Using charged membranes to improve dairy protein ingredients
This research examines two hypotheses: (1) negatively charged ultrafiltration (UF) membranes can be used to manufacture whey protein and milk protein ingredients at enhanced flux, and (2) positively charged UF membranes can be used to make dairy protein fractions without the use of chromatography. Charged UF membranes are fabricated from normal uncharged UF membranes. The membrane charge combines with the membrane molecular weight cutoff to control whether or not proteins permeate or are retained by the membrane. At the neutral pH of milk and whey, the major proteins are charged negative and are rejected by a negatively charged UF membrane, allowing the use of wide pore size membranes that operate at high flux. Compared to current uncharged 10 kDa membranes, 100 to 300 kDa charged UF membranes have a 2-5X higher flux at the same or increased protein retention. We scaled up this technology 1400X from 50-1000 cm2 flat sheet systems to 70,000 cm2 spiral wound systems. In the fractionation of proteins from milk or whey, chromatographic purity can be obtained without the use of chromatography. For example, by attaching a positive charge to a 300 kDa UF membrane, selectivity increased by a factor of 3 for fractionating bovine alpha-lactalbumin from beta-lactoglobulin in milk-serum, compared to an unmodified membrane. Thus, like-sized proteins that differed only somewhat in isoelectric point and size, and that were about 15-20 times smaller than the membrane molecular weight cutoff were fractionated using charged UF membranes.
Keywords: proteins, membranes, processing