made to the unheated seasoned soy sauce, soy sauce, and mirin (Table 1). Comparative AEDA of the unheated and heated seasoned soy sauces revealed that approximately half of the aroma peaks (17 of 36 aroma peaks) were detected with FD factors 16-fold higher in the heated seasoned soy sauce, while the remaining 19 aroma peaks were detected with equal or similar FD factors. This indicated that the heating history of the seasoning as well as the materials employed are important for the aroma of the heated seasoned soy sauce, and a limited number of aroma components appear to be related to the changes in seasoned soy sauce aroma by heating.
Only 4-ethylphenol was greatly decreased during heating (FD-factor of 1) compared to the unheated seasoned soy sauce with a FD factor of 16 (data not shown). Almost all of the aroma active compounds were common between the aroma concentrates of the unheated seasoned soy sauce and the soy sauce, whereas few volatiles were common between those of the mirin and the unheated seasoned soy sauce (5, 11a, 11b, 28, 29, 34). The unchanged aroma active compounds during heating in the seasoned soy sauce were, therefore, mainly derived from the soy sauce.
On the other hand, volatile components increased by heating were Strecker aldehydes (1a, 1b, 5, 9), pyranones/furanones (17, 20, 23, 31), and phenols (16, 28, 30, 35), which are thought to be generated by the Maillard reaction or a decarboxylation reaction from phenolic acids. In a previous study, Strecker aldehydes, phenols, and some furanones were increased by the heating of soy sauce (Kaneko et al., 2013). Meng et al. (2015) reported that some furanones (23, 4-hydroxy-5-methyl-3(2H)-furanone) were greatly increased by high heat for a short period of time (280 °C, 10 sec). In the present study, some of the other pyranone derivatives (17, 24, 31) were, however, uniquely detected in the seasoned soy sauce prepared from soy sauce and mirin by gently heating for a long duration. Meng et al. (2015) reported that a larger number of aroma peaks exhibiting a sweet aroma note were detected in the seasoned soy sauce prepared from soy sauce with mirin or glucose by GC-O, and a small number of sweet aroma peaks were detected in soy sauce with/without sugar. They concluded that glucose or mirin, which contains a high concentration (30–40%) of mono- and di-saccharides of glucose, maltose, isomaltose, and kojibiose, were essential in imparting the typical sweet aroma to the heated soy sauce product used in Japanese traditional cuisine.
Relative Quantitative Analysis of Aroma Compounds in Heated and Unheated Soy Sauce Preparations Relative quantitative analysis was conducted to more precisely understand changes during heating, by focusing on aroma components with high FD factors (Table 2). It was revealed that only 7 out of 20 compounds were greatly increased with heating. Among the greatly increased compounds, Strecker aldehydes (5, 9) were greatly increased by heating (20.7, 19.8 times, respectively), which was also reported by Kaneko et al. (2013) in soy sauce alone. Moreover, certain pyranones (17, 31) were greatly increased during heating only in the case of the seasoned soy sauce (27.6, 35.4 times, respectively). This might be because mirin is rich in glucose and its dimers, which are the sources of the above two compounds produced through the Maillard reaction or by heat deterioration. Furthermore, some phenols (28, 35) were greatly increased after heating (20.6, 50.8 times, respectively). As reported earlier, whereas vinylphenols can easily decompose with heating due to reactivity of the precursors of hydroxycinnamic acid derivatives, phenols (16, 30) derived from hydroxybenzoic acid derivatives did not greatly increase (1.06, 1.27 times, respectively) (Kaneko et al., 2013). Meanwhile, HEMF (25) and sotolon (29), which exhibited the second highest FD factor of 4096 in the heated seasoned soy sauce, did not change after heating. It was reported that HEMF (25) is generated in fermented soy products by the Maillard reaction and reacts with yeast metabolites (Sugawara, 2001); thus, HEMF (25) did not increase during heating in the seasoned soy sauce. There are several formation mechanisms for sotolon (29) in natural sources and it has been reported that sotolon (29) was generated in cane molasses by heating (Kobayashi, 1989). However, the application of low heat in the present experiment might not cause increases in sotolon (29) by this reaction. On the other hand, whereas differences could not be observed by comparative AEDA study, some aroma compounds (3, 11a, 11b, 12, 22, 25, 33) were slightly decreased after heating. Notably, acids (3, 11a, 11b, 33) were decreased, as they might vaporize during heating or decompose by a decarboxylation reaction similar to that in the formation mechanism of phenols, namely by a decarboxylation reaction from the respective corresponding carboxylic acids. On the contrary, 3-phenylpropanoic acid (36) was significantly increased after heating. The formation mechanism is still unclear and requires further investigation.
| No. | compounda | concentration,bc µg/kg (SD,d µg/kg) | ratio | |
|---|---|---|---|---|
| unheated | heated | |||
| 3 | acetic acid | 4270 (± 220) | 1320 (± 40) | 0.309 |
| 5 | 3-(methylthio)propanal (methional) | 19.0 (± 1.4) | 393 (± 29) | 20.7 |
| 9 | phenylacetaldehyde | 68.8 (± 10.2) | 1360 (± 120) | 19.8 |
| 11a | 3-methylbutanoic acid | 149 (± 6) | 100 (± 8) | 0.671 |
| 11b | 2-methylbutanoic acid | 61.4 (± 4.7) | 34.8 (± 2.6) | 0.567 |
| 12 | 3-(methylthio)propanol (methionol) | 564 (± 24) | 289 (± 54) | 0.512 |
| 13 | unknown | - | - | - |
| 16 | 2-methoxyphenol | 12.5 (± 1.1) | 13.3 (± 0.3) | 1.06 |
| 17 | 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone (dihydromaltol) | 5.69 (± 0.42) | 157 (± 13) | 27.6 |
| 20 | 3-hydroxy-2-methyl-4(4H)-pyranone (maltol) | 823 (± 72) | 887 (± 27) | 1.08 |
| 22 | 4-ethyl-2-methoxyphenol | 20.3 (± 1.2) | 15.1 (± 0.8) | 0.744 |
| 23 | 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) | 140 (± 6) | 435 (± 31) | 3.11 |
| 25 | 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone (HEMF) | 5540 (± 200) | 5020 (± 260) | 0.906 |
| 28 | 2-methoxy-4-vinylphenol | 22.0 (± 3.7) | 454 (± 17) | 20.6 |
| 29 | 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon) | 27.9 (± 2.1) | 25.2 (± 2.7) | 0.903 |
| 30 | 2,6-dimethoxyphenol | 38.8 (± 0.6) | 49.2 (± 2.8) | 1.27 |
| 31 | 2,3-dihydro-3,5-dihydroxy-6-methyl-4(4H)-pyranone (hydroxymaltol) | 123 (± 18) | 4360 (± 860) | 35.4 |
| 32 | unknown | - | - | - |
| 33 | phenylacetic acid | 468 (± 46) | 269 (± 56) | 0.575 |
| 34 | 4-hydroxy-3-methoxybenzaldehyde (vanillin) | 26.2 (± 1.0) | 39.0 (± 2.5) | 1.49 |
| 35 | 2,6-dimethoxy-4-vinylphenol | 2.58 (± 0.10) | 131 (± 6) | 50.8 |
| 36 | 3-phenylpropanoic acid | 2.15 (± 0.23) | 42.5 (± 5.0) | 19.8 |
In summary, following relative quantitative analysis, the aroma active compounds screened by AEDA were classified into 3 types (greatly increased, unchanged, and reduced). Especially, methional (5), phenylacetaldehyde (9), dihydromaltol (17), 2-methoxy-4-vinylphenol (28), hydroxymaltol (31), 2,6-dimethoxy-4-vinylphenol (35), and 3-phenylpropanoic acid (36) were greatly increased after heating, indicating their importance in the characteristic heated aroma of the seasoned soy sauce prepared from soy sauce and mirin.
Successive Changes in Aroma Compounds of the Seasoned Soy Sauce Prepared from Soy Sauce and Mirin during Heating Because seasoned soy sauce recipes differ by cooking method, the composition of the seasonings of the soy sauce, mirin, sugar, and Japanese rice wine varies in addition to the heating condition. To more precisely clarify the relationship between heating history and key aroma compounds in the model seasoned soy sauce prepared from soy sauce and mirin, relative quantitative analysis of Strecker aldehydes, pyranones, furanones, and phenols, which were detected by AEDA analysis of the aroma concentrate of the seasoned soy sauce, was applied to the unheated and heated seasoned soy sauces with different heating times. Strecker aldehydes successively increased during heating (Fig. 1); however, two different behaviors were observed among them. The aldehydes either continuously increased (Fig. 1C, 1D), or increased by heating and then plateaued (Fig. 1A, 1B). Although we were unable to precisely explain these results from the data, this difference might be attributed to changes in the equilibrium of the formation rate and the decomposition rate during heating.
Changes of Strecker aldehydes in seasoned soy sauce during heating. 2-methylbutanal (A); 3-methylbutanal (B); 3-(methylthio)propanal (C); phenylacetaldehyde (D)
Pyranones and furanones were separated into 2 different behaviors (Fig. 2). Whereas dihydromaltol (17), hydroxymaltol (31), maltol (20), and HDMF (23) were significantly increased during heating (Fig. 2A, 2B, 2C, 2F), increases in HEMF (25) and sotolon (29) were not observed (Fig. 2D, 2E). On the other hand, considering the AEDA study of heated and unheated seasoned soy sauces, maltol (20) and HDMF (23) did not appear to be important in the differences of heated aroma, since these were present even in the unheated seasoned soy sauce (823 µg/L and 140 µg/L, respectively (Table 2)). This is in agreement with the slight increase in the FD factor of these compounds (16→64, 1024→4096, respectively). Further, it can be concluded that dihydromaltol (17) and hydroxymaltol (31) might contribute to changes in the aroma profile during heating, but HEMF (25) and sotolon (29) as well as maltol (20) and HDMF (23) might not be so important.
Changes of furanones/pyranones in seasoned soy sauce during heating. 2,3-dihydro-5-hydroxy-6-methyl-4(4H)-pyranone (A); 3-hydroxy-2-methyl-4(4H)-pyranone (B); 4-hydroxy-2,5-dimethyl-3(2H)-furanone (C); 5(or 2)-ethyl4-hydroxy-2(or 5)-methyl-3(2H)-furanone (D); 3-hydroxy-4,5-dimethyl-2(5H)-furanone (E); 2,3-dihydro-3,5-dihydroxy-6-methyl-4(4H)-pyranone (F)
Whereas 2-methoxy-4-vinylphenol (28) and 2,6-dimethoxy-4-vinylphenol (37) greatly increased during heating, 2-methoxyphenol (16) and 2,6-dimethoxyphenol (30) slightly increased and 4-ethyl-2-methoxyphenol (22) slightly decreased during heating (Fig. 3). This is in good agreement with the previous model study, which was strongly affected by the reactivity of the decarboxylation reaction of the respective phenolic acids (Kaneko et al., 2013).
Changes of phenols in seasoned soy sauce during heating. 2-methoxyphenol (A); 4-ethyl-2-methoxyphenol (B); 2-methoxy-4-vinylphenol (C); 2,6-dimethoxyphenol (D); 2,6-dimethoxy-4-vinylphenol (E)
Whereas Meng et al. (2015) reported that only 4 compounds were slightly increased in the model pan-fried seasoned soy sauce, most of the key aroma components having a FD factor ≥64 showed significant changes in the model boiled seasoned soy sauce in this investigation (Table 2). This might be because the long duration (11 min) of heating had a large influence, even though the heating temperature was low (boiling) compared with the report by Meng et al. (280 °C, 10 s).
In conclusion, a limited number of components in the aroma concentrates of seasoned soy sauces (e.g., Teriyaki sauce, Nitsuke, and Nimono) were related to the differences in potent odorants screened by AEDA during heating. Notably, Strecker aldehydes (methional, phenylacetaldehyde), pyranones (dihydromaltol, hydroxymaltol), and phenols (vinylphenols) greatly increased during heating and might be important mediators of the changes in seasoned soy sauce aromas identified by AEDA. Whereas many compounds were identified by the AEDA study, some of the aroma peaks remain unknown. Further investigation is expected to generate additional knowledge of the aroma profiles of seasoned soy sauces.
