[Fourier Transform Infrared spectroscopy (FTIR) as a screening method for freezing point in raw milk]

ABSTRACT The objective of this study was to investigate the interference of milk fat content upon the Freezing Point (FP) obtained by Fourier-transform infrared (FTIR). A fraction of raw milk was skimmed, obtaining cream and skim milk. Whole and skim milk were added with water (0, 2, 5, 10, 15, and 20%). The remaining skim milk was added with cream (5, 10, 15, 20%) and water (0, 2, 5, 10, 15, and 20%). Samples were analyzed for FP (thermistor cryoscope and FTIR) and composition (FTIR). FP measured by FTIR was highly correlated with the thermistor cryoscope method (above 98.5%) and, as expected, water addition was significant (P≤0.001) upon increasing milk FP in both methods. However, high fat content in raw milk resulted in decreasing FP when using FTIR, while low fat content resulted in increased FP (P≤0.001). Since water addition caused the inverse effect of high fat on FP measured by FTIR, it is important to regard the fat content of milk to avoid misinterpretation of FP when using the FTIR method.