The antioxidant activities of the aqueous and ethanolic extracts of three New Zealand surf clam species (Tua Tua (Paphies donacina), Diamond Shell (Spisula aequilatera) and Storm shell (Mactra murchisoni)) were evaluated and presented as relative activities by comparing with a standard synthetic antioxidant (ascorbic acid). The ethanolic extracts were further fractioned into four parts (petroleum ether (pe), ethyl acetate (ea), n-butanol (nb) and the final aqueous residue (w)). Two types of antioxidant assays were employed to test for antioxidant activity. The DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, to test the scavenging ability of the clam fractions, and the Cupric Ion Reducing Antioxidant Capacity (CUPRAC) assay to evaluate their copper ion reducing ability. Results showed that the in vitro antioxidant activities of all fractions of the three NZ surf clams tested exhibited dose dependency, and increased with increasing concentration of the extract. The pe and ea fractions of all clam species showed higher cupric ion reducing capacity than ascorbic acid and the other fractions tested. All fractions had very strong radical scavenging ability, with the aqueous fraction of the Diamond shell having the least DPPH radical scavenging ability of 57.08% at 50µg/mL.

This study forms the first comprehensive report on the nutraceutical properties of the New Zealand surf clams as natural sources of antioxidants.