Natural food and beverage flavour enhancers - Natural Food Additives, Ingredients and Flavourings - page 90

A more recent study by one of these research groups (Nakata et al. 1995)
investigated fi ve longer umami taste oligopeptides (Ser-Leu-Ala-Lys-Gly-Asp-
Glu-Glu, Ser-Leu-Ala-Asp-Glu-Glu-Lys-Gly, Lys-Gly-Ser-Leu-Ala-Asp-Glu-
Glu, Lys-Gly-Asp-Glu-Glu and Glu-Glu-Asp-Gly-Lys) and the effects of basic
(Lys-Gly) and acidic (Asp-Glu-Glu) fragments. They found that the umami
intensity and/or salty taste of the peptides and their sodium salts were almost the
same, despite their chemical structures being different. This indicated that the
acidic and basic fragments were important in the taste intensity of delicious
peptides. It also implied that an umami or salty taste could be produced by the
placing a cation of the basic fragment and an anion of the acidic fragment.
The existence of any umami peptide was refuted by van den Oor and van
Wassenaar (1997) who selected 12 dipeptides and four tripeptides from the
31 umami di- and tripeptides discussed above for taste evaluation by a sensory
panel; none were found to have an umami taste. As mentioned above, many small
peptides exist within soy sauces, but the Lioe research group has concluded that
these have a very low and non-signifi cant effect on umami taste (Lioe et al. 2010).
However, work in Japan had continued. Maehashi et al. (1999) investigated four
protein sources (soy bean, casein, bonito and chicken) hydrolysed by four enzymes
(pepsin, trypsin, α -chymotrypsin and bromelain). The chicken protein hydrolysate
from bromelain had the best umami taste and was therefore studied further. Eleven
peptides were isolated from the hydrolysate, many of which did not stimulate an
umami taste alone. However, a few of the peptides (notably Glu-Glu, Glu-Val,
Asp-Glu-Glu and Glu-Glu-Asn) substantially enhanced the umami taste of a
0.02% IMP solution.
Since then the Hofmann group in Germany has also identifi ed umami peptides.
For example, in a study to investigate why an aqueous extract from beans
( Phaseolus vulgaris ) enhanced the mouthfulness and complexity, and led to a
longer lasting savoury taste when added to a model chicken broth, three glutamyl
peptides were identifi ed as responsible (Dunkel et al. 2007). γ - L -Glutamyl- L -
leucine, γ - L -glutamyl- L -valine and γ - L -glutamyl-L-cysteinyl- β -alanine were
found to be predominantly tasteless in isolation but to reduce the taste threshold
of a glutamic acid/sodium chloride mixture as well as impart mouthfulness,
thickness and a prolonged taste profi le. They were therefore also described as
'kokumi' peptides. The term kokumi is typically used to describe a sensation of
'richness' and 'mouthfulness'. In a later study of Gouda cheese, the researchers
noted a distinct increase in mouthfulness, taste duration and complexity in mature
cheese compared to young cheese. Six 'kokumi' glutamyl dipeptides were held
responsible: γ -Glu-Glu, γ -Glu-Gly, γ -Glu-Gln, γ -Glu-Met, γ -Glu-Leu, and γ -Glu-
His (Toelstede et al. 2009).
More recently, three β -alanyl-dipeptides ( β -alanyl- N -methyl- L -histidine,
β -alanyl- L -histidine and β -alanylglycine) have been identifi ed as taste enhancers
in chicken broth; enhancing a white-meaty sensation as well as a thick-sour
sensation (Dunkel and Hofmann 2009). In combination with glutamic acid and
sodium or potassium ions, the sensory characteristics were enhanced. In isolation
these peptides had a slight sour and astringent taste.

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