Chemistry Reference
In-Depth Information
method by including a pre-treatment involving heating samples in 0.3 N
oxalic acid at 1008C for 1 h to convert Amadori products and 1,2-E inter-
mediates to HMF. Although the measurement of HMF in dairy products has
been criticized on the grounds of lack of specificity (Burton, 1984), it is a
cheap and relatively simple method for monitoring Maillard reactions and is
still widely in use (De Block et al., 2003). HPLC methods are now available
for the determination of free and 'bound' HMF in dairy products exploiting
the strong absorption of HMF at 280 nm (van Boekel and Rehman, 1987;
Morales et al., 1997).
7.7.5.
Fluorescence Spectroscopy
The generation of fluorescent products in Maillard reactions is well
described and fluorescence spectroscopy has been used to monitor the devel-
opment of Maillard reactions in dairy products (Morales et al., 1996; Lecl`re
and Birlouez-Aragon, 2001; Bosch et al., 2007). However, the limitation of
classical methods is that they cannot be applied to turbid systems such as
dairy products without a sample preparation step. More recently, the appli-
cation of front-face (surface) fluorescence spectroscopy to dairy products
offers potential as a rapid non-destructive means of assessing product quality
(Kulmyrzaev and Dufour, 2002; Birlouez-Aragon et al., 2004). The coupling
of chemometric methods with fluorescence spectroscopy has been reported to
determine accurately the levels of both lactulose and furosine in milk samples
(Kulmyrzaev and Dufour, 2002).
7.7.6.
e
-Pyrrole Lysine
The advanced Maillard reaction product,
"
-pyrrole lysine, has been
proposed as a useful indicator of reactions in stored foods because Amadori
products tend to decompose over time to other products, limiting their
usefulness as indicators of Maillard reactions (Chiang, 1988). Chiang (1988)
found that
"
-pyrrole lysine was readily detectable in skim milk powder heated
at 808C for 1 or 2 h (6.25 or 20.32 mg kg
-1
, respectively).
7.7.7.
Carboxymethyl Lysine
An alternative to the furosine assay is the measurement of
N-
"
-carboxymethyl lysine (CML; Figure 7.6) formed by oxidation of the
protein-bound Amadori product (Erbersdobler and Dehn-M ¨ ller, 1989;
Badoud et al., 1990; L ¨ demann and Erbersdobler, 1990). In the case of
milk products, the method involves the oxidation of lactulosyl lysine using
periodic acid, followed by acid hydrolysis. The method is reported to have the
