Effect of a kokumi peptide, γ-glutamyl-valyl-glycine, on the sensory characteristics of chicken consommé
© Miyaki et al.; licensee BioMed Central. 2015
Received: 3 September 2014
Accepted: 1 December 2014
Published: 26 January 2015
Recent studies have demonstrated that kokumi substances such as glutathione are perceived through the calcium-sensing receptor (CaSR). Screening by a CaSR assay and sensory evaluation have shown that γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly) is a potent kokumi peptide. In the present study, the sensory characteristics of chicken consommé with added γ-Glu-Val-Gly were investigated using descriptive analysis.
Chicken consommé containing γ-Glu-Val-Gly had significantly stronger “umami” and “mouthfulness” (mouth-filling sensation) characteristics than the control sample at a 99% confidence level and significantly stronger “mouth-coating” characteristic than controls at a 95% confidence level.
These data suggest that a kokumi peptide, γ-Glu-Val-Gly, can enhance umami, mouthfulness, and mouth coating, implying that the application of this peptide could contribute to improving the flavor of chicken consommé.
KeywordsChicken consommé Kokumi γ-Glutamyl-valyl-glycine γ-Glu-Val-Gly Sensory evaluation Descriptive analysis
Taste and aroma are important factors in determining the flavor of foods. Sweet, salty, sour, bitter, and umami comprise the five basic tastes with each taste being recognized by specific receptors and associated with particular transduction pathways. However, foods have sensory attributes that cannot be explained by aroma and the five basic tastes alone: texture, continuity, complexity, and mouthfulness. Ueda et al. investigated the flavoring effects of a diluted extract of garlic that enhanced continuity, mouthfulness, and thickness when added to an umami solution and attempted to isolate and identify the key compounds responsible for this effect . Their study indicated that sulfur-containing compounds such as S-allyl-cysteine sulfoxide (alliin), S-methyl-cysteine sulfoxide, γ-glutamyl-allyl-cysteine, and glutathione (γ-glutamyl-cysteinyl-glycine; GSH) led to this flavoring effect. These compounds have only a minimal flavor in water, but if added to an umami solution or other types of food, they can substantially enhance the thickness, continuity, and mouthfulness of the food to which they have been added . They proposed that substances with these properties should be referred to as kokumi substances.
Recently, it was reported that kokumi substances such as GSH are perceived through the calcium-sensing receptor (CaSR) in humans . These studies confirmed that GSH can activate human CaSR, as can several γ-glutamyl peptides, including γ-Glu-Ala, γ-Glu-Val, γ-Glu-Cys, γ-Glu-α-aminobutyryl-Gly (ophthalmic acid), and γ-Glu-Val-Gly. Furthermore, these compounds have been shown to possess the characteristics of kokumi substances, which modify the five basic tastes (especially sweet, salty, and umami) when added to basic taste solutions or food, even though they have no taste themselves at the concentrations tested [1, 2, 4–8]. The CaSR activity of these γ-glutamyl peptides has also been shown to be positively correlated with the sensory activity of kokumi substances, suggesting they are perceived through the CaSR in humans. Among these, γ-Glu-Val-Gly has been reported to be a potent kokumi peptide with a sensory activity 12.8-fold times greater than that of GSH . Additionally, it has been reported that γ-Glu-Val-Gly was present in several foods such as scallops , fermented fish sauces , soy sauces , and fermented shrimp pastes . Ohsu et al. also reported that adding 0.01% γ-Glu-Val-Gly to 3.3% sucrose solution, 0.9% NaCl solution, and 0.5% monosodium glutamate (MSG) solution significantly enhanced sweetness, saltiness, and umami, respectively . They also reported that adding 0.002% γ-Glu-Val-Gly to chicken consommé prepared from commercial chicken consommé powder significantly enhanced thickness, continuity, and mouthfulness. In that report, sensory evaluation was undertaken with sensory attributes with reference to a method reported previously [1, 2]. The sensory attributes used in these previous research works such as thickness, mouthfulness, and continuity were originally extracted using the sensory evaluation which compared the sensory profiles of various foods, mainly soups, with and without MSG . Therefore, to clarify the sensory characteristics of food with added γ-Glu-Val-Gly, a more detailed study comparing the sensory attributes of food with and without this peptide has been needed.
In the present study, we aim to characterize the sensory properties of food with added γ-Glu-Val-Gly, through performing a descriptive analysis of chicken consommé containing the peptide.
Results and discussion
Sensory attributes for chicken consommé
Definition and reference samples for the descriptive attributes of chicken consommé
Reference samples and intensity
The total intensity of all of the flavors of the sample including basic tastes
Kitchen Basics chicken broth (6)
Total chicken/meaty flavor
The flavor intensity reminiscent of cooked chicken meat
Kitchen Basics chicken broth (5)
The flavor intensity reminiscent of cooked chicken
Kitchen Basics chicken broth (5)
The character associated with chicken bones, particularly the marrow of chicken bones
The total flavor intensity that is reminiscent of roasted chicken and/or vegetables
Swanson’s chicken broth (6)
Total vegetable flavor
The total flavor intensity of vegetables such as carrots, green vegetables, and herbs in the broth
Kitchen Basics chicken broth (5)
The degree to which the flavor characters of the sample are harmonized, balanced, and blend well together as opposed to being spiky or striking out
One of the basic taste, common to sodium chloride
0.2% sodium chloride in water (2) 0.5% sodium chloride in water (5) 0.2% sodium chloride in water (2) 0.5% sodium chloride in water (5)
One of the basic taste, common to MSG. The taste and mouth-filling sensation of compounds such as glutamates that is savory, brothy, meaty, rich, full, and complex, common to many foods such as soy sauce, stocks, ripened cheese (especially parmesan), shellfish (crab, lobster, scallops, clams), mushrooms (especially porcini), ripe tomatoes, cashews, and asparagus
Kitchen Basics chicken broth (2) 0.5% MSG in Kitchen Basics chicken broth (3.5) Kitchen Basics chicken broth (2) 0.5% MSG in Kitchen Basics chicken broth (3.5)
The degree to which the samples are viscous in the mouth from thin to thick
Water (1) Heavy whipping cream (6)
The perception that the sample fills the whole mouth is blooming, or growing, a full-bodied sensation when the sample is held in the mouth
Kitchen Basics chicken broth (1.5) 0.5% MSG in Kitchen Basics chicken broth (3) Kitchen Basics chicken broth (1.5) 0.5% MSG in Kitchen Basics chicken broth (3)
The degree to which there is a leftover residue, a slick, powdery, or fatty coating or film in the mouth that is difficult to clear
0.5% MSG in water (4) Half and Half (5) 0.5% MSG in water (4) Half and Half (5)
The degree to which there is a leftover residue, a slick, powdery, or fatty coating or film on the tongue that is difficult to clear
0.5% MSG in water (3)
The intensity of the total sensation, including numbing, burning, tingling, or irritation, impaired on the soft tissues of the oral cavity, particularly the tongue
Wintergreen breathsaver (NS) 0.5% MSG in water (5) Wintergreen breathsaver (NS) 0.5% MSG in water (5)
The degree to which the sample caused a perceived increase in salivation
Swelling of cheeks and lips
The feeling of swelling of the soft tissue in the oral cavity, specifically the cheeks and lips, reminiscent of the perception of swelling produced by antithetic treatments at a dental office, but without a distinct numbing effect
0.5% MSG in water (4)
The total aftertaste intensity after 5 s of all flavor notes within the sample
Sensory characteristics of chicken consommé with added γ-Glu-Val-Gly
Consomme with γ-Glu-Val-Gly
95% confidence interval
99% confidence interval
6.13 ± 0.72
6.31 ± 0.68
0.18 ± 0.60
Total chicken/meaty flavor
5.26 ± 0.61
5.41 ± 0.59
0.14 ± 0.59
4.82 ± 0.55
4.88 ± 0.78
0.06 ± 0.69
2.42 ± 0.85
2.63 ± 0.98
0.21 ± 1.14
3.19 ± 1.03
3.12 ± 1.03
-0.07 ± 0.82
Total vegetable flavor
3.56 ± 0.75
3.78 ± 0.81
0.22 ± 0.64
4.01 ± 0.81
4.27 ± 0.94
0.27 ± 0.79
2.73 ± 0.48
2.87 ± 0.73
0.13 ± 0.57
2.84 ± 0.65
3.28 ± 0.67
0.43 ± 0.66
2.06 ± 0.65
2.22 ± 0.59
0.16 ± 0.40
2.47 ± 0.70
2.92 ± 0.73
0.45 ± 0.69
2.67 ± 0.66
2.94 ± 0.65
0.27 ± 0.56
2.56 ± 0.82
2.72 ± 0.82
0.17 ± 0.68
2.42 ± 0.85
2.58 ± 0.83
0.16 ± 1.06
2.76 ± 0.87
2.98 ± 0.73
0.23 ± 0.84
Swelling perception of soft tissue
2.78 ± 0.79
2.87 ± 0.68
0.09 ± 0.76
4.46 ± 0.60
4.54 ± 0.66
0.08 ± 0.64
Sensory characteristics of chicken consommé with added γ-Glu-Val-Gly
Interestingly, the present study has revealed that the addition of γ-Glu-Val-Gly at 5 ppm significantly enhanced the intensity of mouth coating. It has been generally known that mouth-coating sensation is evoked by the addition of hydrocolloids such as xanthan gum and locust bean gum, carrageenan [14, 15], and fat-containing food materials such as dairy fat emulsion . However, several studies have reported that low-molecular-weight compounds enhanced the intensity of mouth coating. Dawid and Hofmann reported that 1,2-dithiolan-4-carboxylic acid 6-d-glucopyranoside ester exhibited a buttery mouth-coating sensation . Additionally, the same research group demonstrated that polyphenolic compounds such as vanillin, vanillin-related compounds, americanin A, and 4′,6′-dihydroxy-3′,5′-dimethoxy-[1,1′-biphenyl]-3-carboxaldehyde from cured vanilla beans exhibited a velvety mouth-coating sensation . Furthermore, it has been reported that the flavon-3-ol glycosides such as kaempferol glycosides, quercetin glycosides, myricetin glycosides, and apigenin glycoside from black tea induced a mouth-coating sensation . Despite these observations, there have been no reports of a peptide which exhibited the mouth-coating sensation. Therefore, this is the first report which has demonstrated the mouth-coating effect of peptides. Although the viscosity of consommé did not change significantly by adding 5 ppm of γ-Glu-Val-Gly (data not shown), an enhancement of the mouth-coating sensation was observed. The mechanism of this enhancement is interesting and should be clarified by further investigations.
Contents of free amino acids and 5′-nucleotide in chicken consomme
The addition of γ-Glu-Val-Gly significantly enhanced the intensity of umami, mouthfulness, and mouth coating in chicken consommé. The results suggest that adding γ-Glu-Val-Gly can improve the flavor and mouthfeel of chicken consommé. To confirm this possibility, consumer preferences for chicken consommé with added γ-Glu-Val-Gly are now being investigated in our laboratory.
In the present study, the sensory characteristics of chicken consommé with 5.0 ppm added γ-Glu-Val-Gly were investigated using descriptive analysis. Chicken consommé containing γ-Glu-Val-Gly had significantly stronger “umami” and “mouthfulness” (mouth-filling sensation) characteristics than the control sample at a 99% confidence level and significantly stronger “mouth-coating” characteristic than the control at a 95% confidence level. These data indicated that a kokumi peptide, γ-Glu-Val-Gly, can enhance umami, mouthfulness, and mouth coating in chicken consommé. From these results, it was suggested that the addition of γ-Glu-Val-Gly can improve the flavor and mouthfeel of chicken consommé.
Preparation of γ-Glu-Val-Gly
The γ-Glu-Val-Gly used in the present study was of food additive grade (FEMA-GRAS No. 4709; JECFA food flavoring No. 2123) obtained from Ajinomoto Co., Inc. (Tokyo, Japan) and was prepared by a chemical synthetic method reported previously .
Preparation of chicken consommé
Raw materials for the chicken consommé
Chicken breast meat (minced)
Chicken leg meat (minced)
Chicken wing meat (minced)
Bouillon (Kisco Co., Inc.)
Selection of the panel
Eighteen female panelists participated in the sensory evaluation. The age of the panelists was 54.0 ± 8.8 (mean ± standard deviation) years old. They all live in the San Francisco Bay Area, CA, USA. The screening of the panelists was conducted in three phases: phone screening of applicants, on-site acuity testing, and face-to-face interviews with advanced acuity testing.
Training of the panel
General panel training
All of the panelists were broadly trained in sensory descriptive analysis to evaluate aromas, flavors, textures, and appearance across a wide range of consumer products. This training was conducted for approximately 3 days per week for 3 months, during which the panelists expanded their food sensory vocabularies, learned to use a 15-point scale to rate attribute intensities, and evaluated a wide variety of foods. For example, the sweetness intensity scale was anchored with several concentrations of sucrose in water and the intensity of “sweet aromatic” was anchored with several concentrations of vanilla in milk. The panelists-in-training refined their skills by participating in practice tests using many different types of products. After each test, they were given detailed feedback while retesting the products to help them improve their performance. After this training was complete, the panelists were registered as members of the Descriptive Panel of The National Food Laboratory and began to participate in the descriptive analysis of various kinds of foods.
Ongoing panelist feedback
Feedback was routinely provided during panel sessions to maintain and refine the evaluating ability of the panelists. Several times a month, the panelists were given face-to-face performance feedback to help them maintain their calibration. A panel leader tasted the products with the panelists as they reviewed their scores to highlight potential areas for improvement. Feedback was given both on discrimination among products and consistency between replications.
Project-specific orientation sessions
The objectives of the orientation training sessions were to understand the effect of γ-Glu-Val-Gly on chicken consommé to generate the list of sensory attributes for the evaluation sessions. This 2-h training session was conducted on the day before the sensory evaluation for the present study. During the session, panelists evaluated samples of chicken consommé with and without γ-Glu-Val-Gly to understand the effect of γ-Glu-Val-Gly. A panel leader led the group in discussion on the differences and similarities between the samples. They developed a list of sensory attributes that described the products’ sensory characteristics, focusing on attributes believed to be influenced by γ-Glu-Val-Gly. Each sample was tested at least twice during this orientation session. During this training session, the panelists also developed new attributes such as “total chicken/meaty flavour”, “bones/marrow flavour”, “roasted flavour”, “richness”, “tongue-coating”, and “salivating”. Overall, the panelists defined the 17 sensory attributes listed in Table 2. The panelists practiced rating the samples on the list so that they were prepared to begin data collection.
Project-specific panelist feedback
Between each of the six data collection replications, panelists were given feedback about the samples they had evaluated. A panel leader led the group in brief discussions on the differences and similarities between the samples. Panelists were instructed to taste samples (with and without 5 ppm γ-Glu-Val-Gly) for training purposes during the discussions. After each feedback discussion, the panelists took a 10-min break before data collection for the next replication.
Procedure for sensory evaluation
For the evaluation of chicken consommé, panelists held the product in the mouth for 10 s, expectorated, and then rated flavor, texture/mouthfeel, and aftertaste attributes. They then completed the rating for each attribute (samples with and without 5 ppm γ-Glu-Val-Gly) on a 15-point line scale. The sample serving order was balanced, with each sample being presented approximately an equal number of times in each position for each test. Two days of data collection were completed, each consisted of three replications. Feedback to the panelists was provided after each replication except the final replication. In total, six evaluations were conducted. In the present report, to investigate the effect of γ-Glu-Val-Gly on chicken consommé by an experimental protocol after a single feedback session, we report the result of the second replication of sensory evaluation data, which followed the first panelist feedback session on the first day of data collection. Human sensory analyses were conducted following the spirit of the Helsinki Declaration, and informed consent was obtained from all panelists. The experimental protocol was approved by the ethics board of the Institute of Food Sciences and Technologies, Ajinomoto.
Analyses of free amino acids and 5′-nucleotides in chicken consommé
Free amino acids were determined using a Model L-8800 amino acid analyzer (Hitachi Corp., Tokyo, Japan) with a lithium citrate buffer (PF-series for nonhydrolyzed amino acid analysis; Mitsubishi Chemical, Tokyo, Japan). The contents of 5′-nucleotides were determined by HPLC equipped with a Hitachi #3013 column with detection at 254 nm.
Statistical analyses were conducted using JMP version 9.0 (SAS Institute Inc., Cary, NC, USA). The data were collected as the means ± standard deviation. Data were assessed by the paired t test. The data was considered to be significant when the confidence level was more than 95%.
Flavour and Extract Manufacturers Association
The Joint FAO/WHO Expert Committee
We sincerely thank Dr. Kiyoshi Miwa and Dr. Yuzuru Eto of Ajinomoto Co., Inc. for their encouragement and continued support of this work. We are grateful to Mr. Jiro Sakamoto of Ajinomoto North America LLC for his valuable discussion and assistance. We thank Ms. Sharon McEvoy, previously of the National Food Laboratory LLC, for her cooperation and a valuable discussion, and to the panelists who have participated on the sensory evaluation. We are grateful to Dr. Chinatsu Kasamatsu, Mr. Hiroaki Nagasaki, Mr. Toshifumi Imada, Mr. Takaho Tajima, Mr. Shuichi Jo, Mr. Keita Sasaki, and Ms. Takako Hirose of Ajinomoto Co., Inc. for their assistance. There is no funding in the present study.
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