Determining the Composition of Proteins in Milk Using a Portable near Infrared Spectrometer

The content ratio of whey proteins to casein can serve as an indicator of milk quality as well as criterion for the presence of milk proteins adulteration, if it exceeds 0.25. The actual task is to produce an effective and portable sensor for the named ratio. The applicability of an inexpensive portable near infrared spectrometer for the specified task was tested in this work. The streams of backscattering and transmission light in the samples of the restored milk were acquired in the form of optical density spectra for a wavelength range of 800–1065 nm using a new two-channel CCD spectrometer. It was calibrated on the content of fat, casein and whey proteins using partial least squares regression. Another objective was to develop a cost-effective way to obtain a set of reference samples with various concentrations of three components that are needed to create the calibration models or to test them. Testing the calibration designed for the measurement of fat, casein and whey proteins in drinking milk showed root mean squared errors of prediction of 0.09% wt, 0.12% wt and 0.06%wt, and correlation coefficients of 0.90, 0.82 and 0.89, respectively. The value of the 95th percentile for the ratio of whey proteins to casein was found to be±0.06, which is sufficiently low for practical use of the method. A comparison of models, one of which was built using the proposed “custom” set of 35 samples and the other which was based on a random set of 81 samples, showed similar acceptable results. Thus, the proposed method is suitable for cost reduction without loss of calibration quality.