Spectroscopic Measurement of Denatured Protein in Milk Products

The goal of this work is to create an Association of Official Analytical Chemists (AOAC) method to measure milk protein denaturation by Fourier-Transform Infrared spectroscopy (FT-IR). IR was chosen because it is relatively inexpensive, easy to use, and provides powerful analysis capabilities applicable to food and dairy processors. IR spectrometers are also an analytical instrument already commonly found in dairy processing laboratories. Milk has a protein content of 3.2-3.8%, which can be distinguished between whey and casein proteins. The various proteins in milk will be analyzed individually and in combination using both IR and circular dichroism spectroscopy (CD). IR will be used to measure the carbonyl absorbance present in the peptide bonds, and can provide characteristic absorbance signatures for folded versus unfolded proteins. CD will be used to monitor protein unfolding to validate the IR results. Protein denaturation is desirable in milk-based products, such as yogurt and cheese, however, denatured proteins also contribute to off-flavors and compromise milk quality in other products. A fast, economical, and easily implemented IR method for determination of milk protein denaturation will benefit the dairy industry by ensuring quality control and food safety