Extraction and assessment of the colouring capacity of Arthrospira platensis-derived pigments

This study presents a zero-waste biorefinery approach for the sequential extraction of phycocyanin and chlorophyll from Arthrospira platensis, followed by the valorisation of the remaining biomass as a plant biostimulant. Natural deep eutectic solvents were screened for phycocyanin recovery, with the mixture proline:glycerol:sorbitol:water (1:1:1:13 molar ratio) showing the highest potential (1.15 g⋅100 g^-1; p < 0.05). An initial ultrasound-assisted cell wall disruption step significantly enhanced phycocyanin yield by 400–450 % relative to the untreated control (p < 0.05). A response surface methodology optimised extraction achieved a recovery yield of 8.26 g⋅100 g^-1 at 39.7 °C and 127.9 min. The phycocyanin-rich extract was used to mimic the blue colour of commercial blue gin, with a minimal colour difference (ΔE) of 4.53. Subsequent chlorophyll extraction from the phycocyanin leftovers yielded an extract that successfully coloured a commercial green alcohol-free apple liquor (ΔE = 3.93) and green gin (ΔE = 1.65). Finally, the residual biomass demonstrated a significant biostimulant capacity, increasing the germination index of various seeds by 80–150 % compared to water (p < 0.05). This work highlights the potential of A. platensis as a sustainable source for natural colourants and agricultural inputs.