Mechanism of the perception of “kokumi” substances and the sensory characteristics of the “kokumi” peptide, γ-Glu-Val-Gly
© Kuroda and Miyamura; licensee BioMed Central Ltd. 2015
Received: 2 December 2014
Accepted: 2 December 2014
Published: 23 February 2015
Some foods are known to have flavours that cannot be explained by the five basic tastes alone, such as continuity, mouthfulness and thick flavour. It was demonstrated that these sensations are evoked by the addition of kokumi substances, flavour modifiers that have no taste themselves. However, their mode of action has been poorly understood. During a study on the perception of amino acids and peptides, it was found that glutathione (GSH) was one of the agonists of the calcium-sensing receptor (CaSR). We have hypothesized that CaSR is involved in the perception of kokumi substances. We found that all CaSR agonists tested act as kokumi substances and that a positive correlation exists between the CaSR activity of γ-glutamyl peptides and kokumi intensity. Furthermore, the kokumi intensities of GSH and γ-Glu-Val-Gly, a potent kokumi peptide, were significantly reduced by the CaSR-specific antagonist, NPS-2143. These results suggest that CaSR is involved in the perception of kokumi substances. A potent kokumi peptide, γ-Glu-Val-Gly, enhanced sweetness, saltiness and umami when added to 3.3% sucrose, 0.9% NaCl and 0.5% MSG solutions, respectively. In addition, γ-Glu-Val-Gly enhanced the intensity of continuity, mouthfulness and thick flavour when added to chicken soup and reduced-fat cream. These results suggest that γ-Glu-Val-Gly is a potent kokumi peptide and would be useful for improving the flavour of food.
KeywordsCalcium-sensing receptor Glutathione Thick flavour
Recent developments in molecular biology have demonstrated that the five basic tastes, sweet, salty, sour, bitter and umami are recognized by specific receptors and transduction pathways . However, some foods are known to have flavours that cannot be explained by the five basic tastes alone, such as continuity, mouthfulness and thick flavour. Ueda et al. have previously investigated the flavouring effect of garlic extract that enhanced continuity, mouthfulness and thick flavour when it was added to an umami solution . These authors demonstrated that several sulphur-containing compounds, identified as S-allyl-cysteine sulfoxide (alliin) and glutathione (GSH, γ-Glu-Cys-Gly), were responsible for this effect . Although these compounds have only a slight flavour in water, they substantially enhance the continuity, mouthfulness and thick flavour when added to an umami solution or various foods . They proposed that substances with these properties should be referred to as “kokumi” substances. However, their mode of action has been poorly understood. In this study, we aimed to clarify the mechanism of the perception of kokumi substances and the sensory characteristics of the potent kokumi peptide, γ-Glu-Val-Gly.
Mechanism of the perception of kokumisubstances
Sensory characteristics of the “kokumi” peptide, γ-Glu-Val-Gly
The kokumi intensity of γ-Glu-Val-Gly was measured by the point of substantial equivalent (PSE) method described previously . The sensory evaluation demonstrated that 0.01% solution of γ-Glu-Val-Gly produced a kokumi equivalent to a GSH solution of 0.128%. Therefore, we estimated that the kokumi intensity of γ-Glu-Val-Gly was 12.8 times stronger than that of GSH . This result suggests that γ-Glu-Val-Gly is a potent kokumi substance.
Next, we investigated the effect of γ-Glu-Val-Gly on the basic tastes (sweet, salty and umami). As results of the sensory evaluation with the trained panelists (n = 20), the addition of 0.01% γ-Glu-Val-Gly significantly enhanced the intensity of sweetness, saltiness and umami , although they have no taste themselves (data not shown). These results suggested that γ-Glu-Val-Gly has a property of kokumi substances.
In this study, the mechanism of the perception of kokumi substances was investigated. All CaSR agonists were kokumi substances, and a CaSR-specific antagonist decreased the kokumi intensity. Further, the CaSR activity correlated with the kokumi intensity. These results suggest that CaSR is involved in the perception of kokumi substances. Sensory analyses revealed that γ-Glu-Val-Gly had a kokumi intensity 12.8 times stronger than that of GSH and that it enhanced intensities of mouthfulness, thickness (or thick flavour) and continuity of food, suggesting that γ-Glu-Val-Gly is a potent kokumi substance.
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 Dr. Tohru Kouda, Dr. Yusuke Amino, Dr. Yutaka Maruyama, Dr. Toshihiro Hatanaka, Mr. Hiroaki Nagasaki, Mr. Tomohiko Yamanaka, Mr. Sen Takeshita, Dr. Takeaki Ohsu and Mr. Shuichi Jo of Ajinomoto Co. Inc. for their assistance. There is no funding in the present study.
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