## 3 Results and Discussion
### Antioxidant Activity  
Oxidative bursts can be avoided by the action of antioxidants through different mechanisms, including the formation of chelate complexes with pro-oxidant metals, free radical scavenging, quenching of singlet oxygen and photosensizers, and the deactivation of peroxydinitrite and lipoxygenases [64]. Synthetic antioxidant drugs available on the market have certain side effects, which are not conducive to long-term use. Hence, interests are gradually focusing on natural antioxidants, which are safer than chemically synthesized antioxidants, and some of these antioxidants may be more efficient than synthetic drugs. Therefore, the present study aims to investigate the antioxidant potential of proteins and peptides derived from the cryptophyte microalga _Rlodomonas_ sp. through DPPH radical-scavenging and ferric reducing power assays. DPPH radical-scavenging activities were found to increase proportionately to the concentration in all tested samples (Figure 4a). The crude protein used at 1 mg/mL showed an interesting antioxidant activity against DPPH, reaching 74%. This antioxidant activity was much higher than that previously reported for proteins extracted from _Schizochytrium limacinum_ and _Porphyra columbina_[65; 66]. In concordance, the crude protein showed dose-dependent reducing capacities, with a maximum reached at 1 mg/mL concentration (Figure 4b). The important antioxidant activity obtained for crude protein may be due to the presence of amino acids involved in free radical deactivation. Antioxidant peptide molecules can achieve quenching of reactive oxygen/nitrogen species through two pathways, namely, hydrogen atom transfer (HAT) and single electron transfer (SET) reactions [67]. Particularly, Met has been considered an important free radical scavenger in biological systems [68]. This is due to the Met radical, which is very labile to oxidation and may potentially scavenge free radicals before they attack other amino acid residues critical to protein structure or function. To obtain additional structural information on the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Alcalase Hydrolysate**} & \multicolumn{2}{c}{**Pepsin Hydrolysate**} & \multicolumn{2}{c}{**Proteins**} & \multicolumn{1}{c}{**Wave Number**} & \multicolumn{1}{c}{**Functional Groups**} \\ \hline
**Wave Number (cm-1)** & **Area** & **Wave Number (cm-1)** & **Area** & **Wave Number (cm-1)** & **Area** & **Range (cm-1)** & **[57; 60; 61]** \\ \hline
1628 & \(-\)1118.183 & & & 1636 & 188.203 & 1700–1600 & C=O related to Amide I \\ \hline
1549 & \(-\)767.192 & 1571 & \(-\)1069.794 & & 1527 & \(-\)26.986 & 1590–1520 & N–H deformation and C–N stretch at Amide II \\ \hline
1460 & \(-\)98.967 & 1491 & \(-\)611.148 & & & & \\  & 1436 & \(-\)71.050 & & & & & COO- \\
1395 & \(-\)0.296 & & & & & & (C-terminal) \\  & & 1388 & \(-\)799.001 & & & & \\ \hline
1295 & \(-\)909.203 & & & & & & \\
1136 & \(-\)133.919 & & & 1235 & \(-\)272.163 & 1300–1100 & Amide III \\  & & 1125 & \(-\)308.975 & & & & \\ \hline  & & & 1042 & \(-\)308.375 & & \(-\)2188.419 & & \\
1035 & \(-\)175.511 & & & & & & \\ \hline
909 & \(-\)162.478 & 927 & \(-\)483.800 & & & & \\  & & 888 & \(-\)377.804 & & & & \\  & & 684 & \(-\)418.802 & & & & \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._antioxidant peptides derived from _Rhodomonas_ sp. protein hydrolysate, the active peptides need to be purified and their amino acid sequences should be investigated. The important antioxidant activity obtained for crude protein indicates that _Rhodomonas_ sp. could be a good candidate as a natural antioxidant source for use in the food and cosmetic fields. Moderate antioxidant activities were found for peptide hydrolyses obtained by enzymatic digestion using alcalase and pepsin, separately. This finding confirms the suggestion of [PERSON] et al. [69] that enzymatic hydrolysis could not increase antioxidant activity if the specific peptide having antioxidant activity was not liberated or the active peptide was inactivated by digestion.