Improved antioxidant activities of brown seaweed Ecklonia radiata extracts prepared by microwave-assisted enzymatic extraction

Seaweeds are important sources of bioactive compounds with potential use in functional foods and nutraceutical products. This study aims to investigate the extraction efficiency of phlorotannins and antioxidant compounds of a South Australian brown seaweed Ecklonia radiata by enzymatic and microwave-assisted enzymatic extraction in order to evaluate their uses as potential functional food ingredients. A selected group of carbohydrases (Viscozyme, Celluclast, and Ultraflo) and proteases (Alcalase, Neutrase, and Flavourzyme) has been applied to improve the extraction efficiency, alone and intensified with microwave heating, using conventional acid-base and water extractions as controls. The antioxidant activities of the extracts were evaluated using both ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) assays. Significantly higher yields in total phlorotannin content (TPC) and antioxidant activities of the extracts were achieved by enzymatic and microwave-assisted enzymatic extraction. Microwave-assisted Viscozyme extraction for 5 to 30 min was the most effective process with an extraction yield achieved of 52 %. The extract had a TPC of 4.4 g phloroglucinol equivalents (PGE).100 g⁻¹ dry weight (DW) and antioxidant activities of 29.7 mmol FeSO₄ equivalents.100 g⁻¹ DW and 740.1 μmol Trolox equivalents (TE).g⁻¹ DW. In contrast, the conventional acidic extraction for 24 hours resulted in a TPC of 3.4 g PGE.100 g⁻¹ DW and antioxidant activities of 21.1 mmol FeSO₄ equivalents.100 g⁻¹ DW and 512.4 μmol TE.g⁻¹ DW. Extracts of brown seaweed E. radiata have potential for use in value-added products for nutritional purposes, using the microwave-assisted enzymatic extraction techniques.