Alginic acids and alginates have important applications in food, medicine, pharmaceutical industry, dentistry and textile. The sodium alginate from Nizimuddinia zanardini (an Iranian brown seaweed) was extracted with high voltage electrical discharge to investigate the influence of this extraction method on its structural and physico-chemical characteristics. The extracted alginate had a M/G ratio of 1.22, a molecular weight of 119 kDa, a polydispersity index of 2.7 and an intrinsic viscosity of 170.8 mL/g. The rheological properties of an alginate solution (2% w/v) indicated a Newtonian fluid type of behavior. The influence of pH on the flow behavior of this solution was investigated. The solution had a Newtonian behavior at pH 7.0, an intermediary behavior between Newtonian and non-Newtonian shear thinning at pH 6.0 and 5.0 and a clearly shear thinning behavior at lower pH values (4.5 and 3.0). Its antioxidant activity was tested by diphenyl picrylhydrazyl radical scavenging and hydroxyl radical-scavenging activity showing its potential for food preservation. High voltage electrical discharge improved the antioxidant properties explained by the co-extraction of phenolic compounds. The stability of emulsion increased with concentration of alginate and was reported at 94.7% ± 0.1 at 2% (w/v) concentration. The stability of emulsions was not affected by temperatures up to 55 °C and was resistant to pH changes.