Effect of high hydrostatic pressure on the structure of the soluble protein fraction in Porphyridium cruentum extracts

High hydrostatic pressure (HHP) treatments are trending as ``green'' stabilization and extraction process. The extraction of B-phycoerythrin from microalgae is getting more and more interest due to its numerous potentialities in foods, cosmetics and medicine. Thus, the effects of high pressure on the structural characteristics of B-phycoerythrin extracted from Porphyridium cruentum are explored in this paper. Spectrophotometric methods allowed to measure B-phycoerythrin content (UV-visible) and gave an indication on the protein structure (fluorescence). Micro-DSC analysis and electrophoresis complemented this structural investigation for all the protein fractions of P. cruentum extracts. Applying high hydrostatic pressure treatments up to 300 MPa during 5 min had no significant effect on B-phycoerythrin content and structure in P. cruentum extracts. Nevertheless, conformational changes of the protein are suggested by fluorescence yield decrease at 400 MPa, and protein aggregation of B-phycoerythrin, observed by Micro-DSC and electrophoresis, occurred at 500 MPa. Industrial relevance: The HHP process is an emerging technology for the microbiological stability of various food matrices, including the proteins of microalgae as natural colorant. The target pressure to stabilize is around 400 MPa. High hydrostatic pressure can be used on P. cruentum extracts up to 300 MPa without any change in protein structure, as the threshold of protein aggregation is observed at 400 MPa. The observed changes of the proteins structure after applying HHP above 400 MPa can have a strong impact at macroscopic scale on the food matrices: increase of turbidity, change of texture, stability of emulsion.