Methods and compositions involving whey protein isolates

Abstract

The present invention concerns methods of isolating milk proteins. Methods of the invention include charged ultrafiltration processes that use variations in pH to further separate protein species.

What is claimed is: 
     
         1 . A method for fractionating a protein mixture, the method comprising:
 (a) adjusting the pH of the protein mixture based on an isoelectric point of a protein of interest in the protein mixture, thereby rendering a net charge of about zero on the protein of interest;   (b) adjusting conductivity of the protein mixture such that proteins other than the protein of interest are rejected by a charged ultrafiltration membrane; and   (c) contacting the mixture with a charged ultrafiltration membrane to achieve a first permeate and a first retentate, wherein the ultrafiltration membrane has a pore size at least 10× greater than the molecular mass of at least one of the proteins other than the protein of interest, and has a pore size of between about 86 kDa and about 1,600 kDa, wherein the first permeate comprises an increased ratio of the protein of interest as compared to the protein mixture.   
     
     
         2 . The method of  claim 1 , wherein the protein mixture is a milk protein or a whey protein mixture. 
     
     
         3 . The method of  claim 1 , further comprising subjecting the first permeate to a second charged ultrafiltration to achieve a second permeate and a second retentate. 
     
     
         4 . The method of  claim 3 , wherein the second retentate is recycled into another protein mixture for additional charged ultrafiltration. 
     
     
         5 . The method of  claim 3 , wherein the ultrafiltration achieves a purity of about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%. 
     
     
         6 . The method of  claim 3 , wherein the ultrafiltration achieves a yield of about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%. 
     
     
         7 . The method of  claim 1 , further comprising subjecting the first retentate to a second charged ultrafiltration to achieve a second retentate and a second permeate. 
     
     
         8 . The method of  claim 7 , wherein the second permeate is recycled into another protein mixture for additional charged ultrafiltration. 
     
     
         9 . The method of  claim 7 , wherein the ultrafiltration achieves a purity of about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%. 
     
     
         10 . The method of  claim 7 , wherein the ultrafiltration achieves a yield of about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%. 
     
     
         11 . The method of  claim 1 , wherein the ultrafiltration achieves a purity of about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%. 
     
     
         12 . The method of  claim 1 , wherein the ultrafiltration achieves a yield of about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%. 
     
     
         13 . The method of  claim 3 , wherein the ultrafiltration membrane is positively charged or negatively charged. 
     
     
         14 . The method of  claim 1 , wherein the conductivity is adjusted to 3-10 mS/cm. 
     
     
         15 . The method of  claim 1 , wherein GMP is separated from ALA, IgG, or BLG; or wherein ALA is separated from IgG or BLG; or wherein BLG is separated from IgG. 
     
     
         16 . The method of  claim 1 , wherein the charged ultrafiltration is effected by a multistage cross-flow positively charged ultrafiltration membrane.