The antioxidant potential of the New Zealand surf clams
Introduction
The wide diversity of marine organisms contained in the world’s oceans offers a rich source of natural products (Wijesekara, Pangestuti, & Kim, 2011) and, as such, is regarded as the largest remaining reservoir of natural molecules to be evaluated for drug activity. Marine-derived bioactive peptides have been shown to possess many physiological functions including antihypertensive action or angiotensin-I-converting enzyme (ACE) inhibition (Je, Park, Byun, Jung, & Kim, 2005). Extensive research has shown the usefulness of the surf clams, both nutritionally and medically. Clams are important recreational and commercial resource in many countries (McLachlan et al., 1996).
Individuals are exposed to oxidants, both endogenous and exogenous, since the moment of conception. Reactive oxygen and nitrogen species are generated in vivo and cause damage to DNA, lipids, proteins and other bio-molecules (Halliwell, 1996). DNA damage can occur, for example, when hydroxyl radical, a highly reactive oxygen species (ROS), reacts with DNA bases by adding to double bonds of DNA bases and by abstracting an H atom from the methyl group of thymine and each of the C–H bonds of 2́-deoxyribose (Cooke, Evans, Dizdaroglu, & Lunec, 2003). Antioxidants are, therefore, needed to prevent the formation and to oppose the actions of oxidants. Antioxidants can be consumed in the diet and are synthesised in vivo in humans. Synthetic antioxidants have been invented, tested for acute toxicity and proposed as an addition to naturally occurring antioxidants. Unfortunately, recent reports have revealed that these synthetic antioxidants may be associated with toxic and carcinogenic effects (Zhang et al., 2010). As a part of society’s demand for a better lifestyle and increased longevity, consumers have developed an increasing interest towards consuming ‘nutraceuticals’ and functional foods rich in natural bioactive compounds (Fung, Hamid, & Lu, 2013). In an attempt to address this interest, there has been a dramatic increase in the number of investigations aimed at identifying dietary compounds from natural sources which may be effective in preventing diseases caused by oxidative damage (Tierney, Croft, & Hayes, 2010).
Research on surf clams have been carried out in different parts of the world, as it is known to exhibit a variety of biological activities. It has been reported that the extracts of certain molluscs like abalone, oyster and clams have shown both antibacterial and antiviral activities (Lin-rui, 2012). An extract from the edible clam Mercenaria mercenaria prevented the development of transplanted sarcoma 180 and Krebs-2-ascites tumors in Swiss mice (Schmeer & Huala, 1965). Chang, Li, Sun, Yang, and Sun (2012) reported that polysaccharides from the Chinese surf clam (Mactra chinensis) have scavenging activity against superoxide anion and hydroxyl free radicals in a concentration-dependent way. Furthermore, the aqueous and alcoholic extracts from Mactra veneriformis showed antioxidant potentials using various in vitro assays (Luan, Wang, Wu, Jin, & Ji, 2011). It has also been reported to show detoxification, cyst elimination, protecting the body cells from mutation and decrepitude (Leng, Liu, & Chen, 2005), as well as decreasing blood sugar and lipid levels. Surf clam extracts have also shown to have hepatoprotective, antihypertensive, antineoplastic, antimicrobial, hypocholesterolemic, and antiulcer effects (Lin et al., 2010, Ramasamy and Balasubramanian, 2012).
Surf clams, like most seafood, contain hydrophilic or lipophilic antioxidant compounds, such as carotenoids, free amino acids and polyunsaturated fatty acids. These antioxidant compounds are most likely responsible for the therapeutic activities of surf clams (Luan et al., 2011).
There are seven main species of surf clams in New Zealand: Tua tua – Paphies donacina (PDO), Diamond shell – C. aequilatera (SAE), Trough shell – Mactra discors (MDI), Storm shell – Mactra murchisoni (MMI), Moon shell – Dosinia anus (DAN), Fine dosinia – Dosinia subrosea (DSU) and Frilled venus – Bassina yatei (BYA). Four out of those seven are given more attention: PDO, SAE, MMI and DAN (Ministry for Primary Industries., 2012). None of the New Zealand surf clams has been studied for their antioxidant potential despite being a popular export to Asian seafood market. The present study was undertaken to evaluate, for the first time, the antioxidant potentials of three most harvested and exported New Zealand surf clam species, Diamond shell (C. aequilatera), Storm shell (M. murchisoni) and Tua tua (P. donacina).
Section snippets
Clam collection and maintenance
Clams were obtained from Cloudy Bay Clams Ltd (Fig. 1). All water used in this process is USFDA approved and regularly monitored to maintain the highest possible quality. Prior to export, the water is cooled to below 10 °C as required by New Zealand Food Safety Authority. The clams are packed into Polystyrene boxes (to regulate temperature) and freighted dry to the end user – Auckland University of Technology (AUT).
Chemicals and reagents
Methanol, n-Butanol, Petroleum spirit and Ethyl acetate were purchased from
Major content of extracts
The carbohydrate, protein and lipid content of each fraction of each species were measured and presented in Table 1. Carbohydrate and protein are the major components of the crude water extraction for all species. Lipid is the major component of ethanolic extract of all species, and most of it was extracted into the pe fraction. More protein/peptide component can be found in ea and nb fractions. Protein/peptide component is present at noticeable level in all fractions (Table 1).
DPPH scavenging activities of New Zealand surf clams
The radical
Conclusion
Our results showed that the New Zealand surf clams are rich in phenolic constituents and demonstrated good antioxidant activity measured by two in vitro assays. The results revealed that all fractions tested with the CUPRAC assay were statistically significant higher than ascorbic acid. With the DPPH assay, results showed that surf clam species also had high radical scavenging ability. These seafood, rich in flavonoids and phenolic acids could be a very good source of natural antioxidants.
Acknowledgements
This research was partially supported by the Cloudy Bay Clams Ltd., the Faculty of Health and Environmental Sciences, Auckland University of Technology (AUT), and the AUT Strategic Research Investment Fund.
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