ATR-FTIR spectroscopy for in-line anomer concentration measurements in solution: A case study of lactose

Crystalline lactose is used in a variety of food and pharmaceutical products, and its crystallization is an important process in the dairy industry. However, the dynamics of lactose crystallization are complicated and, therefore, hard to predict. One reason for this is the mutarotation of lactose molecules, and, currently, there is no in-line technique for the measurement of mutarotation. Herein, we report on attenuated total reflection Fourier-transform infrared spectroscopy, a powerful in-line tool that simultaneously measures both total lactose concentration and the concentration of one of its anomers, α-lactose. Applying this method in a lab-scale crystallization reactor, we use it to measure the mutarotation kinetics of lactose over a wide range of temperatures and pH values to demonstrate its applicability for the crystallization of lactose based on process analytical technology.