Dual-gating pH-responsive membranes with the heterogeneous structure for whey protein fractionation

Whey protein is a mixture of globular proteins with high nutritional value and excellent functional properties availability. Purified individual whey proteins exhibit better functionality than in their original mixture, thus there is an increasing interest in developing more efficient methods to recover individual whey protein fractions, especially membrane technology. However, whey protein fractionation from the protein mixture is still a huge challenge for membrane separation. Herein, a dual-gating pHresponsive membrane with the heterogeneous structure was developed for whey protein fractionation. The heterogeneous structure of the membranes was obtained by grafting the dimethylaminoethyl methacrylate (DMAEMA) and 4-vinylpyridine (4VP) near the topside and inside the pores of the ethylene vinyl alcohol copolymer (EVAL) membranes based on selective modification of grafting sites. The PDMAEMA and P4VP gates responded to pH individually and provided a multi-stage regulation of the surface charge and sieving property of the membranes. The major whey protein fractionation from the mixture could be achieved by single dual-gating pH-responsive membrane via the sequential stepwise pH gradient from 3.0 to 8.0. The α-Lactalbumin (α-La), β-Lactoglobulin (β-Lg), lactoferrin (LF) and bovine serum albumin (BSA) were separated and enriched in the permeate at pH 3.0, 4.2, 6.4 and 8.0 by the diafiltration process, respectively. This work not only proposed a novel concept of pHresponsive membrane, but also offered a sustainable solution to fractionate the whey protein from the complicated mixture.