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B. Lendl, A. Schwaighofer, M. Alcaraz, J. Kuligowski:
"Direct determination of casein, α-lactalbumin and β-lactoglobulin in cow´s milk using an external-cavity quantum cascade laser and chemometric data analysis";
Poster: FLAIR 2016, Aix-les-Bains; 12.09.2016 - 16.09.2016.

The determination of total protein content in cow´s milk is a routine application of mid-infrared (IR) transmission spectroscopy. However, the quantitation of protein in this kind of samples demands laborious and time consuming experimental work. We report an analytical method based on the direct spectroscopic determination of casein (Cas), α-lactalbumin (αLA) and β-lactoglobulin (βLG) in cow milk samples. For spectra acquisition, a custom-made setup equipped with a tunable EC-QCL light source, operated in pulsed mode at room temperature, and a temperature stabilized flow cell with an optical path length of 38 µm was used. An advanced data processing protocol was applied to compensate for fluctuations in the fine structure of the emission curve that are inherent to the employed light source due to mechanical instabilities [1]. Mid-IR transmission spectra of aqueous protein standard mixtures, as well as cow´s milk and spiked cow´s milk samples were acquired in the 1600-1700 cm-1 region (amide I band). Science based calibration (SBC) algorithm was employed for compensation of changes in the background signal attributed to the milk matrix. After background correction, partial least squares (PLS) was employed to build regression models for each of the three proteins by comprising spectra of aqueous calibration standard solutions and background-corrected milk samples. Finally, predictions of individual protein concentrations in commercial and spiked cow´s milk were carried out. Protein concentrations determined in commercially available milk samples were 24.5±1.4, 1.4±0.9 and 2.4±0.2 mg mL-1 for Cas, αLA and βLG, respectively. Recovery values for spiked samples were ranging between 95±8%, 101±22% and 99±4% for Cas, αLA and βLG, respectively. In light of the results obtained, this high throughout method has the potential to be employed as a standard tool for quality control of milk, without requiring any sample preparation.