Development of calibration with sample cell compensation for determining the fat content of unhomogenised raw milk by a simple near infrared transmittance method

A simple near infrared (NIR) transmittance measuring method for unhomogenised raw milk was developed using test tubes as sample cells and a specially designed sample holder which could control sample temperature. Short-wave NIR spectra (700-1100 nm) of 154 unhomogenised milk samples from eight cows, under different nutritional conditions, were measured at 40 degrees C using this method. The calibration and validation for fat content in raw milk were performed by partial least squares regression in two ways, using either a specific test tube or any individual test tube as a sample cell. A functional calibration model for determining fat content in raw milk with relatively high accuracy (multiple correlation coefficient of 0.99 and SEP of 0.19%) was obtained, which is applicable even when using individual test tubes as sample cells. By examining the loading weight of each factor included in the calibration model for fat determination in milk, it was found that the model consisted of, not only the factor for fat, but also factors which worked as adjusting terms, eliminating any effects caused by the other major components of milk such as lactose, casein and water and by the sample cell.