An optimised low-salinity seawater decolourising method produces decolourised seaweed (Kappaphycuz alvarezii) as semi-refined carrageenan raw material:

Semi-refined carrageenan (SRC) production from decolourised Kappaphycuz alvarezii treated by chemicals (CaCO₃) drives the search for ‘greener’ decolourisation methods to sustainably supply cheaper and energy efficient products. Therefore, a decolourisation method of low-salinity seawater (LSS) (3, 9 and 15 g/L) was investigated to replace CaCO₃. In addition, decolourised seaweed colour powder (DSP) and SRC colour, yield, viscosity and gel strength were used to screen the salinity treatments. SRC prepared from LSS (3 g/L) treatment demonstrated similar colour and physical properties to CaCO₃ treatments, which indicated low-salinity seawater (3 g/L) could replace CaCO₃ as a decolourising agent. Moreover, purity of SRC (3 g/L salinity) were confirmed by x-ray diffraction (XRD), scanning electron microscopy-energy-dispersive x-ray (SEM-EDX), and its functional group by fourier transform infrared (FTIR). In this study, waste seawater from LSS (3 g/L) exhibited radical scavenging properties. This decolourising method could be easily adopted by smallholder seaweed farmers in low- and middle-income countries.