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 < 0.05) 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 < 0.05). 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.
Highlights
Lipid oxidation and microbial spoilage are the major deteriorative processes in foods, leading to unacceptability for the consumers and a loss in nutritional value
Total phenolic contents (TPC) of the same extract decreased, except for methanolic extract of S. polycystum, in which chlorophyll removal had no impact on TPC
The results indicated that methanolic extract of T. ornata could inhibit lipid oxidation, irrespective of chlorophyll removal
Summary
Lipid oxidation and microbial spoilage are the major deteriorative processes in foods, leading to unacceptability for the consumers and a loss in nutritional value. Oxidation leads to health disorders such as altherosclerosis and cancerogenesis (Kehrer 1993; Kranl et al 2005). The antioxidants and antimicrobial agents have been widely used to maintain the quality, acceptability, and safety of foods (Koleva et al 2003). Synthetic antioxidant and antimicrobial agents in food products are under strict regulation due to the potential health hazards (Kranl et al 2005). Seaweeds have been widely used for the production of hydrocolloids such as agar, carrageenan. Marine algae extracts were demonstrated to have strong antioxidant properties (Kuda et al 2005), protective effects against liver injury caused by carbon tetrachloride, antimicrobial activity and antiviral properties (Newman et al 2003). Small portion has been used as food, animal fodder, fertilizers, and for the production of hydrocolloids (Aungtonya and Liao 2002)
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