Membrane Unit Operations for Dairy Protein Concentration and Fractionation.

摘要

The unique functional properties of different whey proteins and increasing use of these purified proteins as ingredients in food formulations have motivated researchers to develop new methods of purification. Ultrafiltration has been in use for years in the dairy industry mainly to concentrate whey to obtain whey protein concentrate and to produce whey protein isolate by further desalting or diafiltration of the concentrate. However, ultrafiltration is not able to fractionate individual proteins from whey. That is because current ultrafiltration membranes separate proteins based on differences in size only. The size difference between the whey proteins is not large enough to fractionate the proteins. The overall objective of the present research was to develop charged ultrafiltration membranes for the fractionation of whey proteins. The premise of the research is that although the different whey proteins do not differ greatly in molecular weight, the isoelectric points are markedly different. This allows the membrane charge and protein charge to be carefully controlled to increase the selectivity of the fractionation. Furthermore, use of multistage configurations with recycling of the selected streams increases the purity and the recovery of the desired protein. In this study, uncharged and positively charged cross-flow ultrafiltration membranes having a 300 or 30 kDa molecular weight cut-off were used in one, two and three stage configurations to fractionate glycomacropeptide (GMP) from other whey proteins. Sieving coefficients (permeability of the membrane to the protein), concentrations, purities and recoveries of the proteins were experimentally determined. Using sieving coefficients of the proteins in two different mass balance models, concentrations, purities and recoveries of the proteins were calculated and compared with the experimental results. In conclusion, using positively charged membranes in stage configurations was successful in fractionation of GMP. Purity and recovery were altered using different flow configurations and membranes having different molecular weight cut offs. Calculations obtained from two mass balance models were in close agreement with the experimental results. These mass balance models can be used to design different ultrafiltration systems with different stage configurations.