Rapid method for determination of milk casein content by infrared analysis

Preliminary work was to develop a method for determination of milk casein content using commercially available infrared milk testing equipment. Fresh whole milk samples were split into two portions. One portion was tested for total protein with an infrared milk analyzer. The other portion was adjusted to pH 4.6 with a specific volume and concentration of phosphoric acid. Milk casein precipitated at pH 4.6 and was removed by filtration. Next, the noncasein protein filtrate was tested for protein content using an infrared milk analyzer. The difference between the percent protein of the original milk sample and the percent protein of the noncasein protein filtrate equals the percent milk casein. The infrared casein determination for 36 different individual herd milk samples was not significantly different from results obtained by the official International Dairy Federation casein testing method. The infrared method is faster than the chemical method and could be done with infrared milk testing equipment that is commonly available in many cheese manufacturing plants. Repeatability of the infrared method was comparable to the repeatability of the chemical method.