Various properties of individual or only some milk compounds may be required for an application or other compounds may have a detrimental effect, so special-purpose powders are increasingly being produced from part-components of milk instead of whole milk ingredients. The rapid development of microfiltration, ultrafiltration, nanofiltration and reverse osmosis membrane separation technologies is making it increasingly easy to break milk down into its separate constituents.
For example, powders produced for protein standardisation in cheesemaking have a high concentration of native casein. As the whey protein is not needed for cheese production, it is separated off and used for other specific purposes. During such separation membrane technology makes use of the size difference between casein micelles and milk proteins. Casein micelles are approx. 0.01 – 0.3 µm in diameter, whey proteins 0.003 – 0. 06 µm. The two proteins can be separated by the appropriate membrane in this separation range. The casein stays behind in the retentate, the whey proteins, lactose and minerals pass into the permeate. The additional use of dialysis – the addition of water to dilute the remaining substances – produces a purer form of casein in the retentate. Lactose and minerals can be separated from the permeate by an even finer membrane – ultrafiltration. Here again the additional use of dialysis can produce a purer form of whey protein. This process therefore delivers caseins and whey proteins in concentrated form. Gentle processing ensures that a large proportion of these proteins are in their native form with the corresponding functional properties, e.g. the renneting ability of caseins or the high water-binding properties of whey proteins.
Ultrafiltration is carried out only once for the production of total milk protein powders – if necessary coupled with dialysis for purification.
The products are preserved by spray drying following membrane separation and concentration.