Lactose hydrolysis and protein fortification pose an increased risk for the formation of Maillard reaction products in UHT treated milk products

This study aimed to survey the content of Maillard reaction products in different UHT-treated milk products and to assess how formation of these products and lysine blockage is affected by the composition. For this purpose, different commercial UHT milks including milk (whole, semi-skimmed and skimmed), lactose-hydrolyzed, protein-fortified, lactose-hydrolyzed protein fortified and follow-on infant milks were analyzed. Among the Maillard reaction products, dicarbonyl compounds, 5-hydroxymethylfurfural, furosine, N-ε-carboxymethyllysine and N-ε-carboxyethyllysine were monitored. The results showed that fortification of UHT milks with protein and carbohydrates as well as hydrolysis of lactose promoted the Maillard reaction. Among the dicarbonyl compounds, 3-deoxyglucosone formation, which was the dominant dicarbonyl compound in milks, varied between 3.12–12.67 mg/L, 13.45–21.98 mg/L and 4.59–40.38 mg/L in lactose hydrolyzed, lactose-hydrolyzed protein-fortified and follow-on infant milks whereas it was 0.22-0.40 mg/L in milks, respectively. Similarly, 5-hydroxymethylfurfural could not be detected in milks, whereas mean 5-hydroxymethylfurfural concentration was found to be 56.3 mg/L and 31.5 mg/L in protein-fortified milks and lactose-hydrolyzed protein-fortified milks, respectively. Accordingly, % blocked lysine, furosine, N-ε-carboxymethyllysine and N-ε-carboxyethyllysine content of different UHT milks were found to be significantly higher than milks (p < 0.05). This is the first study reporting the Maillard reaction products in protein-fortified and infant milks.