The determination of residual lactose in lactose- reduced milk by Lactoscope FTIR advanced

This application note reports on the development of a calibration model, its validation and applicability for the determination of residual lactose in lactose-reduced milk and milk products using a Lactoscope FTIR Advanced (FTA) Instrument. The calibration model developed for milk was based on a set of 76 samples, including process samples, endproducts of various brands of skim milk, semi skim and whole milk and a single brand of cat milk and mixes with regular milk, milk protein retentate and milk permeate. A similar set (39 samples) was prepared for the validation study, half a year later. Accuracies, as determined from the standard error of cross validation (SECV) for the calibration and the standard error of prediction (SEP) for the validation, were 0.07%m/m and 0.04%m/m respectively. Repeatability standard deviation (SDrep) was typically better than 0.025%m/m. An additional model for cream was established by inclusion of a sub set of 7 cream samples. Mean results of determinations in 5-fold for 5 samples of whole milk and 11 samples of half cream milk of different production dates but of a single brand were used to demonstrate the applicability of the method for end-criteria control of lactose levels in process monitoring. For both products mean results were close to “zero” %m/m lactose and revealed a minimal variation among samples, characterized by a standard deviation in the mean results (SD(mean)) of 0.02 %m/m. Tests on cream yielded similar positive results. In contrast, tests with lactose reduced chocolate milks and 2 brands of different cat milks had higher variability. Measured values based on the model differed from declared contents by several % in m/m, and chocolate milk results were highly variable (by several % m/m). Causes are discussed and possibilities of corrections explained. Introduction “Lactose-reduced” milk and milk products, also referred to as “low lactose” or “lactose-free” milk products, are of special commercial interest since the lactose present in regular milk products make it unsuitable for the majority of the world's adult population [1]. This is referred to as “lactose intolerance”, i.e. the inability to cleave the disaccharide lactose into the monosaccharide’s glucose and galactose, by lactase in the small intestine. “Lactose-free” milk is mostly produced by treating milk with -galactosidase, typically the lactase from Kluyveromyces Lactis [2]. The progress of the enzymatic reaction depends primarily on temperature, enzyme concentration and reaction inhibition by the galactose formed. At high lactose and galactose concentrations moreover, lactase shows significant transferase ability and produces b1,6-linked galactosyl oligosaccharides. In industrial Figure 1