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 °C except for that collected in September, which was observed to only be stable until 200 °C. Antioxidant activity of CSSA from different seasons was measured using DPPH• 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.

在不同季节（12月，4月，7月和9月）从突尼斯岛（Kerkennah，Sfax）收集的棕色海藻（Cystoseira schiffneri）中提取海藻酸钠。Schiffneri的结构特征和抗氧化性能海藻酸钠（CSSA）的特点。微量元素分析表明藻酸盐馏分中不存在氮和硫。所有藻酸盐分离株的糖醛酸和灰分含量较高，分别为47.4-66.4％和24.3-39.4％。ATR-FTIR，NMR和圆二色性数据表明，所有CSSA均为聚古龙酸酯型。使用高性能尺寸排阻色谱法测定的重均分子量显示出4.49至1230 kDa的变化。热重分析表明，除了9月份收集到的CSSA之外，CSSA一直稳定到400°C，直到9月份才稳定。使用DPPH•自由基清除，还原能力和Fe ²⁺来测量不同季节的CSSA的抗氧化活性。螯合能力测定。CSSA的抗氧化潜力随季节而变化，控制抗氧化性能的主要因素是分子量。