Determination of protein and casein in milk by fourth derivative UV spectrophotometry Original Research Article

The aim was to develop a simple and rapid method for determination of milk protein in general, and casein content in particular, in milk without involving preparation procedures such as skimming and casein precipitation. Fresh raw milk samples were diluted with 6 M guanidine-HCl buffer before spectroscopic scanning. The total protein and casein contents of 45 milk samples determined by this method were not statistically significantly different from the values obtained by the reference method based on Kjeldahl determination of N (p < 0.05). By using fourth derivative UV spectrophotometers, the determination of total protein and casein content in milk can be achieved directly in a single run. Treatments of milk such as heating, homogenization, preservation or hydrolysis with protease had no influence on the accuracy of protein determination in milk by this method. The accuracy of determination with 0.03% total protein and 0.04% casein for the reference method could not be achieved under the condition used, due to the effect of high dilution rate.