Separation of caseinomacropeptide fromwhey by means of electrically enhanced cross-flow membrane filtration

摘要

The objective of this study was to investigate whether caseinomacropeptide (CMP) can be separated from the major whey proteins alpha-lactalbumin (alphalpha-La) and betalpha-lactoglobulin (betalpha-Lg) by means of electrically enhanced cross-flow membrane filtration (EMCF) using sweet whey as a model solution. Electro membrane filtration is a technique which combines separation by means of size exclusion and charge effects by superimposition of an electrical field upon conventional cross-flow membranefiltration. CMP has a strong acidic character (p/< 4.2) and thus a basically negative charge at pH 4.0, whereas the major whey proteins alpha-La (p/4.2-4.5) and betalpha-Lg (p/5.1) are positively charged. The electrode configuration of the EMCF module was specifically set to favour the permeation of negatively charged CMP on the permeate side (anode +) and increase the retention of positively charged alpha-La and betalpha-Lg on the retentate side (cathode -). EMCF improved the separation between CMP and the whey proteins alpha-La and betalpha-Lg in the model sweet whey solution at pH 4.0 compared to mierofiltration (0.1 urn) without electrical field. The retention of positively charged alpha-La and betalpha-Lg was generally increased with higher voltage and the highest separation factor was observed at 5 V. Electrolytic effects such as water splitting and gas formation occurred in the EMCF process. These reactions led to the production of hydroxide ions (OH~-) and hydrogen (H_2) at the cathode (retentate) side and hydronium ions (H_3O~-) and oxygen (O_2) at the anode (permeate) side. This resulted in a considerable acidification and increased conductivity of the permeate. The appearance of membrane discoloration, the effect of electrolytic reactions(water splitting, gas formation) on the proteins, and possible occurrence of protein denaturation has to be clarified. Nevertheless, electrically enhanced cross-flow membrane filtration shows great potential for separation of complex protein mixtures such as cheese whey or other charged molecules of interest from complex feed stocks.