Seaweeds are known to hold substances of high nutritional value; they are the richest resources of minerals impor-tant to the biochemical reactions in the human body. Seaweeds also hold non-nutrient compounds like dietary fiber andpolyphenols. However, there is not enough information on the mineral compounds of tropical seaweeds. Also we are inter-ested in the antioxidant activities of seaweeds, especially those in the tropical area. In this study, Indonesian green, brownand red algae were used as experimental materials with their mineral components analyzed by using an atomic absorptionspectrophotometer. The catechins and flavonoids of these seaweeds were extracted with methanol and analyzed by high per-formance liquid chromatography (HPLC); the anti-oxidant activities of these seaweeds were evaluated in a fish oil emulsionsystem. The mineral components of tropical seaweeds are dominated by calcium, potassium and sodium, as well as smallamounts of copper, iron and zinc. A green alga usually contains epigallocatechin, gallocatechin, epigallocatechin gallate andcatechin. However, catechin and its isomers are not found in some green and red algae. In the presence of a ferrous ion cata-lyst, all the methanol extracts from the seaweeds show significantly lower peroxide values of the emulsion than the control,and that of a green alga shows the strongest anti-oxidant activity. The highest chelation on ferrous ions is also found in theextract of this alga, which is significantly different from the other methanol extracts in both 3 and 24 h incubations.
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