38 1 Amino Acids, Peptides, Proteins
Table 1.16.Taste of dipeptide esters of aspartic acida
and of amino malonic acidb
R^2 R^3 Tastec
Asparagin acid derivate
COOCH 3 H8
n-C 3 H 7 COOCH 3 4
n-C 4 H 9 COOCH 3 45
n-C 4 H 9 COOC 2 H 5 5
n-C 6 H 13 CH 3 10
n-C 7 H 15 CH 3 neutral
COOCH(CH 3 ) 2 n-C 3 H 7 17
COOCH(CH 3 ) 2 n-C 4 H 9 neutral
COOCH 3 CH 2 C 6 H 5 bitter
CH(CH 3 )C 2 H 5 COOCH 3 bitter
CH 2 CH(CH 3 ) 2 COOCH 3 bitter
CH 2 C 6 H 5 COOCH 3 140
COO-2-methyl-
cyclohexyl COOCH 3 5–7000
COO-fenchyl COOCH 3 22–33, 000
D,L-Aminomalon acid derivate
COOiC 3 H 7 CH 3 58
CH 3 COOiC 3 H 7 neutral
aFormula 1.77 I, R (^1) =H.
bFormula 1.77 II, R (^1) =H.
cFor sweet compounds the factor fsac, gis given, re-
lated to the threshold value of a 10% saccharose solu-
tion (cf. 8.8.1.1).
The intensity of the salty taste of Orn-β-Ala de-
pends on the pH (Table 1.18). Some peptides
exhibit a salty taste, e. g. ornithyl-β-alanine hy-
drochloride (Table 1.17) and may be used as sub-
stitutes for sodium chloride.
Table 1.17.Peptides with a salty taste
Peptidea Taste
Threshold Qualityb
(mmol/l)
Orn-βAla.HCl 1. 25 3
Orn-γAbu.HCl 1. 40 3
Orn-Tau.HCl 3. 68 4
Lys-Tau.HCl 5. 18 4
NaCl 3. 12 3
a Abbreviations: Orn, ornithine; β-Ala, β-alanine,
γ-Abu,γ-aminobutyric acid; Tau, taurine.
bThe quality of the salty taste was evaluated by rating it
from 0 to 5 on a scale in comparison with a 6.4 mmol/L
NaCl solution (rated 3); 4 is slightly better, 5 clearly
better than the control solution.
Table 1.18.Effect of HCl on the salty taste of Orn-β-
Alaa
Equivalents pH Taste
HCl
saltyb sourc
08. 90
0. 79 7. 00
0. 97 6. 01
- 00 5. 52
- 10 4. 73 +/−
- 20 4. 33. 5 +
- 30 4. 23 ++
aPeptide solution: 30 mmol/L.
bThe values 1, 3 and 5 correspond in intensity to 0.5%,
0 .25% and 0.1% NaCl solutions respectively.
cVery weak(+)and slightly sour (++).
1.3.4 IndividualPeptides......................................
Peptides are widespread in nature. They are often
involved in specific biological activities (peptide
hormones, peptide toxins, peptide antibiotics).
A number of peptides of interest to food chemists
are outlined in the following sections.1.3.4.1 Glutathione
Glutathione (γ-L-glutamyl-L-cysteinyl-glyci-ne)
is widespread in animals, plants and microorgan-
isms. Beef (200), broccoli (140), spinach (120),
parsley (120), chicken (95), cauliflower (74),
potatoes (71), paprika (49), tomatoes (49)
and oranges (40) are especially rich in glu-
tathione (mg/kg). A noteworthy feature is
the binding of glutamic acid through its γ-
carboxyl group. The peptide is the coenzyme of
glyoxalase.(1.78)It is involved in active transport of amino
acids and, due to its ready oxidation, is also
involved in many redox-type reactions. It in-
fluences the rheological properties of wheat
flour dough through thiol-disulfide interchange
with wheat gluten. High concentrations of re-
duced glutathione in flour bring about reduction