A simple method for rapid purification of phycobiliproteins based on membrane chromatography

Phycobiliproteins are brilliantly coloured, highly fluorescent pigments of the photosynthetic light-harvesting antenna complexes of cyanobacteria and some algae, such as Rhodophyta and Cryptomonads. These water soluble bright blue (phycocyanin (PC) and allophycocyanin (APC)) and fuchsia (phycoerythrin (PE)) pigments are valuable products, with several commercial applications in pharmaceutics, cosmetics and foods. The commercial value of a phycobiliprotein is strongly dependent on its purity grade. For example, PC is largely used in food industry, being one of the very few natural, safe blue colorant available. The cost of PC as food colorant is relatively low, about US$ 0.35 per gram, because low purity is requested, but for cosmetic use it increases to about US$ 135, and for therapeutic and biomedicine applications, where a higher purity is required, PC cost can reach as much as US$ 4,500 per gram. Here we present a simple and rapid method to purify phycobiliproteins from cyanobacteria and microalgae based on membrane chromatography (MC) that is being patented by us. The MC process is performed using hydrophilic PVDF membranes, and inducing selective and reversible protein-membrane interactions by ammonium sulphate. Changing ammonium sulphate concentration it is possible to selectively separate the various phycobiliproteins present in the biomass extract, as well as to tune the procedure itself to obtain products of various purity grade, maximizing the yield.