Chemistry Reference
In-Depth Information
illustrated by the work of Oste et al. (1990) who showed a decrease in the
antigenicity of Kunitz soybean trypsin inhibitor which had been heated with
glucose, lactose or maltose.
Recent research on the allergenicity of the major peanut allergens has
corroborated the above findings and has suggested a mechanism of action
that involved both increased IgE binding and a fourfold increase in trypsin
inhibitory activity (Maleki and Hurlburt, 2004), which would potentially
allow intact antigens to reach the systemic circulation. As Maillard reactions
have the potential to produce trypsin inhibitory compounds and to modify
the structure of food proteins, this area is in need of further research. Mean-
while, the effect of processing on a number of allergens has been studied
(Berrens, 1996; Wolff et al., 2004).
Research on the lactosylation of milk proteins during heating or storage
may help define the structural changes that influence milk protein allergeni-
city. Electrospray ionization MS and capillary electrophoresis have been used
to study the non-enzymatic glycosylation of milk proteins (Leonil et al., 1997;
Siciliano et al., 2000; French et al., 2002). Jones et al. (1998) demonstrated
that capillary electrophoresis can be used to monitor several glycated forms of
-lactoglobulin in skimmed milk powder. Guyomarc'h et al. (2000) were able
to show several new peaks for
-lactoglobulin,
-lactoglobulin,
s1
-casein,
-casein and
-casein, in capillary electropherograms. Additional analysis by
mass spectrometry suggested the increases in mass for the whey protein peaks
were approximately multiples of 320 Da consistent with incremental lactosy-
lation reactions. Other studies have demonstrated that lactosylation of
-lactoglobulin can proceed under relatively mild conditions in the absence
of browning is site specific (appearing to prefer Lys
47
), and results in con-
formational changes and ultimately aggregation via non-covalent interac-
tions (Leonil et al., 1997; Morgan et al., 1999b; Chevalier et al., 2002; French
et al., 2002; Czerwenka et al., 2006).
7.8.3.
Changes in Functional Properties
In both food systems and biological systems in vivo, there is evidence
that Maillard reactions may result in substantial changes in the functional
properties of proteins. Such changes include reduced enzyme activity, altered
receptor binding (Amaya et al., 1976), altered drug binding to plasma pro-
teins (Tsuchiya et al., 1984) and changes in protein stability (Kato et al.,
1983). Kato et al. (1981b,c) reported that Maillard reaction products of
ovalbumin and glucose were more soluble and heat stable than the native
protein. Electrophoretic studies confirmed that such protein-glucose adducts
had fewer positive charges. Circular dichroism spectroscopy revealed a more
ordered structure in the reacted protein than expected: even though 62% of
