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) has been optimised 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 relative standard deviations for repeatability was 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 found (lower than 0.1%) in samples of milk, and yogurt declared as lactose-free, as well as in parmesan, cheddar, gouda and trappist cheese samples. In various dairy products measured lactose content was in range from 0.493±0.026% in home-made rolled cheese to 4.42±0.180% in cooking sour cream.