## 2 Results and Discussion
### In Silico Predictions of Potential Antioxidant Peptides  
BIOPEP-UWM(tm) data base tool was used to identify the antioxidant potential of highest-ranking peptides. Peptide sequences were analyzed based on the profiles of potential bioactive peptides reported in the literature and databases as well as the frequency of occurrence of fragments with a given activity [19]. Identified peptide sequences were submitted to the BIOPEP as query sequences and selected the \"antioxidant activity\" as bioactivity of interest. Tables 2 and 3 represent the in silico predictions of antioxidant potential of amino acid sequences found in flower and internal organs, respectively. According to the BIOPEP-UWM(tm) data base, 5 out of 8 peptides from flower and 2 out of 6 peptides from internal organs were identified as potential antioxidative peptides. Interestingly, all the three body parts of the sea cucumber shared similar bioactive sequences, namely GPP, WPL and MM. In general, amino acid residues including G (glycine), P (proline), W (tryptophan), L (leucine) and M (methionine) are recognized as some of the most established hydrophobic amino acids associated with antioxidant activity [5; 7; 20]. For example, tryptophan is an electron-dense aromatic residue that can contribute to the chelation of prooxidant metal ions. Moreover, the indole side chain of tryptophan can scavenge free radicals by electron donation [21]. Similar findings were reported by [PERSON] et al. [15] in Alcalase-produced peptide fractions from Atlantic Sea cucumber samples. Furthermore, the authors indicated that antioxidant potential of peptides produced using Alcalase was higher than that of trypsin-produced peptides due to the presence of the above-mentioned amino acid residues in their sequences [15]. In addition, the common amino acid sequence found in the sea cucumber body parts, GPPGPQWPLDF, contained phenylalanine (F). Phenylalanine can also act as a hydrogen donor to scavenge free radicals [22]. Presence of hydrophobic and aromatic amino acids is considered as key attributes to the antioxidative property of bioactive peptides [23]. Several antioxidant peptides identified from marine invertebrates including shrimp, jelly fish confer that peptides having most hydrophobic amino acids in their sequences possess strong antioxidant activities, including radical scavenging, reducing power, and inhibition of lipid peroxidation [24] GP (glycine-proline) sequence and particularly the occurrence of proline (P) in high proportion in the entire peptide enhanced its radical scavenging ability, in addition to the direct contribution of tryptophan [25]. When considering lipid peroxidation, it is presumed that increased lipid solubility of peptides due to the presence of hydrophobic amino acids can facilitate the interaction with radical species [22; 24]. Therefore, the current findings support the fact that sea cucumber-derived peptides may have the potential to inhibit the lipid peroxidation process. In addition, the synergism of amino acid residues present in the sequence may \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Total Identified Peptides** & \multirow{2}{*}{**PepRank**} & \multirow{2}{*}{**Peptide Sequence**} \\  & **over 0.9 Threshold** & & \\ \hline Flower & 8 & 0.96 & GPPGPQWPLDF \\  & & 0.94 & GPPGRGPTGRMG \\  & & 0.94 & GPGGGPGPGM \\  & & 0.93 & APDMAFPR \\  & & 0.92 & GGFPGGPG \\  & & 0.92 & GPGMMGP \\  & & 0.90 & GPPGASGLGLAGSM \\  & & 0.90 & GPSGPGPGP \\ \hline Internal organs & 6 & 0.96 & GPPGPQWPLDF \\  & & 0.94 & GEPFKF \\  & & 0.93 & APDMAFPR \\  & & 0.92 & PGGPGPGM \\  & & 0.92 & GPGMMGP \\  & & 0.90 & DPIFFPS \\ \hline \hline \end{tabular} G—Glycine, P—Proline, Q—Glutamine, W—Tryptophan, L—Leucine, D—Aspartic acid, F—Phenylalanine, T—Threonine, M—Methionine, A—Alanini, R—Arginine, S—Serine, I—Isoleucine, K—Lysine.  
\end{table} 
Table 1: Bioactive potential of identified peptides according to PEPRANK. also contribute to antioxidant properties [24; 25; 26].