Evaluation of multiple purification strategies and characterization of R-phycoerythrin from two species of red seaweed, Furcellaria lumbricalis and Schizymenia valentinae

Abstract

R-phycoerythrin (R-PE) is a prospective natural red colorant present in red seaweed and consists of three major subunits α, β, and γ. This study aimed to investigate the outcome of intensity of R-PE subunits obtained from different purification strategies of the two red seaweed species, Furcellaria lumbricalis and Schizymenia valentinae comb. nov. R-PE was purified by i) multi-step ammonium sulphate precipitation, ii) membrane filtration, iii) anion exchange chromatography, and iv) a combination of multi-step ammonium sulphate precipitation followed by anion exchange chromatography. The characterization of purified R-PE was carried out by spectrophotometric analysis, SDS-PAGE, 3D fluorescence scan and mass spectrometry. The increased purity index and wider excitation and emission wavelengths reflected the improved purification of R-PE from both species of red seaweed relative to the crude extracts. The MS study identified peptides from other phycobiliproteins such as phycocyanin, allophycocyanin, and RuBisCO after membrane filtration. After membrane filtration, the α, β, γ subunits of R-PE, as well as phycocyanin, allophycocyanin, and RuBisCO displayed higher intensities in the purified R-PE from S. valentinae compared to F. lumbricalis, although the latter exhibited a more pronounced colour. The same was the case for samples purified by ammonium sulphate precipitation. The highest purity index was achieved after multi-step ammonium sulphate precipitation followed by anion exchange chromatography of R-PE from F. lumbricalis, which permits its utilization in food applications, although minor amounts of phycocyanin and allophycocyanin, were detected. In conclusion, separation of photosynthetic proteins was incomplete for all purification strategies.