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.

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 method based on quick, easy, cheap, effective, rugged, safe (QuEChERS) extraction combined with gas chromatography-tandem mass spectrometry (GC-MS/MS) for the simultaneous quantitative determination of 12 organophosphorus and carbamate pesticide residues in soy milk. The samples were extracted with acetonitrile, then the supernatant was separated after addition of citrate buffer, followed by cleanup with a mixture of anhydrous magnesium sulfate, primary secondary amine (PSA) and C18 sorbents. The analytes were detected by GC-MS/MS. The results showed that the limits of quantification (LOQs) were 0.004 mg/kg for the 12 pesticides. The calibration curves were linear in the concentration range of 5–200 ng/mL with correlation coefficient greater than 0.99. The recoveries varied from 71.8% to 114.9% with relative standard deviation (RSD) from 4.6% to 13.3% at three different spiked levels. The method was found to be quick, efficient, accurate and suitable for the determination of organophosphorus and carbamate pesticide residues in soy milk.

The detection of pesticide residues in dairy products is an important measure to ensure the quality and safety of dairy products. Currently, QuEChERS (quick, easy, cheap, effective, rugged, safe) is widely used as a sample pretreatment for all existing methods specified in the national standards for the detection of pesticide residues in dairy products. In this paper, we review these methods with a special focus on the principle and advantages of QuEChERS as well as its application in the detection of pesticide residues in dairy products.

This paper summarizes and compares the maximum residue limits for pyrethroid pesticides in milk products in China and several other countries. At the same time, the main factors affecting the accuracy of the determination of pyrethroid pesticide residues in dairy products, including calibration curve fitting and experimental repeatability, are determined through calculation of the measurement uncertainty. Furthermore, it can be argued that the most fundamental influencing factor is the sample pretreatment method.