Green method using water for lactose and lactulose extraction and determination in milk by high-performance liquid chromatography with refractive index detection

Abstract Lactose is the main carbohydrate found in milk. However, the ultra-high temperature (UHT) process might convert lactose to lactulose by isomerization. Lactulose can be prebiotic; nevertheless, at high concentrations, it can be fermented in the gastrointestinal tract because it is not hydrolyzed by enzymes. In view of the increase in lactose intolerant consumers, it becomes necessary to determine the presence and amounts these compounds in UHT milk. Hence, this study aims to propose and validate a method with simple sample preparation to measure lactose and lactulose contents in milk. Following green chemistry principles, the proposed method is distinguished by the use of only water in the extraction step, with an effective sample clean-up step performed via ultracentrifugation; likewise, water was also employed as the mobile phase for high-performance liquid chromatography with refractive index detection analysis. Moreover, the proposed method allows for the verification of the efficiency of the lactose-free milk process by monitoring lactose residual levels in addition to measuring the degradation contents of glucose and galactose. Further, the developed method even represents an alternative for detecting counterfeit milk made with added sucrose, ensuring the quality of milk for consumers.