Food Chemistry

286 4 Carbohydrates

(4.96)

Pyridosine (Formula 4.95) is also formed by
the degradation of Nε-fructoselysine, but in
lower amounts than furosine (ratio ca. 3:1). It is
assumed that 1-deoxyosone is the precursor.
Carboxymethyllysine is also formed from Nε-
fructoselysine and is also used as an indicator
of the degree of thermal treatment of protein
containing foods. This compound can be pro-
duced in different ways starting with oxidized
Nε-fructoselysine or the reaction of glyoxal with
the lysine side chain. The reaction path shown
in Formula 4.97 takes into account general
mechanisms of carbohydrate degradation with
cleavage ofβ-dicarbonyl compounds.
Pyrraline (Formula 4.95) is also formed as a mod-
ification of the amino acid lysine in proteins. The
reaction partner is, according to Formula 4.61,
3,4- dideoxyosone obtained from 4-deoxyosone.
Pyrraline is found in high concentrations espe-
cially in foods that have been subjected to strong
thermal treatment, e. g., biscuits and pastries
(Table 4.14). The concentrations in milk are
clearly less than those of furosine (Table 4.13).

The cross-linkage of proteins is also possible via
the pyrrole residues of 2 molecules of pyrraline.
The corresponding dimers have already been
detected in model reactions. (cf. Formula 4.100).
The amino acid arginine can also be modified
at the guanidino group, e. g., by reaction with
α-dicarbonyl compounds from carbohydrate
degradation. The compounds characterized
were, among others, those formed from the
reaction with methylglyoxal (I, Formula 4.98),
3-deoxyosone (II, Formula 4.98), a pentan-

Table 4.14.Concentrations of pyrraline in foods

Foods Pyrraline (mg/kg protein)

UHT milk <2–5

Sterile milk 60–80

Condensed milk 30–135

Pretzels 220–230

White bread crust 540–3680

White bread crumb 25–110

Nibbling biscuits 970–1320

dione (III, Formula 4.98) and glyoxal (IV,

Formula 4.98). The synthesis of GLARG is

displayed in Formula 4.99. It is interesting that

glyoxal reacts with the N-atoms 1 and 2 of

the guanidino group (Formula 4.99), whereas

methylglyoxal bridges N-2 and N-3.

Among the identified compounds, only ornithino-

imidazolinone (I, Formula 4.98) has been quanti-

Table 4.15.Concentrations of ornithino-imidazolinone

(OIZ) in foods

Foods OIZ Arginine loss

(mg/kg protein) (%)

Alkali-baked 9000–13, 000 20–30

products

Pretzel crust 25 ,000–28,000 60–70

Coffee beans 7000–9000 20–25

(roasted)

Nibbling 6000–20, 000 15–40

biscuits