Nutritional Properties, Antioxidant Activity, and Heavy Metal Accumulation in Selected Marine Macro-Algae Species of Sri Lanka

In recent years, the emergence of drug resistance and sensitivity in leading diseases has heightened global interest in natural nutraceuticals as primary health supplements. However, comprehensive scientific scrutiny is essential before marketing these as supplements. In this study, we assessed the nutritional composition, antioxidant activities, and trace metal accumulation in eleven selected Sri Lankan coastal seaweed species. Gracilaria corticata had the highest (p < 0.05) ash and crude fiber content among the species. Protein content ranged from 4.87% to 23.67% (DW), with Ulva rigida displaying the highest (p < 0.05). Crude fat content ranged from 0.09% to 4.13% (DW), with Cladophora herpestica having the highest (p < 0.05) crude fat content. Sargassam cinereum, Turbinaria ornata and Sargassum crassifolium had the highest (p < 0.05) TPC content (51.32 ± 0.61–28.90 ± 2.68 mg/GAE g) and the highest (p < 0.05) radical scavenging antioxidant activity compared to other seaweeds. The study findings indicate that most of the studied metals in seaweeds exceeded the WHO-recommended levels. Aluminum was the highest (p < 0.05) accumulated metal in seaweeds compared to other metals. Toxic heavy metals, such as arsenic, cadmium and chromium, levels in all of the studied seaweeds surpassed the WHO limits. While seaweeds displayed acceptable nutritional and antioxidant properties, heavy metal presence poses a potential health risk to consumers. Products using seaweeds with accumulated heavy metals may have lower nutritional quality. Thus, this study underscores the need for comprehensive scientific investigation before developing high-quality natural food products or supplements from seaweeds.