The development of electro-membrane filtration for the isolation of bioactive peptides: the effect of membrane selection and operating parameters on the transport rate

The ability to produce functional food ingredients from natural sources becomes increasingly attractive to the food industry. Antimicrobial (bioactive) ingredients, like peptides and proteins, can be isolated from hydrolysates with membrane filtration and/or chromatography. Electro-membrane filtration (EMF) is an alternative for the isolation of these usually strongly charged components. It is believed to be more selective than membrane filtration and less costly than chromatography. The isolation of bioactive peptides from a hydrolysate of αs2-casein, a protein originating from milk, was studied as a model separation for the development of EMF. This separation can be used as an example application for the isolation of other charged components from complex feedstocks in sseveral industries. After 4 h EMF the product consisted for 100% of proven or anticipated charged bioactive components. Diffusion and convection were negligible in relation to electrophoretic transport, since only charged components were recovered in the permeate product. The most important peptide (26% on total protein, starting from 7.5% in the feed) was αs2-casein ƒ(183–207), a very potent peptide against Gram positive and Gram negative microorganisms. The transport rate of αs2-casein ƒ(183–207) was reduced strongly when a polysulphone membrane with a molecular weight cut-off below 20 kDa was used. The amount of αs2-casein ƒ(183–207) transported increased practically linearly with the concentration and the applied potential difference. The use of desalinated feeds to further increase the electrical field strength in the feed compartment resulted in higher transport rates, but this increase was lower than expected probably due to the lower electrophoretic mobility. An average transport rate of 2.5 and 4 g/m2.h at maximum was achieved during 4 h EMF using GR60PP (25 kDa) and GR41PP (100 kDa) membranes respectively.