Comparison of IR and Raman spectroscopy methods for assessing structural changes in milk during heat treatment

Introduction: Quality control of dairy products requires fast, accurate, and simple analytical methods. Infrared spectroscopy, often using imported instruments, is widely used, necessitating the development of Russian equivalents and the search for alternative control methods. One such method is Raman spectroscopy, which offers advantages such as lower sensitivity to water contamination in samples, high information yield, and the ability to convert spectral metrics into quantitative data. In Russia, this method is rarely used for milk quality analysis, making research into its adaptation and comparative evaluation with traditional approaches crucial.

Purpose: A comparison of infrared and Raman spectroscopy in the analysis of skim pasteurized milk obtained under different temperature loads, and the determination of spectral ranges most sensitive to temperature for improving quality control methods for dairy products in Russian practice.

Materials and Methods: Spectra were recorded on samples of skim pasteurized milk heated to 70, 80, and 90°C and held for 30 seconds. Milk heated to 45°C served as a control. Russian equipment was used: an Infraspek-1201 infrared spectrometer and an RS-IK785 Raman spectrometer. The spectra were analyzed using principal component analysis.

Results: For the infrared spectra of the samples, changes were recorded in the regions of amides I-III (1640-1660 cm^-1, 1530-1550 cm^-1 and 1230-1300 cm^-1, respectively), lactose (1040-1150 cm^-1), lipid-protein complexes (2850-2950 cm^-1) and water (3200-3400 cm^-1). Visual differences in the spectral parameters were minimal visually and in terms of absorption (relative units). The principal component analysis allowed us to identify the contribution of the listed wavenumber ranges to the differences between the samples. Raman spectroscopy recorded pronounced differences in the zones of 280-520 cm^-1, 800-850 cm^-1, 1450 cm^-1, 1660 cm^-1 and 2850-2950 cm^-1, characterizing the main components of the dairy system. A clear trend of decreasing intensity of the characteristic bands with increasing processing temperature was revealed. Principal component analysis revealed the contribution of milk components (proteins, carbohydrates, and lipids) to the differences between the samples.

Conclusion: The obtained data demonstrate the higher sensitivity of Raman spectroscopy in detecting thermally induced transformations of milk components compared to infrared spectroscopy. The results confirm the potential of using the Russian Raman spectrometer for assessing the quality of dairy products.

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