The brown seaweed Cystoseira schiffneri as a source of sodium alginate: Chemical and structural characterization, and antioxidant activities

Sodium alginates were extracted from brown seaweeds (Cystoseira schiffneri) collected from a Tunisian island (Kerkennah, Sfax) in different seasons (December, April, July and September). The structural features and antioxidant properties of C. schiffneri sodium alginates (CSSA) were characterized. Micro-elementary analysis showed the absence of nitrogen and sulfur in alginate fractions. All alginate isolates were high in uronic acids (47.4-66.4%) and ash (24.3-39.4%). ATR-FTIR, NMR and circular dichroism data showed that all CSSA were of the polyguluronate-type. Weight-average molecular weight determined using high performance size exclusion chromatography showed variations ranging from 4.49 to 1230 kDa. Thermogravimetric analysis suggested that CSSA were stable until 400 degrees C except for that collected in September, which was observed to only be stable until 200 degrees C. Antioxidant activity of CSSA from different seasons was measured using DPPH center dot radical-scavenging, reducing power and Fe2+ chelating ability assays. Antioxidant potential of CSSA varied significantly with respect to the season and the main factor controlling antioxidant properties was the molecular mass.