A high performance liquid chromatography (HPLC) method for the detection of immunoglobulin G (IgG) in milk powder was established by studying the effects of immunoaffinity column performance, temperature of the sample solution during immunoaffinity column cleanup, and the type of eluent on the detection of the IgG content in milk powder. Samples were extracted with phosphate buffer solution, and the extract was purified by immunoaffinity column chromatography. The eluate was separated on a C₄ reversed-phase column (250 mm × 4.6 mm, 3.5 μm), detected using HPLC-ultraviolet detector, and quantified by an external standard method. The results showed that the method was applicable to milk powder with different IgG contents. The standard curve exhibited good linearity in the concentration range of 10-500 μg/mL. The detection limit of the method was 80 mg/kg, and the quantification limit was 300 mg/kg. The recoveries and precision expressed as relative standard deviations (RSDs) at three spiked levels (300, 600 and 3000 mg/kg) were both aligned with the requirements of the Chinese national food safety standard GB 5009.295-2023. This method is simple, efficient and accurate, providing precise technical support for the evaluation of the nutritional value of new functional dairy products and product claims.

In order to evaluate the influence of season on the fatty acid content of Holstein cow milk in Inner Mongolia, milk samples were collected from 10 large commercial pastures in Inner Mongolia during four seasons (spring, summer, autumn and winter) and analyzed for fatty acid content by gas chromatography (GC). The results showed that: 1) the major fatty acids in Holstein cow milk from Inner Mongolia were palmitic acid, oleic acid, stearic acid, myristic acid and linoleic acid, which did not change due to geographical regions, cow breeds, feeds and processing methods; 2) the proportions of saturated, monounsaturated and polyunsaturated fatty acids in the total fatty acids in cow milk were stable, and so were shortchain, medium-chain and long-chain fatty acids, which was not significantly affected by geographical regions; 3) the major fatty acids in cow milk presented the same trend with season, being at higher levels in spring and at lower levels in summer and autumn; 4) the contents of saturated and polyunsaturated fatty acids differed significantly (P < 0.05) between summer and the other seasons and were lowest in summer, and the content of monounsaturated fatty acids differed significantly (P < 0.05) between spring and summer and were also lowest in summer; and 5) the contents of short-chain and mediumchain fatty acids which have a strong influence on the flavor of milk fat differed significantly (P < 0.05) in summer and autumn compared to the other seasons. This study may provide reliable technical support for product innovation in the dairy industry and the improvement of milk nutritional value.

The proteases in cow’s milk have a great influence on the flavor and quality, especially on the shelf life of dairy products, but there is no uniform reference standard for the detection of protease activity in dairy products. This paper elaborates the sources, types and characteristics of protease in cow’s milk, and summarizes recent progress in the detection of the activity of different types of protease in cow’s milk, pointing out that the precise detection of protease activity in milk has great significance for dairy production and quality assurance.