Determination of lactose in milk and dairy products by HPLC-RID method

Abstract

Fast, simple high-performance liquid chromatography (HPLC) method with refractive index detection (RID) was optimized and validated for the quantification of lactose in milk and dairy products. The method showed good linearity with determination coefficient 0.9975. The limit of detection was 0.04 mg/mL, and the limit of quantification 0.12 mg/mL. The relative standard deviations for repeatability were 4.00 and for reproducibility 4.98 in reference material, while in different tested matrix the relative standard deviations for repeatability were in range 2.58‒6.51. Average efficiency value was 97%. The applicability of the method was confirmed by its application in different samples. The presence of this sugar was not detected (lower than 0.1%) in the samples of milk and yogurt labelled as lactose-free, as well as in parmesan, cheddar, gouda and trappist cheese samples. In various dairy products the measured lactose content had values from 0.493±0.026% in home-made rolled cheese to 4.42±0.180% in cooking sour cream.