## 3 Results and Discussion
### Bioactivity of the Microalgae Extracts  
#### 3.4.1 Total Phenolic Content (TPC) and Antioxidant Activity (AA) of the Microalgae Extracts  
In the present study, the TPC varied significantly among the microalgae species (Table 5). _Odontella_ sp. exhibited the highest total phenolic content (TPC) among the microalgae species investigated. _Limnospira_ sp. presented the highest antioxidant activity (AA) in the ABTS, DPPH, and ORAC assays. Conversely, _Porphyridium_ sp., _Nannochloropsis_ sp., and _Tetraselmis_ sp. showed the lowest TPC, with _Tetraselmis_ sp. and _Nannochloropsis_ sp. generally demonstrating the weakest antioxidant activities (Table 5). Recent studies consistently demonstrate that TPC varies significantly among microalgae species. This variation is primarily due to species-specific metabolic pathways, genetic differences, and environmental responses [48]. Such inter-species differences have important implications for selecting microalgae strains for specific bioactive applications (e.g., nutraceuticals, antioxidants). [PERSON] et al. [49] determined the TPC of an ethanolic extract from _Limnospira_ sp., reporting a value of 9.919 \(\pm\) 0.446 mg GAE/g of extract dry weight (DW), which is similar to the value observed in the present study (9.7 \(\pm\) 0.6 mg GAE/g DW). [PERSON] et al. [50] assessed the antioxidant activity of an aqueous extract from _Limnospira platensis_, reporting DPPH and ABTS scavenging activities of 40.65 \(\pm\) 0.21% and 81.93 \(\pm\) 0.61%, respectively. [PERSON] et al. [39] noted that the TPC in spirulina (51.20 mg/mL) was higher than that in its ethanolic extract (49.48 mg/mL), while the aqueous extract had the lowest value (15.26 mg/mL). \begin{table}
\begin{tabular}{c c c c c} \hline
**Microalgae** & **TPC** & **ABTS** & **DPPH** & **ORAC** \\
**Species** & **(mg GAE/100 mg DW)** & & **(\(\upmu\)mol TE/100 mg DW)** & \\ \hline _Limnospira_ sp. & 0.97 \(\pm\) 0.06 \({}^{\text{bc}}\) & 2.85 \(\pm\) 0.45 \({}^{\text{a}}\) & 2.28 \(\pm\) 0.06 \({}^{\text{a}}\) & 18.38 \(\pm\) 1.00 \({}^{\text{a}}\) \\ _Dunaliella_ sp. & 1.52 \(\pm\) 0.09 \({}^{\text{b}}\) & 2.75 \(\pm\) 0.36 \({}^{\text{ab}}\) & 1.14 \(\pm\) 0.06 \({}^{\text{c}}\) & 13.77 \(\pm\) 1.38 \({}^{\text{b}}\) \\ _Lobosphaera_ sp & 1.07 \(\pm\) 0. [PERSON] et al. [51] obtained an ethanolic extract from _Dunaliella tertioleta_ using ultrasound-assisted extraction, with a TPC of 515.72 \(\pm\) 4.67 \(\upmu\)g GAE/g and a DPPH radical scavenging activity of 40 \(\pm\) 1.41%. [PERSON] et al. [52] investigated the TPC and AA of ethanolic extracts of _Lobosphaera_ sp., evaluating the effects of high-pressure processing (HPP) on frozen versus freeze-dried biomass. The highest TPC (11.50 \(\pm\) 0.21 mg GAE/g DW) was achieved when HPP was applied to frozen biomass, which is comparable to the value found in the present study (10.7 mg GAE/g DW). The lowest TPC (4.61 \(\pm\) 0.06 mg GAE/g DW) was observed following HPP on freeze-dried biomass. Additionally, freeze-drying was found to significantly reduce DPPH radical scavenging activity (by approximately 3%) compared to freezing (around 2%). [PERSON] et al. [53] evaluated the ABTS and DPPH assays of a methanolic extract of _Nantochloropsis__oculata_ obtained via ultrasound-assisted extraction. IC50 values were 96.95 \(\pm\) 1.68 \(\upmu\)g/mL for ABTS and 52.10 \(\pm\) 0.85 \(\upmu\)g/mL for DPPH. [PERSON] et al. [43] reported a TPC of 26.42 \(\pm\) 1.5 mg GAE/g for an ethanolic extract, while an ethyl acetate extract followed by hexane separation (EAH) yielded a higher TPC of 40.61 \(\pm\) 1.8 mg GAE/g. In the DPPH assay, IC50 values were 13.9 \(\upmu\)g/mL (EAH), 31.84 \(\upmu\)g/mL (ethanol), and 48.01 \(\upmu\)g/mL (acetone). [PERSON] et al. [54] reported a TPC of 43.6 \(\pm\) 1.2 \(\upmu\)mol GAE/g DW and an ORAC of 6948 \(\pm\) 1532 \(\upmu\)mol TE/100 g DW for a methanolic extract of _Nantochloropsis__granulate_. [PERSON] et al.