Exploring and strengthening the potential of R-phycocyanin from Nori flakes as a food colourant

[Display omitted] •R-phycocyanin (R-PC) is purified and characterized from dried Nori flakes.•SAXS data revealed a trimeric structure of R-PC resembling a hollow cylinder model.•R-PC has moderate pH stability, being more stable at acidic than alkaline pH.•Treatment of R-PC at 60 °C has detrimental effects on R-PC colour and activity.•Immobilization of R-PC into alginate beads strongly improves its thermal stability. This study aimed to purify, characterise and stabilise the natural food colourant, R-phycocyanin (R-PC), from the red algae Porphyra spp. (Nori). We purified R-PC from dried Nori flakes with a high purity ratio (A618/A280 ≥ 3.4) in native form (α-helix content 53%). SAXS measurements revealed that R-PC is trimeric ((αβ)3) in solution. The thermal denaturation of α-helix revealed one transition (Tm at 52 °C), while the pH stability study showed R-PC is stable in the pH range 4–8. The thermal treatment of R-PC at 60 °C has detrimental and irreversible effects on R-PC colour and antioxidant capacity (22 % of residual capacity). However, immobilisation of R-PC within calcium alginate beads completely preserves R-PC colour and mainly retains its antioxidant ability (78 % of residual capacity). Results give new insights into the stability of R-PC and preservation of its purple colour and bioactivity by encapsulation in calcium alginate beads.