Determination of Some Adulterants in Milk Based on Two-dimensional Correlation-Near Infared Spectroscopy Analysis

Two-dimensional (2D) correlation near infrared (NIR) spectroscopic analysis was applied to the rapid determination of 3 adulterants (urea, glucose and melamine) in milk samples. The adulterants in different concentration ranges (i.e. 1-20 g·L-1 of urea, 1-20 g·L-1 of glucose and 0.01-3 g·L-1 of melamine) were added into 3 sets of milk samples separately (40 samples in each set) and the NIR spectra of the samples were measured. Then 2D correlation analysis was performed under the perturbation of concentration of these adulterants to study the characteristic peaks of the adulterants. 2 strong autocorrelation peaks located at 4 500 cm-1 and 4 648 cm-1, 3 strong autocorrelation peaks located at 4 456 cm-1, 4 392 cm-1 and 4 360 cm-1 and 2 strong autocorrelation peaks located at 4 256 cm-1 and 4 328 cm-1 were observed in the synchronous correlation spectra of milk samples adulterated by urea, glucose and melamine, respectively. All these peaks were exactly the characteristic absorption of the respective adulterants in milk. It was shown that correct recognition of the 3 adulterants in milk can be realized by the proposed 2D-correlation NIRS analysis, and it provides an alternative way for rapid discrimination of milk safety.