Molecular and Sensory Characterization of γ-Glutamyl Peptides as Key Contributors to the Kokumi Taste of Edible Beans (Phaseolus vulgaris L.)

Abstract

Addition of a nearly tasteless aqueous extract isolated from beans (Phaseolus vulgaris L.) to a model chicken broth enhanced its mouthfulness and complexity and induced a much more long-lasting savory taste sensation on the tongue. Gel permeation chromatography and hydrophilic interaction liquid chromatography/comparative taste dilution analysis (HILIC/cTDA), followed by LC-MS/MS and 1D/2D-NMR experiments, led to the identification of gamma-L-glutamyl-L-leucine, gamma-L-glutamyl-L-valine, and gamma-L-glutamyl-L-cysteinyl-beta-alanine as key molecules inducing this taste-modifying effect. Sensory analysis of aqueous solutions of these peptides showed threshold concentrations between 3.3 and 9.4 mmol/L for an unspecific, slightly astringent sensation. More interestingly, when added to a savory matrix such as sodium chloride and monosodium glutamate solutions or chicken broth, the detection thresholds of these gamma-glutamyl peptides decreased significantly and remarkably enhanced mouthfulness, complexity, and long-lastingness of the savory taste were observed; for example, the threshold of gamma-glutamyl-cysteinyl-beta-alanine decreased by a factor of 32 in a binary mixture of glutamic acid and sodium chloride. As tasteless molecules inducing mouthfulness, thickness, and increasing continuity of savory foods were coined about 10 years ago as "kokumi" flavor compounds, the peptides identified in raw as well as thermally treated beans have to be considered as kokumi compounds.

Increase of “Umami” and “Kokumi” Compounds in Miso, Fermented Soybeans, by the Addition of Bacterial γ-Glutamyltranspeptidase

“…"Kokumi" substances themselves do not have a "kokumi" taste, but the addition of a small amount of these substances enhances the flavour of food by inducing persistence, depth, and mouth-fullness. It was reported that some γ-glutamyl compounds, such as GSH, are "kokumi" substances (Dunkel, Koester, & Hofmann, 2007;Toelstede, Dunkel, & Hofmann, 2009;). Ohsu et al (2010) compared the enhancement of "kokumi" by various γ-glutamyl compounds and found that γ-Glu-Val-Gly is the strongest "kokumi" substance.…”

Evaluation of wheat gluten hydrolysates as taste-active compounds with antioxidant activity

“…In particular, hydrophobic amino acids such as Pro, Gly, Ala, Val, Met, Ile, Leu, and Phe in the WGHs treated with Flavourzyme or Protamex increased as the hydrolysis time was prolonged to 24 h. In general, glutamic acid is an important compound of umami taste (Aaslyng et al 1998). Dunkel et al (2007) indicated that savory compounds such as sodium chloride and L-glutamic acid were able to increase the kokumi. Nishiwaki et al (2002) also proposed that the hydrophobic peptides contribute to bitter taste.…”

“…On the other hand, kokumi means "rich," and taste continuity derived from amino acids and peptides (Hedwig and Amado 2002). Dunkel et al (2007) …”

Identification of Low Molecular Weight Peptides in Chinese Rice Wine (Huang Jiu) by UPLC-ESI-MS/MS

“…Hofmann's research group has found many key bitter and kokumi peptides in Gouda cheeses and edible beans 7,34,35 . Hashizume et al 10 reported that five peptides isolated from sake presented the unpleasant taste with an accompanying bitter taste.…”