EXPRESS: Prediction of α-Lactalbumin and β-Lactoglobulin Composition of Aqueous Whey Solutions Using Fourier Transform Mid-Infrared and Near-Infrared Spectroscopy.

Characterization and quantification of individual whey proteins is crucial in many industrial dairy processes. With labor-intensive wet-chemical methods still being used as reference, a rapid quantification method for individual whey proteins is yet to be established. In this work Fourier Transform Mid-Infrared (FT-MIR) spectroscopy and Fourier Transform Near-Infrared (FT-NIR) spectroscopy were investigated as rapid methods for the analysis of the two main whey proteins (I²-lactoglobulin and I±-lactalbumin) in complex aqueous whey solutions simulating production process streams. MIR and NIR spectra were obtained on whey samples with known and varying amounts of the proteins of interest and regressed onto the spectra using Partial Least Squares (PLS). Selecting wavelengths allowed for prediction of I²-lactoglobulin and I±-lactalbumin concentrations with very high precision and accuracy (RMSECV of 0.6% and R2 of 0.99), suggesting the possibility of implementing systematic rapid in-line monitoring of protein composition in industrial whey streams. While the protein secondary structure fingerprint in the MIR region is well established in literature, this paper goes a step further by identifying the most informative parts of the NIR spectra in relation to protein secondary structure analysis through application of two-dimensional MIR-NIR correlation spectroscopy. Multivariate Curve Resolution (MCR) was applied to the MIR data to resolve mixture spectra and to elucidate the spectral ranges that were most useful in distinguishing between the two main whey proteins. The study concludes that NIR spectroscopy is a potential technology for accurate protein structural quantification, and that the method proposed here opens the possibilities for novel in-line industrial applications.