Chemical Composition and Bioactive Properties of Aqueous Extracts From Four Species of Marine Bivalves

This study evaluated the proximate composition, amino acid composition and bioactive properties of four marine bivalves namely Placuna placenta (Linnaeus, 1758), Placuna ephippium (Philipsson, 1788), Marcia hiantina (Lamarck, 1818), and Anadara inaequivalvis (Bruguière, 1789). Major proximate components of the bivalve tissues were moisture (74.27 ± 3.20– 80.18 ± 0.80 %), followed by protein (9.08 ± 0.50–13.54 ± 0.50 %), ash (1.87 ± 0.20–3.57 ± 1.00 %), and lipid (0.60 ± 0.06–1.27 ± 0.30 %). Lysine and threonine were the most abundant essential amino acids (EAAs) in the range of 4–10 % amino acid content, while arginine (7.1–9.8 %) and glutamic acid (4.4–9.1 %) were the most abundant of the non-essential amino acids (NEAAs). Marcia hiantina had the highest percentage of total EAAs and NEAAs at 17.3 % and 33.0 %, respectively. Samples were extracted using aqueous extraction, then subjected to biological assays to evaluate bioactivity and extraction in cold compared with hot water. Cold-water extract of M. hiantina demonstrated the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and ferric-ion reducing capacity (76.24 ± 7. 15 % and 1.58 ± 0.04 mM Trolox equiv.mL-1 sample, respectively) while the cold-water extract of P. ephippium exhibited the highest 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity at 93.67 ± 0.29 %. Moreover, hot-water extract of P. placenta demonstrated the highest angiotensin I-converting enzyme (ACE) inhibition at 76.01 ± 2.24 %. These results suggest that these four marine bivalve species might possess bioactive peptides eliciting antioxidant and anti-hypertensive activities which can be used as natural supplements and drug alternatives in lieu of synthetic medicines.