## 3 Results and Discussion
### Purification of Crude Phycobiliprotein Extract
#### 3.3.2 Purification of Phycobiliprotein-Rich Extract Using Activated Carbon  
Using activated carbon to purify phycocyanin is an emerging approach with great potential, as it is inexpensive and straightforward [32]. This technique removes impurities while preserving the functionality of phycocyanin. The extract was purified with activated carbon by mixing it with different amounts of activated carbon (0.1, 0.25, 0.5, 2, and 4%, (\(w/v\))), with the effects of various concentrations on purity and recovery illustrated in Figure 6.  
Among the various tested concentrations, 0.5% activated carbon had the highest increase in extract purity, increasing from the initial purity of 1.12 \(\pm\) 0.06 to 2.55 \(\pm\) 0.06, and it was also significantly different from all the other samples (\(p\) < 0.05). PC recovery after purification with 0.5% of activated carbon was 90.88%. On the other hand, purification with 0.1% and 0.2% of activated carbon had a higher PC recovery \(-\)95.79% and 92.78%, respectively; however, the increase in purity was lower, with a final purity of 1.89 \(\pm\) 0.10  
Figure 6: Purity after using varied activated charcoal concentrations for purification (**A**). Phycocyanin and allophycocyanin recovery after purification with different activated charcoal concentrations (**B**). Image of obtained extract after addition of 0.5% activated charcoal (**C**). Values are expressed as mean \(\pm\) standard deviation, n = 3. Different lowercase letters indicate significant differences (\(p\) < 0.05). and 2.13 \(\pm\) 0.03 for concentrations of 0.1% and 0.2%, respectively. It should be noted that in the samples with the highest tested concentration (2 and 4%) of activated carbon, the colour of the extract was substantially reduced after centrifugation, indicating that these concentrations of activated carbon leads also to the absorption of PBP, as it is evident by the low recoveries (Figure 6B). The high surface area and porous structure of activated carbon enable the non-selective adsorption of impurities, such as pigments or other contaminants, resulting in the observed high purity. This known characteristic could explain the PBP losses observed in this study, especially at higher carbon contents. However, further studies and a deeper investigation of adsorption dynamics would give more information about the underlying purification mechanism. Nevertheless, despite the lack of molecular specificity, the attractiveness of activated carbon over other purification technologies, such as gel filtration or ion exchange chromatography, lies in its cost-effectiveness and scalability for industrial applications. In a previous study, [PERSON] et al. used a range of 1-10% of activated carbon for PC purification and reported the highest recovery (89%) using 1% [33]. However, the highest purity (1.2) was obtained with 7 and 8% concentrations of activated carbon and a 74% recovery, which is not in line with our observations. [PERSON] et al. used only a 0.5% concentration of activated carbon to purify PC extracts from a range of cyanobacterial strains [32]. They reported that purity after this method could vary from 1.76 to 3.1, depending on the type of cyanobacteria used and the growing conditions before the biomass is obtained. Applying these simple and cost-effective techniques improved the purity of the obtained PBP. Ammonium sulphate fractionation and activated carbon purification achieved a purity of 2.3 and 2.5, respectively, with high recovery rates. PBP extracts with PC purity above 1.5 are considered cosmetic-grade and have already found multiple applications in various cosmetic formulations, serving as colourants [64]. Considering the limited availability of natural blue pigments and the growing demand for natural and multifunctional ingredients in the cosmetic industry, simple and cost-effective approaches could further assist the development of new formulations and products.