Abstract
Recent studies have shown that γ-glutamyl peptides (GGPs) are recognized by the calcium-sensing receptor and induce kokumi taste. The contents of GGP have been reported in some fermented foods such as cheese and Japanese soy sauce but not in ganjang and doenjang which are representative Korean fermented-soybean products. In this study, the qualitative and quantitative analyses of GGPs in several ganjang and doenjang were carried out by LC-MS/MS using 11 synthetic GGPs as reference compounds. The total GGP contents ranged from 92 to 620 μg/mL for ganjang and from 203 to 387 μg/g for doenjang, respectively. Interestingly, the levels of GGPs were not related to manufacturing types of traditional and industrial products. These data provide a basis for the taste of ganjang and doenjang which was expressed abstractly as mouthful and long-lasting taste.
Supplementary Information
The online version contains supplementary material available at 10.1007/s10068-021-00993-x.
Keywords: γ-glutamyl peptide, Kokumi taste, LC-MS/MS (MRM mode), Ganjang, Doenjang
Introduction
Ganjang (Korean soy sauce) and doenjang (Korean fermented-soybean paste) are the representative fermented-soybean products in Korea (Shin and Jeong, 2015). They have been used favorably as natural condiments by consumers. Ganjang is usually used to impart salty and savory taste to foods. Several ingredients such as amino acids, peptides, saccharides, and organic acids contribute to the taste of ganjang (Lee et al., 2002; Shin and Jeong, 2015). Doenjang has a unique taste and flavor, which are very different from those of ganjang (Lee et al., 2018). The tastes of ganjang and doenjang are often described very abstractly as ‘gusuhada’ in Korean, which means mouthful and long-lasting taste.
The sixth taste called ‘kokumi’ was first introduced in 1990 (Ueda et al., 1990, 1997). Kokumi taste is described as mouthful, thick, and long-lasting taste (Ueda et al., 1990), which is very similar to the description of the unique taste of ganjang and doenjang. Kokumi taste is induced by γ-glutamyl peptides (GGPs) and sulfur-containing compounds which are perceived through the calcium-sensing receptor (CaSR) (Maruyama et al., 2012; Ohsu et al., 2010). The presence of GGPs has been confirmed in various foodstuffs including edible legumes, Alliaceae, and fermented foods such as cheeses, soy sauce, fermented fish, and yeast extract (Yang et al., 2019). Especially, GGPs are responsible for the kokumi taste of some kinds of cheese (Hillmann et al., 2016; Roudot-Algaron et al., 1994; Toelstede et al., 2009; Toelstede and Hofmann, 2009). Some GGPs were also identified in Japanese soy sauce, however, only five kinds of GGPs have been reported (Frerot and Chen, 2013; Kuroda et al., 2013).
Ganjang and doenjang are expected to contain GGPs given their kokumi taste and the involvement of several microorganisms which can produce GGPs in proteinous substrates. Traditionally, ganjang and doenjang are made from meju, which is a brick of boiled soybeans fermented by the natural inoculation of a diverse group of microorganisms. Traditional meju contains different molds depending on the types and the regions. Despite kokumi-like taste of ganjang and doenjang, to the best of our knowledge, the qualitative and quantitative analyses of their GGPs have not been reported.
In this study, we analyzed the profile of GGPs in ganjang and doenjang to understand their unique taste which cannot be explained by previously reported taste and flavor ingredients. Therefore, our study will provide the scientific basis for the abstractive description of the taste of ganjang and doenjang.
Material and methods
Chemicals and ganjang and doenjang samples
Reference compounds of GGPs (γ-Glu-Glu, γ-Glu-Gly, γ-Glu-Gln, γ-Glu-Met, γ-Glu-Leu, γ-Glu-His, γ-Glu-Phe, γ-Glu-Trp, γ-Glu-Tyr, γ-Glu-Val, γ-Glu-Val-Gly) were purchased from Bachem (Weil am Rhein, Germany). γ-Glutamyl-valyl-glycine was chemically synthesized, as previously reported (Ohsu et al., 2010). The stable isotope of 15 N-uniformly labelled l-Arg (Arg-UN) purchased from Sigma Aldrich (Tokyo, Japan) was used as internal standard (ISTD). LC-MS grade acetonitrile (Junsei Chemicals Co., Ltd., Osaka, Japan), ammonium acetate (99%, Wako Pure Chemical Industries Ltd., Osaka, Japan) and water (Fisher Scientific, Hampton, VA, USA) were used to make the mobile phase.
A total of 12 samples for ganjang and 9 samples for doenjang were purchased from Korean markets in 2018. Ganjang samples were grouped into three types: traditional ganjang, industrial brewed ganjang, and industrial mixed ganjang that are made by mixing industrial brewed ganjang and acid-digested ganjang. Doenjang samples were grouped into traditional and industrial doenjang.
Ganjang and doenjang sample preparation for LC-MS/MS
A ganjang sample was directly diluted 50 times with deionized water containing the final concentration of 1 ppm ISTD. The water-soluble extracts (WSE) of a doenjang sample were prepared according to a protocol reported recently (Desfontaine et al., 2018). Briefly, a doenjang sample (10 g) was mixed with 40 mL of deionized water and homogenized for 5 min using a homogenizer in a Falcon tube. The homogenized sample was centrifuged at 10,062xg for 20 min at 4 °C. The upper layer and the precipitate were removed and the aqueous layer containing the doenjang WSE was transferred to a new tube. After re-extraction of the pellet with 40 mL of deionized water, the aqueous layers were combined with the first extract. The combined extracts were centrifuged at 10,062xg for 20 min at 4 °C, and the supernatants were filtered using a Whatman No. 1 filter paper (GE Healthcare, Chalfont St. Giles, UK). The filtered extract was freeze-dried and resuspended in deionized water. The WSE of a doenjang sample was stored at − 20 °C until further analysis.
Like a ganjang sample, the WSE of a doenjang sample were directly diluted 50 times with deionized water including ISTD prior to LC/MS. The diluted samples were filtered through a 0.45 μm syringe filter (25 mm GD/X disposable filter device, Whatman Corporation, Maidstone, UK) to remove the insoluble materials before analysis by LC/MS.
Standard GGPs, ganjang, and doenjang samples were derivatized using an AccQ Fluor reagent kit (Waters Corporation, Milford, MA, USA) following the protocol provided by Waters. Briefly, each sample (40 μL) was mixed with 60 μL of AQC reagent, 120 μL of borate buffer, 20 μL of 0.1 mg/dL ISTD, and 160 μL of 0.1% formic acid.
Analysis of GGPs by LC-MS/MS
GGPs were analyzed using a LC-MS/MS system at the Western Seoul Center of Korea Basic Science Institute (Seoul, Korea). Separation of GGPs were carried out by reversed-phase high-performance liquid chromatography using an Agilent 1290 Infinity II UHPLC system (Agilent Technologies, Palo Alto, CA, USA), equipped with a Waters BEH Amide column (1.7 μm, 2.1 × 75 mm; Waters, Corporation, Milford, MA, USA). The column temperature was maintained at 30 °C. Mobile phase A (MP A) consisted of aqueous 20 mM ammonium acetate in distilled water (D.W.) and mobile phase B (MP B) consisted of 20 mM ammonium acetate in 90% ACN and 10% D.W. The elution conditions were 0–4 min (95% MP B), 4–10 min (85% MP B), 10–12 min (50% MP B), and 12–15 min (95% MP B). The flow rate was set to 0.30 mL/min. Injection volume was 2 μL.
A 6495 Triple Quad MS system (Agilent Technologies) was used for detection. The Agilent Jet Stream Electrospray ion source was operated in positive mode at 3.5 kV. Peak detection of GGPs and ISTD were conducted using the MRM (multiple reaction monitoring) method. The following GGPs were analyzed using mass transitions given in parentheses: γ-Glu-Val-Gly (m/z 304 → 175), γ-Glu-Glu (m/z 277 → 148), γ-Glu-Met (m/z 279 → 150), γ-Glu-His (m/z 285 → 156), γ-Glu-Gln (m/z 276 → 147), γ-Glu-Gly (m/z 205 → 142), γ-Glu-Leu (m/z 261 → 132), γ-Glu-Val (m/z 247 → 118), γ-Glu-Tyr (m/z 311 → 182), γ-Glu-Trp (m/z 334 → 205), γ-Glu-Phe (m/z 295 → 166), respectively. ISTD (m/z 117 → 116) was monitored under the condition of the MRM transition channel. The collision energy was 15 V for each GGP and ISTD.
Quantitative analysis was performed in triplicate by comparing the peak areas obtained for the corresponding mass traces with those of defined standard solutions of each reference peptide ranging from 0.01 to 10 ppm (6-point calibration).
Results and discussion
Ganjang and doenjang samples were analyzed by LC-MS/MS with the MRM transition of each GGP. The identity of GGP peak was confirmed by spike test given that multiple peaks were measured in samples (Supplementary Fig. 1).
Contents of GGPs in ganjang
GGPs were present in all analyzed ganjang samples. The contents of total GGPs ranged from 76.53 to 445.61 mg/mL in traditional ganjang samples, from 84.58 to 620.88 mg/mL in industrial brewed ganjang samples, and from 20.20 to 153.31 mg/mL in industrial mixed ganjang samples (Table 1). These results indicate that GGPs are commonly contained in ganjang. The contents of γ-Glu-Val-Gly, the strongest tripeptide of kokumi taste, were determined to be below 5.38 mg/mL in ganjang samples whereas the tripeptide was found from 15 to 61 mg/mL in Japanese soy sauce (Kuroda et al., 2013). On the other hand, Ferrot and Chen (2013) reported that GGPs in the acidic fraction of soy sauce were analyzed to be 70 mg/kg (Frerot and Chen, 2013). These data suggest that the GGP contents vary among soy sauces.
Table 1.
Contents of GGPs in selected soy sauce samples (μg/mL)
| GGP | Traditional soy sauce | Industrial brewed soy sauce | Industrial mixed soy sauce | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| KM | JM | SM | HM | S701Y | S501Y | SY | MY | CY | SF3B | HB | NB | |
| γ-Glu-Trp | 0.09 ± 0.00 | 1.38 ± 0.00 | LOD* | 0.55 ± 0.00 | 0.85 ± 0.00 | 0.66 ± 0.00 | 0.76 ± 0.00 | 0.18 ± 0.00) | LOD* | 0.39 ± 0.00 | 0.66 ± 0.00 | LOD* |
| γ-Glu-Phe | 11.24 ± 0.19 | 13.45 ± 0.79 | 11.52 ± 0.22 | 71.10 ± 1.27 | 81.99 ± 2.48 | 48.21 ± 0.92 | 38.76 ± 0.88 | 10.92 ± 0.20 | 16.28 ± 0.33 | 19.97 ± 0.57 | 12.22 ± 0.06 | 1.26 ± 0.13 |
| γ-Glu-Leu | 9.59 ± 0.08 | 24.08 ± 0.58 | 15.78 ± 0.41 | 78.83 ± 1.73 | 77.60 ± 2.79 | 42.49 ± 0.94 | 34.95 ± 1.07 | 3.48 ± 0.14 | 3.34 ± 0.07 | 17.06 ± 0.65 | 6.01 ± 0.03 | 0.10 ± 0.06 |
| γ-Glu-Met | 2.60 ± 0.05 | 3.09 ± 0.15 | 2.38 ± 0.08 | 7.26 ± 0.19 | 37.99 ± 1.39 | 23.56 ± 0.46 | 21.69 ± 0.21 | 5.12 ± 0.14 | LOD* | 8.15 ± 0.19 | 3.92 ± 0.05 | 1.19 ± 0.02 |
| γ-Glu-Tyr | 1.70 ± 0.09 | 2.41 ± 0.18 | 1.93 ± 0.11 | 18.74 ± 0.68 | 11.52 ± 0.42 | 11.05 ± 0.44 | 17.00 ± 0.30 | 17.69 ± 0.32 | 20.63 ± 0.19 | 4.17 ± 0.21 | 10.55 ± 0.00 | 1.48 ± 0.11 |
| γ-Glu-Val | 5.53 ± 0.51 | 9.80 ± 0.64 | 13.65 ± 0.28 | 54.25 ± 1.33 | 109.13 ± 3.16 | 68.50 ± 2.12 | 50.18 ± 0.90 | 6.15 ± 0.22 | 3.11 ± 0.17 | 20.82 ± 0.86 | 5.44 ± 0.03 | 1.59 ± 0.06 |
| γ-Glu-Val-Gly | 0.64 ± 0.07 | LOD* | 0.47 ± 0.04 | 4.37 ± 0.10 | 5.38 ± 0.21 | 5.20 ± 0.15 | 5.34 ± 0.12 | 1.69 ± 0.02 | 1.40 ± 0.08 | 1.08 ± 0.08 | 1.57 ± 0.02 | 0.07 ± 0.02 |
| γ-Glu-Gly | 7.79 ± 0.21 | 3.52 ± 0.16 | 10.29 ± 0.29 | 5.54 ± 0.02 | 45.70 ± 1.23 | 30.24 ± 0.86 | 29.55 ± 0.84 | 8.43 ± 0.20 | 9.37 ± 0.12 | 12.33 ± 0.61 | 12.01 ± 0.12 | 4.18 ± 0.07 |
| γ-Glu-Gln | 7.00 ± 0.10 | LOD* | LOD* | 15.64 ± 0.10 | 8.84 ± 0.23 | 10.19 ± 0.18 | 12.39 ± 0.28 | 6.68 ± 0.25 | 7.64 ± 0.18 | 2.42 ± 0.08 | 6.82 ± 0.03 | 1.33 ± 0.02 |
| γ-Glu-His | 15.40 ± 0.15 | 0.69 ± 0.06 | 5.84 ± 0.26 | 80.33 ± 1.01 | 28.23 ± 0.63 | 20.44 ± 0.42 | 31.77 ± 0.88 | 6.082 ± 0.27 | 6.88 ± 0.42 | 10.35 ± 0.23 | 12.90 ± 0.05 | 1.96 ± 0.11 |
| γ-Glu-Glu | 36.071 ± 0.34 | 18.12 ± 0.65 | 33.471 ± 0.56 | 109.01 ± 2.11 | 213.65 ± 6.90 | 137.50 ± 2.16 | 139.66 ± 3.29 | 18.16 ± 0.66 | 23.61 ± 2.13 | 54.58 ± 2.50 | 31.48 ± 0.4 | 7.04 ± 0.46 |
| ∑ γ-Glu-X | 97.64 | 76.53 | 95.32 | 445.61 | 620.88 | 397.99 | 382.05 | 84.58 | 92.26 | 151.32 | 103.58 | 20.20 |
Values represent the mean ± standard deviation
LOD*; Limit of determination
Contents of GGPs in doenjang
The contents of GGPs in doenjang are summarized in Table 2. GGPs were present in all analyzed doenjang samples, and their contents ranged from 1,425.14 to 2,940.76 μg/g in traditional doenjang and from 1,425.14 to 14,464.75 μg/g in industrial doenjang. These results indicate that GGPs are commonly distributed in various types of doenjang. There was no obvious correlation between the contents and manufacturing types of doenjang. γ-Glu-Met (1.60-fold), γ-Glu-His (1.55-fold), γ-Glu-Glu (1.51-fold), γ-Glu-Leu (1.17-fold), γ-Glu-Val (1.15-fold), γ-Glu-Gln (1.10-fold) were determined at higher levels in traditional doenjang compared to industrial one.
Table 2.
Contents of GGPs in selected doenjang samples (μg/g)
| GGP | Traditional doenjang | Industrial doenjang | |||||||
|---|---|---|---|---|---|---|---|---|---|
| KT | MT | PT | ST | SC | HC | CC | KC | IC | |
| γ-Glu-Trp | 12.47 ± 1.21 | 9.82 ± 0.43 | 16.26 ± 0.09 | 5.80 ± 0.36 | 232.63 ± 9.80 | 8.19 ± 0.73 | 26.18 ± 0.86 | 7.578 ± 0.35 | 9.31 ± 0.23 |
| γ-Glu-Phe | 292.28 ± 21.03 | 559.42 ± 25.45 | 394.15 ± 18.19 | 393.72 ± 3.61 | 1551.04 ± 75.18 | 648.52 ± 44.32 | 761.02 ± 31.01 | 552.84 ± 14.35 | 822.32 ± 31.60 |
| γ-Glu-Leu | 79.30 ± 4.91 | 72.08 ± 3.49 | 173.55 ± 7.11 | 32.94 ± 0.46 | 1355.98 ± 62.59 | 11.33 ± 0.71 | 17.60 ± 0.24 | 241.81 ± 6.64 | 10.50 ± 0.30 |
| γ-Glu-Met | 65.52 ± 5.14 | 19.60 ± 0.87 | 87.11 ± 5.50 | 23.16 ± 0.34 | 568.99 ± 31.04 | 6.19 ± 0.56 | 10.75 ± 0.50 | 86.91 ± 2.36 | 6.43 ± 0.11 |
| γ-Glu-Tyr | 310.84 ± 21.42 | 567.54 ± 17.73 | 323.55 ± 11.57 | 366.21 ± 8.21 | 554.40 ± 19.74 | 493.48 ± 33.73 | 583.28 ± 15.15 | 429.68 ± 3.98 | 525.97 ± 18.36 |
| γ-Glu-Val | 188.21 ± 13.79 | 58.17 ± 2.18 | 239.26 ± 13.46 | 72.18 ± 1.02 | 1672.23 ± 90.81 | 16.36 ± 1.65 | 22.80 ± 0.84 | 393.98 ± 9.78 | 12.14 ± 0.49 |
| γ-Glu-Val-Gly | 17.73 ± 1.50 | 14.02 ± 1.00 | 25.17 ± 1.81 | 12.64 ± 0.33 | 52.23 ± 4.16 | 6.39 ± 0.98 | 7.298 ± 0.49 | 49.64 ± 0.70 | 4.62 ± 0.22 |
| γ-Glu-Gly | 259.54 ± 15.30 | 162.34 ± 4.66 | 280.21 ± 9.03 | 151.24 ± 5.04 | 857.78 ± 51.57 | 19.08 ± 2.28 | 25.40 ± 1.41 | 381.11 ± 6.58 | 23.60 ± 0.51 |
| γ-Glu-Gln | 107.06 ± 5.26 | 225.26 ± 6.43 | 123.48 ± 7.47 | 48.16 ± 1.97 | 168.76 ± 7.07 | 100.02 ± 7.98 | 149.09 ± 4.47 | 67.82 ± 0.67 | 103.25 ± 4.87 |
| γ-Glu-His | 200.78 ± 15.03 | 434.02 ± 12.13 | 422.65 ± 20.89 | 155.38 ± 4.05 | 3958.77 ± 166.22 | 80.37 ± 7.58 | 127.82 ± 6.00 | 432.71 ± 5.40 | 77.83 ± 4.23 |
| γ-Glu-Glu | 535.77 ± 36.16 | 818.49 ± 20.80 | 782.76 ± 35.61 | 163.71 ± 5.14 | 3491.96 ± 53.06 | 139.44 ± 9.5 | 286.89 ± 6.17 | 818.32 ± 14.52 | 154.34 ± 5.62 |
| ∑ γ-Glu-X | 2069.49 | 2940.76 | 2868.16 | 1425.14 | 14,464.75 | 1529.37 | 2018.14 | 3462.39 | 1750.32 |
Values represent the mean ± standard deviation
As expected based on kokumi-like taste of ganjang and doenjang, they contained various GGPs which might impart their kokumi taste (Tables 1 and 2). Regardless of manufacturing types, all analyzed ganjang and doenjang contained the analyzed eleven GGPs. To the best of our knowledge, only five kinds of GGPs have been reported in other soy sauces (Frerot and Chen, 2013; Kuroda et al., 2013) and GGPs in doenjang have not been reported. The previously reported GGPs such as γ-Glu-Glu, γ-Glu-Ile, γ-Glu-Leu, γ-Glu-Phe, and γ-Glu-Val-Gly in soy sauces were identified except for γ-Glu-Ile in ganjang. The fewer number of GGPs identified in other soy sauces may have resulted from limitations in the analysis methods, and other soy sauces may also contain additional GGPs as in ganjang. Our study was limited to the GGPs whose reference molecules were available. Therefore, ganjang and doenjang might contain other GGPs including γ-Glu-Ile which were not analyzed.
The contents of GGPs were higher in doenjang than ganjang by more than twofold. This may be a result due to differences in their manufacturing processes, in which ganjang uses only the liquid part of fermented soybeans in brine while doenjang is made of the solid portion of the fermented soybeans. This may explain why the taste of doenjang is described as more kokumi-like taste compared to ganjang by consumers.
Soybeans, the raw starting materials for ganjang and doenjang production, contain GGPs such as γ-Glu-Tyr and γ-Glu-Phe at variable levels depending on their origin (Shibata et al., 2018). Therefore, some GGPs may originate from the raw soybeans. However, the variable levels of GGPs amongst ganjang produced by the same manufacture suggest that the majority of them are produced during the manufacturing processes. Most GGPs in fermented foods are formed by microbial activity and enzyme present in the raw materials (Yang et al., 2019). Because all enzymes of soybeans are inactivated during boiling process before fermentation, microbial enzymes such as γ-glutamylpeptidase (GGT) and certain l-glutaminase may be responsible for the production of GGPs during fermentation. Several microorganisms are involved in ganjang and doenjang fermentation. Some microorganisms isolated from meju such as Aspergillus oryzae, Aspergillus sojae, Penicillium roqueforti exhibit GGT activity (unpublished data), suggesting that GGP in ganjang and doenjang samples are produced by enzyme activity of major fermenting microorganisms. Ganjang and doenjang are produced using traditional meju which is fermented by various microorganisms such as molds, yeasts, and bacteria, or using whole soybean meju which is usually fermented by a starter mold. Therefore, additional factors to microorganisms seem to be important for the contents of GGPs.
The taste of ganjang and doenjang has been described very abstractly as “gusuhada” in Korean which is very similar to kokumi taste. The main ingredients that contribute to this taste had not been recognized. This research confirmed that ganjang and doenjang contain various GGPs which could contribute to the unique taste of ganjang and doenjang.
Supplementary Information
Below is the link to the electronic supplementary material.
Acknowledgements
This work was supported by a grant from the National Research Foundation of Korea (nos. 2017R1A2B4004748 and 2021R1F1A1058263) and a Korea Environmental Industry and Technology Institute (KEITI) grant funded by the Ministry of Environment of Korea.
Declarations
Conflict of interest
The authors declare no conflict of interest.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Contributor Information
Hyun Jie Kim, Email: babahje@naver.com.
Do Yup Lee, Email: rome73@snu.ac.kr.
Inhyung Lee, Email: leei@kookmin.ac.kr.
References
- Desfontaine V, Goyon A, Veuthey J-L, Charve J. Development of a LC-MS/MS method for the determination of isomeric glutamyl peptides in food ingredients. Journal of Seperation Science. 2018;41:847–855. doi: 10.1002/jssc.201701182. [DOI] [PubMed] [Google Scholar]
- Frerot E, Chen T. Identification and quantitation of new glutamic acid derivatives in soy sauce by UPLC/MS/MS. Chemistry & Biodiversity. 2013;10:1842–1850. doi: 10.1002/cbdv.201300150. [DOI] [PubMed] [Google Scholar]
- Hillmann H, Behr J, Ehrmann M, Vogel R, Hofmann T. Formation of kokumi-enhancing γ-glutamyl dipeptides in parmesan chees by means of γ-glutamyltransferase activity and stable isotope double-labeling studies. Journal of Agricultural and Food Chemistry. 2016;64:1784–1793. doi: 10.1021/acs.jafc.6b00113. [DOI] [PubMed] [Google Scholar]
- Kuroda M, Kato Y, Yamazaki J, Kai Y, Mizukoshi T, Miyano H, Eto Y. Determination and quantification of the kokumi peptide, γ-glutamyl-valyl-glycine, in commercial soy sauces. Food Chemistry. 2013;141:823–828. doi: 10.1016/j.foodchem.2013.03.070. [DOI] [PubMed] [Google Scholar]
- Lee E-J, Kwon O-J, Choi U-K, Son D-H, Kwon O-J, Lee S-I, Yang S-H, Im M-H, Kim D-G, Chung Y-G. Changes in taste components of kanjang made with barly bran during fermentation. Korean Journal of Food Science and Technology. 2002;34:85–90. [Google Scholar]
- Lee EJ, Hyun J, Choi YH, Hurh BS, Choi SH, Lee I. Development of safe and flavor-rich doenjang (Korean fermented soybean paste) using autochthonous mixed starters at the pilot plant scale. Journal of Food Science. 2018;83:1723–1732. doi: 10.1111/1750-3841.14166. [DOI] [PubMed] [Google Scholar]
- Maruyama Y, Yasuda R, Kuroda M, Eto Y. Kokumi substances, enhancers of basic tastes, induce responses in calcium-sensing receptor expressing taste cells. PLoS One. 2012;7:e34489. doi: 10.1371/journal.pone.0034489. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ohsu T, Amino Y, Nagasaki H, Yamanaka T, Takeshita S, Hatanaka T, Maruyama Y, Miyamura N, Eto Y. Involvement of the calcium-sensing receptor in human taste perception. Journal of Biological Chemistry. 2010;285:1016–1022. doi: 10.1074/jbc.M109.029165. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Roudot-Algaron F, Kerhoas L, Bars D, Einhorn J, Gripon J. Isolation of γ-gluyamy peptides from comte cheese. Journal of Dairy Science. 1994;77:1161–1166. doi: 10.3168/jds.S0022-0302(94)77053-3. [DOI] [Google Scholar]
- Shibata M, Hirotsuka M, Mizutani Y, Takahashi H, Kawada T, Matsumiya K, Hayashi Y, Matsumura Y. Diversity of γ-glutamyl peptides and oligosaccharides, the "kokumi" taste enhancers, in seeds from soybean mini core collections. Bioscience, Biotechnology, and Biochemistry. 2018;82:507–514. doi: 10.1080/09168451.2018.1436960. [DOI] [PubMed] [Google Scholar]
- Shin D, Jeong D. Korean tranditional fermented soybean products: jang. Journal of Ethnic Foods. 2015;2:2–7. doi: 10.1016/j.jef.2015.02.002. [DOI] [Google Scholar]
- Toelstede S, Hofmann T. Kokumi-active glutamyl peptides in cheeses and their biogeneration by Penicillium roquefortii. Journal of Agricultural and Food Chemistry. 2009;57:3738–3748. doi: 10.1021/jf900280j. [DOI] [PubMed] [Google Scholar]
- Toelstede S, Dunkel A, Hofmann T. A series of kokumi peptides impart the long-lasting mouthfulness of matured Gouda cheese. Journal of Agricultural and Food Chemistry. 2009;57:1440–1448. doi: 10.1021/jf803376d. [DOI] [PubMed] [Google Scholar]
- Ueda Y, Sakaguchi M, Hirayama K, Miyajima R, Kimizuka A. Characteristic flavor constituents in water extract of garlic. Agricultural and Biological Chemistry. 1990;54:163–169. [Google Scholar]
- Ueda Y, Yonemitsu M, Tsubuku T, Sakaguchi M. Flavor characteristics of glutathione in raw and cooked foodstuffs. Bioscience, Biotechnology, and Biochemistry. 1997;61:1977–1980. doi: 10.1271/bbb.61.1977. [DOI] [PubMed] [Google Scholar]
- Yang J, Bai W, Zeng X, Gui C. Gamma glutamyl peptides: The food source, enzymatic synthesis, kokumi-active and the potential functional properties-A review. Trends in Food Science and Technology. 2019;91:339–346. doi: 10.1016/j.tifs.2019.07.022. [DOI] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.