Non-Enzymatic Degradation Pathways of Lactose and Their Significance in Dairy Products - Advanced Dairy Chemistry - page 266

advantage that the same oxidation product is formed regardless of the nature
of the sugar moiety of the Amadori product. In addition, the method can be
extended to the oxidation products of the Amadori products of several other
amino acids in addition to lysine; fluorescent detection of carboxymethyl
amino acids following HPLC separation affords high sensitivity (Badoud
et al., 1990). CML is also formed from fructosyl lysine and lactulosyl lysine
in food systems by the action of oxygen on the Amadori product. Its forma-
tion is promoted at low a w values, at high pH and by replacing glucose by
maltose or lactose in the food system (L ¨ demann and Erbersdobler, 1990).
L ¨ demann and Erbersdobler (1990) proposed that since CML is more heat
resistant than fructosyl lysine, its formation in foods could be a useful
indicator of advanced heat damage.

7.7.8. Pyrraline

The determination of the pyrrolealdehyde crosslink, pyrraline, may be a
useful marker of heat treatment in that it is independent of the degradation of
lactulosyl lysine and increases linearly with heating time of milk powder
samples (Henle et al., 1994). However, a dramatic decrease in pyrraline is
observed on prolonged heating (100-1108C for > 6 h). Levels of pyrraline in
food samples varied dramatically. Whereas levels in raw, pasteurized and
UHT milks did not exceed 2 mg kg -1 protein, levels in skim milk powder and
whey powder were as high as 1150 and 3150 mg kg -1 protein, respectively.
Concentrations in sterilized ( < 2-260 mg kg -1 protein) and evaporated
(110-130 mg kg -1 protein) milks appeared to be intermediate. In addition to
pyrraline, the authors also identified low levels of maltosine ( 30-fold less
than pyrraline) in samples of severely heated milk powder. It is assumed that
maltosine is formed via the 2,3-E pathway while pyrraline is a product of the
1,2-E pathway.

7.7.9. Immunoassays

The use of immunoassays to detect advanced Maillard products has
been the subject of several studies. However, a possible disadvantage of most
of these assays is that the antigens have not been subjected to full chemical
characterization. Kato et al. (1994) used monoclonal antibodies for a lactose-
protein Maillard reaction product to characterize a number of milk samples.
Skim milk powders showed reactivity to the antibody in all milk protein
fractions except the -casein fraction. Lactoferrin, serum albumin and the
immunoglobulins were only weakly reactive in the assay whereas s1 -casein,
-casein, -lactoglobulin and -lactalbumin were highly reactive. Packaging
of the skim milk powder in N 2 appeared to reduce the formation of the