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.

Abnormal analysis of trace elements and heavy metal over-standard in dairy products are major concerns in the dairy industry, and how to detect elements of concern in dairy products quickly and accurately has become the focus of attention. Detection of elements in milk and dairy products is a prerequisite to ensure product quality and safety. Therefore, the pretreatment and detection methods specified in the Chinese and international standards for elements in milk and dairy products are reviewed. The principle, pros and cons of each method are elaborated so as to provide a reference for the detection of elements in the dairy industry.

A method for the determination of stevioside, rebaudioside A, rebaudioside B, rebaudioside C, rebaudioside F, dulcoside A, rubusoside and steviolbioside in fermented milk by high performance liquid chromatography (HPLC) was developed and validated. The chromatographic conditions and sample pretreatment conditions were optimized. Samples were ultrasonically extracted with water for 20 min and for another 10 min after addition of 30% acetonitrile in water bath at 45 ℃. Potassium ferrocyanide and zinc acetate were added to precipitate proteins. The chromatographic separation was achieved on a C18 with gradient elution using a mobile phase consisting of sodium phosphate buffer and acetonitrile, and the analytes were detected by an ultraviolet (UV) detector at 210 nm. The results showed that the method was linear in the concentration range of 1–50 μg/mL, the limit of detection (LOD, RS/N = 3) was 3.0 mg/kg, and the limit of quantitation (LOQ, RS/N = 10) was 10.0 mg/kg. The average recoveries of all analytes spiked at 15–200 mg/kg were between 92.0% and 103.1%, with relative standard deviation (RSDs) (n = 6) less than 3.0%. This method was rapid, accurate, stable, sensitive, and suitable for the analysis of the content of steviol glycosides in fermented milk.

A high performance liquid chromatographic (HPLC) method was developed for the determination of naringin in milk and dairy products. Samples were extracted with methanol, and the analytes were separated on a C18 column using a mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile (75:25, V/V), detected by a diode array detector at 284 nm and quantified by an external standard method. The results showed that the linearity of this method was good in the concentration range of 5–500 μg/mL with a correlation coefficient of 0.999 9. The recoveries of powdered and liquid milk power and yogurt spiked at 0.02, 0.04, and 0.08 g/100 g were 96.2%–103.2%, 96.3%–103.7%, and 99.7%–104.1%, respectively, with relative standard deviations (n = 6) of 1.12%–2.31%, 1.25%–1.85%, and 1.24%–1.66%, respectively. The reported method is simple, rapid, accurate, repeatable, and suitable for the determination of naringin in milk and dairy products.

Iodine is an important index of the nutritional quality of milk. Milk and dairy products are important dietary sources of iodine for humans, which has always aroused extensive concern. With the continuous exploration of nutrients in foods, research on iodine in milk has been increasingly intensified and refined. This paper reviews the recent literature on the factors that affects the iodine content of milk and the analytical methods that have been applied to determine it, which is expected to provide a reference for researchers in this industry and also provide a theoretical basis for the labelling of iodine in infant formula preparation.

In order to develop a new method to determine nitrite and nitrate in milk and milk products, some improvements were made on the ion chromatography method specified in the national standard GB 5009.33-2016 Determination of Nitrite and Nitrate in Food. Samples were extracted with ultra-pure water and added with acetic acid to precipitate proteins before being chromatographed on AS11-HC column and detected with a conductivity detector. Under the above conditions, the calibration curves for nitrite and nitrate were linear with correlation coefficients greater than 0.99. The limit of quantitation (LOQ) for nitrite and nitrate was 0.25 and 0.8 mg/kg in milk, and 1 and 5 mg/kg in milk powder, respectively. The recoveries for spiked samples of milk powder and milk were from 80% to 110%. The improved method was simple to operate and cheap with ideal recovery and high precision. It could avoid potential problems encountered in the use of the traditional method and allow for more rapid and accurate detection of low contents of nitrite and nitrate in milk and milk products.