Abstract: In this study, we established a quantitative method for the detection of casein in dairy products using 31P nuclear magnetic resonance (NMR) combined with the interpolation method. The results showed that the limit of detection (LOD) of this method was 0.38 g/L (RSN = 3), and the limit of quantitation (LOQ) was 1.25 g/L (RSN = 10). Good linearity was observed within the concentration range of 5.00–35.00 g/L, with correlation coefficient R2 greater than 0.999. The spiked recoveries were in the range of 91.94%–105.10%. The intra-day and inter-day precisions (relative standard deviation, RSD) were in the range of 0.65%–1.40% and 1.40%–1.80%, respectively. The casein contents of different dairy products on the market were detected by this method and the current national standard method (GB 31638-?2016). The error between the two methods was within ± 5%, which met the requirements for comparative analysis and validation of feasibility. Compared with the conventional method, this method had the advantages of simpler sample pretreatment, higher quantitative accuracy, greatly shorter detection time and wider applicability. Therefore, it could be suitable for rapid determination of casein content in dairy products.

Key words: 31P nuclear magnetic resonance; interpolation method; quantitation; casein; dairy products