Extraction, antioxidative, and antimicrobial activities of brown seaweed extracts, Turbinaria ornata and Sargassum polycystum, grown in Thailand

Abstract

Total phenolic content and antioxidative and antimicrobial activities of methanolic and ethanolic extracts from brown seaweeds, Turbinaria ornata and Sargassum polycystum, were determined. Among all extracts, methanolic extract of T. ornata contained the highest total phenolic content (2.07 mg catechin/g dry seaweed) (p .05) and exhibited the highest antioxidative activity as indicated by the greatest ABTS and DPPH radical scavenging activity as well as reducing activity power (RAP), compared with other extracts (p .05). When different concentrations of seaweed extracts (100–500 mg/L) were used, antioxidative activities were dose-dependent. Correlations between ABTS and DPPH radical scavenging activity; DPPH radical scavenging activity and RAP; ABTS radical scavenging activity and RAP were observed. Therefore, antioxidants in seaweed extracts possessed the capability of scavenging the radicals together with reducing power. The efficacy in prevention of lipid oxidation of methanolic extract of T. ornata in lecithin-liposome and linoleic oxidation systems was studied. The extract at levels of 100–500 mg/L could retard the oxidation, regardless of chlorophyll removal but its efficacy was lower than that of BHT at levels of 50 and 200 mg/L. For antimicrobial activity, all extracts could not inhibit the growth of Bacillus subtilis, Salmonella enteritidis, and Aspergillus niger, while Staphylococcus aureus was inhibited with the extracts at 500 mg/L.