# Microalgae as Potential Sources of Bioactive Compounds for Functional Foods and Pharmaceuticals
## 3 Results and Discussion  
### Evaluation of Bioactivities of Microalgal Extracts  
#### 3.1.1 Antioxidant Activity  
Antioxidant activity was evaluated using the DPPH assay, which measures the ability of microalgal extracts to scavenge free radicals. From the twenty-two extracts tested, only the ethanol extracts from all species, as well as the water extract from _Porphyridium_ sp. (POC) and the ethyl acetate extracts from _Nannochloropsis_ sp. (NANNO), _Phaodactylum tricornutum_ (PHA) and _Skeletonema_ sp. (SKE) had scavenging activity over 50% at 0.1 mg/mL (Table 1). The IC\({}_{50}\) of these extracts varied between 0.408 and 1.66 mg/mL (Table 1), and the most antioxidant extracts were _Phaodactylum tricornutum_ ethyl acetate extract (PHA EA), _Skeletonema_ sp. ethanol extract (SKE ET), _Skeletonema_ sp. ethyl acetate extract (SKE EA) and _Haematococcus pluvialis_ ethanol extract (HPL ET). As ethyl acetate is more effective in extracting non-polar compounds (such as carotenoid, pigments, polyphenols, and fatty acids) this may indicate that these compounds contribute significantly to the antioxidant activity of the studied microalgae [35]. Ethanol is very efficient in the extraction of polyphenols, although it is also able to extract some non-polar compounds as fatty acids, which are present in microalgae species and are believed to be responsible for at least some of the antioxidant activity [36; 37]. Water is particularly effective in extracting polar compounds such as phenolic compounds and polysaccharides. Nonpolar molecules (such as PUFAs, which have known antioxidant properties) are not extracted, which can decrease the antioxidant activity of these extracts in comparison to other more nonpolar solvents [38]. It is reported that _Porphyridium curetum_ is rich in a variety of compounds, which have known antioxidant activity such as exopolysaccharide (which are thought to make up about 50% of the total biomass of this microalgae), pigments (especially phycoerythrin), lipids and polyunsaturated fatty acids, which may explain why _Porphyridium_ sp. presented high antioxidant activity in both water and ethanol extracts in this study [25]. Results for _Haematococcus pluvialis_, P. tricornutum_ and _Skeletonema_ sp. are similar to those from [PERSON] et al. [28] and [PERSON] et al. [39], where astaxanthin and fucoxanthin, are believed to be mainly responsible for the antioxidant activity. Similarly, _Nannochloropsis_ sp. was reported as being a promising source of antioxidant compounds due to its high content of polyunsaturated fatty acids and pigments [26]. Our results suggest that some of the studied extracts could be a dietary source of antioxidants, representing a promising path for prevention or treatment of oxidative stress-related diseases. The redox-metal chelation activity of the crude ethanol, ethyl acetate and water extracts from the nine microalgal species was firstly assessed at a concentration of 0.1 mg/mL, and the IC\({}_{50}\) was only determined for those extracts able to chelate at least 60% of the existing copper and iron in solution (Table 2). The extracts with the lowest IC\({}_{50}\) values for copper chelating activity were POC ET (0.144 mg/mL), TIL W (0.184 mg/mL) and SKE ET (0.195 mg/mL). The extracts where iron chelating activity was highest (>50% chelation) and whose IC\({}_{50}\) was determined were: TCTP4 W (0.385 mg/mL), TIL W (0.403 mg/mL), NANNO W (0.279 mg/mL), POC W (0.508 mg/mL), TIL ET (0.207 mg/mL) and POC ET (0.0854 mg/mL). Fractionation was performed on the extracts with the lowest IC\({}_{50}\) values for copper and iron chelation assays. The ethanol extracts of _Porphyridium_ sp. and _Skeletonema_ sp. yielded three fractions (hexane, dichloromethane, and ethyl acetate). As a new extract had to be prepared for the fractionation, this was also analyzed (Table 3).