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38 1 Amino Acids, Peptides, Proteins

Table 1.16. Taste of dipeptide esters of aspartic acid a

and of amino malonic acid b

R 2 R 3 Taste c

Asparagin acid derivate

COOCH 3 H 8

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-methylcyclohexyl

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

a Formula 1.77 I, R 1 = H.

b Formula 1.77 II, R 1 = H.

c For sweet compounds the factor f sac, g is given, related

to the threshold value of a 10% saccharose solution

(cf. 8.8.1.1).

The intensity of the salty taste of Orn-β-Ala depends

on the pH (Table 1.18). Some peptides

exhibit a salty taste, e. g. ornithyl-β-alanine hydrochloride

(Table 1.17) and may be used as substitutes

for sodium chloride.

Table 1.17. Peptides with a salty taste

Peptide a

Taste

Threshold

(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

Quality b

Abbreviations: Orn, ornithine; β-Ala, β-alanine,

γ-Abu, γ-aminobutyric acid; Tau, taurine.

b The 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-

Ala a

Equivalents pH Taste

HCl

salty b sour c

0 8.9 0

0.79 7.0 0

0.97 6.0 1

1.00 5.5 2

1.10 4.7 3 +/−

1.20 4.3 3.5 +

1.30 4.2 3 ++

a Peptide solution: 30 mmol/L.

b The values 1, 3 and 5 correspond in intensity to 0.5%,

0.25% and 0.1% NaCl solutions respectively.

c Very weak (+) and slightly sour (++).

1.3.4 Individual Peptides

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 microorganisms.

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 glutathione

(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 influences

the rheological properties of wheat

flour dough through thiol-disulfide interchange

with wheat gluten. High concentrations of reduced

glutathione in flour bring about reduction

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