Comparison of casein glycations induced by lactose and lactulose

Effects of lactose and lactulose on the casein glycation process at different times and specific glycation sites were investigated. Lactulose treatment generated higher levels of initial glycation products fructoselysine (1.160 μg/mL) and methylglyoxal (0.266 mg/mL) than lactose treatment which had 0.959 μg/mL and 0.140 mg/mL, respectively. The concentrations of intermediate products Nε-(Carboxymethyl) lysine (0.654 μg/mL) and Nε-(Carboxyethyl) lysine (0.154 μg/mL) in the lactulose treatment were approximately 2.5 and 1.1 times higher than these in the lactose treatment, respectively. The glycation induced by lactulose targeted Lys residues and had more glycated peptide fragments and wide-ranging glycation sites in α_s1-casein. The high degree of casein glycation in lactulose treatment was attributed by the fructose on lactulose which had different pathways in the Maillard reaction, compared with the glucose on lactose. The findings revealed the differences of casein glycations by the two sugars and during thermal processing. The information could be helpful in developing potential approaches to monitor and control glycation reactions in dairy products.