A simple and rapid ReMALDI MS assay for the determination of lactose in milk

Lactose is an important nutrient but its content in milk products poses concerns for people with lactose intolerance. Thus, a simple, rapid, and high-throughput assay for lactose determination is needed to maintain specified lactose levels during production and in final milk products. Here, we report a reactive matrix-assisted laser desorption/ionization mass spectrometry (ReMALDI MS) method for the determination of lactose in milk products. The selective reactivity and the excellent laser absorption properties of 4-hydrazinoquinazoline (4-HQ) matrix increase the sensitivity of traditional MALDI MS analysis of lactose by 100 folds. After optimization of the method, lactose was detected distinctly in milk without pretreatment. Using xylobiose as an internal standard, the assay accurately quantified lactose in the concentration range of 1.00-700 mu g/mL (R2 = 0.994). Due to the high sensitivity and specificity, the lactose content in different types of milk samples was determined successfully, as well as the residual lactose in low-lactose and lactose-free milk.