The effect of lactose and its isomerization product lactulose on functional and structural properties of glycated casein

Lactulose is an isomer of lactose, formed under thermal processing of milk. Alkaline conditions favor the isomerization of lactose. As reducing sugar, lactose and lactulose could participate in the Maillard reaction and cause protein glycation in milk products. In this study, the influence of lactose and lactulose on the functional and structural properties of glycated casein was investigated. The results demonstrated that compared with lactose, lactulose led to severer changes in molecular weight, more disordered spatial structure and decrease of tryptophan fluorescence intensity of casein. Besides, the glycation degree and advanced glycation end products (AGEs) results suggested that lactulose exhibited stronger glycation ability than lactose due to the higher pro-portion of open chain in solution. Furthermore, higher glycation degree induced by lactulose resulted in lower solubility, surface hydrophobicity, digestibility and emulsifying capacity of casein-glycoconjugates compared with lactose. The results of this study are essential for tracking the effects of harmful Maillard reaction products on the quality of milk and dairy products.

Automated summary

This study investigated the influence of lactose and lactulose on the functional and structural properties of glycated casein. The results showed that lactulose led to more severe changes in molecular weight, spatial structure, and tryptophan fluorescence intensity of casein compared to lactose. Lactulose also exhibited stronger glycation ability, resulting in lower solubility, surface hydrophobicity, digestibility, and emulsifying capacity of casein-glycoconjugates compared to lactose. These findings are important for understanding the effects of harmful Maillard reaction products on milk and dairy product quality.