The pre-extracted fraction was freeze-dried and the chemical composition was determined.
The components were moisture 1.8%, carbohydrate 19.15%, protein 2.51%, phenolic 8.4%, ash 42.07%, trace sulfate, and other 26.07%, respectively.
High ash content was observed (42.07%), which means part of salts can be removed from seaweed sample during the ethanol pretreatment step.
Previous work indicates that the main carbohydrate content in this fraction was mannitol (Foley et al., 2012).
The 1H NMR analysis of pre-extraction fraction suggested that in addition to mannitol as major carbohydrate content, there are some possible lipids in the pre-extraction fraction (Fig. A).
The phenolic content was determined to be 8.4% by the Folin–Ciocalteau (FCR) method, as it is well known that phenols can be used as antioxidant reagent (Zhang et al., 2014), the antioxidant activity of pre-extracted fraction was also investigated, and this will be discussed later together with fucoidan, which was demonstrated to exhibit antioxidant activity in our previous work