Analysis of carboxymethyllysine (CML),
carboxyethyllysine (CEL) and furosine
The acid hydrolysis for the CML and CEL release from
the protein material and furosine conversion from
fructosyl-lysine residues present on the protein material
was performed based on the methodology described by
Buser et al. [24]. To a test tube with a screw cap with
PTFE coating was rigorously weighed 75 mg of freezedried
material. To each sample was added 3 mL of 7.8 M
HCl, and the resulting suspension was sonicated for
15 min in an ultrasound bath. The tubes were sealed under
nitrogen atmosphere, and the hydrolysis took place during
24 h at 110 C using a heating block. After cooling to
room temperature, the tubes content was evaporated to
dryness under vacuum. The resulting material was dissolved
in 4 mL of 2 M HCl and filtered with 0.45 lm
pore filters