Inspection of milk components by terahertz attenuated total reflectance (THz-ATR) spectrometer equipped temperature controller

It was confirmed that THz spectroscopy has a potential for quantitative analysis of milk fat, total solid, lactose, milk protein, casein and somatic cell. We investigated the correlation between the absorption spectrum of raw milk in the THz region and the measured milk contents by the Partial Least Square (PLS) regression and full cross validation as test for the calibration models. It was difficult to conduct transmission measurements because the absorption of water in the THz range is large. Thus, we used the attenuated total reflection (ATR) method with a high resistance silicon ATR-prism. This prism equipped a sample temperature controller to reduce the error due to temperature dependent changes of spectra. As the result of this experimentation, the R² of validation of the best regression model to predict milk fat, total solid, lactose, milk protein, casein and somatic cell were 0.72, 0.80, 0.38, 0.37, 0.41 and 0.67. It was inferred that THz spectroscopy is suitable to predict several milk contents such as milk fat, total solid and somatic cell counts.