Design Considerations for the Batch Capture of Proteins from Raw Whole Milk by Ion Exchange Chromatography
Batch extraction of proteins directly from raw, whole milk is described with a focus on design considerations for on-farm implementation. A demonstration of single-stage stirred tank extraction of bovine lactoferrin onto cation exchangers shows that processing can be achieved, with no pre-treatment of raw milk, within the timeframe required to milk an individual animal. The extraction rates of two cation exchange media, SP Sepharose Big Beads™ and SP Sepharose FF™ (GE Healthcare, Uppsala, Sweden), are compared, with the smaller FF media (average diameter 90 μm) having a faster adsorption rate than the larger BB media (155 μm). Maximum percentages of original protein extracted by SP Sepharose FF were 67%, 80%, 88% and 90% for extraction times of 5, 10, 20 and 30 minutes, respectively. The composite nonlinear kinetic model of Rowe et al  was found to fit the batch adsorption of LF from raw milk as a function of chromatography media volume to milk volume ratio, Φ. At extraction times of 30 minutes and longer, extraction % was almost independent of Φ over the range of values tested. On-farm extraction of proteins shows promise for both the production of minor, high-value proteins from conventional milk and for production of recombinant proteins from the milk of transgenic animals. The main advantage of the stirred tank process is that protein extraction is rapid and is achieved in a single step without the need for pre-treatment of milk. The process is not limited to ion exchange but could be implemented using other chromatographic techniques, such as affinity or reverse-phase chromatography.