*2.1. Sequence Analysis of the Main Peptides of OPs*

As shown in Figure 1, the peaks of OPs were mostly in the range of 300 to 900 *m*/*z*. Overall, 177 peptides, with molecular weights ranging from 550.250 to 1387.697 Da, and an intensity ranging from 3,857,400 to 171,200,000, were identified from the OPs. The peptide fingerprinting of 40 characteristic peptides in OPs was analyzed using liquid chromatography–tandem mass spectrometry (LC-MS/MS). The scores for evaluating the matches between the theoretical and experimental mass spectrums were obtained by comparing the UniProt database; 20 peptide sequences with higher scores are listed in Table 1. Of interest, they contain a higher percentage of hydrophobic amino acids, such as proline (P, 37/180 residues in 20 peptides), valine (V, 14/180), and alanine (A, 8/180). Specific amino acid motifs, such as PVX, was repeated six times, and PxxP was repeated eight times, X being either a glycine, serine, or a proline residue, x being either an alanine, glycine, valine, threonine, asparagine, leucine, glutamic acid, aspartic acid, or an arginine, can be recognized. Hydrophobic amino acids proline or proline-rich peptides were reported to possess good anti-Cd, anti-oxidation, and anti-inflammatory properties [17–22].

**Figure 1.** Total ion chromatogram of peptides from oyster enzymatic hydrolysates (OPs).


**Table 1.** Main peptide sequences of OPs.
