Research in the field of membrane separation goes back to decades at the Hungarian Dairy Research Institute Ltd. (HDRI). Currently, one of the main areas of research is the fractionation, isolation and enrichment of milk-forming parts using different filtration technologies. The focus of research in this direction is the so-called cold microfiltration process, which has been less common in the industry so far.
To produce micellar casein (MCN), protein fractionation microfiltration is used in the dairy industry, during which the aim is to change the ratio of casein protein to whey protein in milk, from the original 80:20 to typically 95:5. During the process, the skimmed milk is filtered using 0.1-0.5 micrometers pore size membranes, applying pressure, traditionally at a filtration temperature of 40-45 °C. In contrast, during the less common cold microfiltration process, the filtration is carried out at 4-15 °C.
The advantage of cold microfiltration compared to the traditional warm microfiltration process is that due to the lower temperature, microbiological reproduction is smaller, so a longer operating time can be achieved. This reduces the relative washing time, so less chemicals are required. The disadvantage of the cold microfiltration process is that the viscosity of milk increases as the temperature decreases, so the filter capacity (flux) of the membranes decreases, thus more membrane surface is required to achieve the desired capacity.
Both hot and cold microfiltration result in a casein-rich retentate and a whey-protein-rich permeate. During our own research, however, we established that, with the same technological parameters applied, changing the filtration temperature affects the retention of the main whey protein fractions – α-lactalbumin, β-lactoglobulin A, β-lactoglobulin B proteins – in milk, thus the protein profile of the final products, as well as the development of the casein-whey protein ratio.
International research also reported that at a filtration temperature of 4 °C, β-casein (one of the fractions that make up the casein micelle) splits off from the micelle, which thus passes into the permeate. The permeate rich in the β-casein fraction can serve as an excellent raw material, for example, to produce breast-milk substitutes and breast milk supplements.
Henrietta Buzas
research fellow
