Improved recovery of B-phycoerythrin produced by the red microalga Porphyridium cruentum

A simplified process for the primary recovery and purification of B-phycoerythrin (BPE) from Porphyridium cruentum exploiting aqueous two-phase systems (ATPS) and isoelectric precipitation was developed in order to reduce the number of unit operations and benefit from increased purity and yield of the protein product. Evaluation of the partitioning behaviour of BPE in polyethylene glycol (PEG)/sulphate, PEG/dextran and PEG/phosphate ATPS was carried out to determine under what conditions the BPE and contaminants concentrated into opposite phases. An additional stage of isoelectric precipitation at pH 4.0 after cell disruption resulted in an increase in purity of the target protein from the BPE crude extract and enhanced the performance of the subsequent ATPS. PEG1000/phosphate ATPS proved to be suitable after isoelectric precipitation for the recovery of highly purified (defined as absorbance ratio A545 (nm)/A(280 nm) > 4.0) BPE with a potential commercial value as high as US$50/mg. An ATPS extraction stage comprising 29.5% (w/w) PEG1000, 9.0% (w/w) phosphate, a volume ratio (V-r) equal to 1.0, a system pH of 7.0 and loaded with 40% (w/w) of the BPE extract generated by precipitation allowed BPE recovery with a purity of 4.1 +/- 0.2 and an overall product yield of 72% (w/w). The purity of BPE from the crude extract increased 5.9-fold after isoelectric precipitation and ATPS. The results reported herein demonstrate the benefits of the practical application of isoelectric precipitation together with ATPS for the recovery and purification of BPE produced by P. cruentum as a first step in the development of a commercial purification process. (c) 2006 Society of Chemical Industry.