Chemical characterization and biochemical activity of polysaccharides isolated from Egyptian Ulva fasciata Delile

•Ulvan from Ulva fasciata Delile was studied using distilled water, HCl and EDTA forming F-I extractions.•F-II was obtained by sequential extraction from the previous extractions using NaOH.•Evaluation of these different extraction media effect in testing their biological activities (antioxidant, anti-inflammatory, antimicrobial, and antifouling) was investigated.•The antimicrobial activity showed that the microbial species Vibrio damsela was the most susceptible to DW (F-II) with an inhibition zone (30 mm) at the concentration of 112 and 150 mg/ml.•F-I extract using HCl showed the best antioxidant capacity (63.3 µmole AAE/g).•The F-II EDTA extract demonstrated the highest anti-inflammatory activity at both concentrations 25 and 50 mg/l being 94.0 and 91.40%, respectively.•F-II DW in descending concentration order (150, 100, 50 mg/l) followed by HCl at 100 mg/l were the most effective extracts for the antifouling property. This study gives updated information on the isolation of ulvan from green alga Ulva fasciata Delile in Egypt through isolation and chemical characterization of sulfate polysaccharides by two sequential extraction steps using different solvents; distilled water, HCl and Na2EDTA forming fraction I (F-I). Fraction II (F-II) was obtained from remaining seaweeds using NaOH to give FDWNaOH, FHClNaOH, and FEDTANaOH. All products obtained were tested for their biological activities. The highest polysaccharides total extraction yield was 11.8% for water extract (F-I and F-II). The highest protein content was found in FEDTANaOH (2.44%). The highest sulfate content was recorded for F-I (HCl) (21.38%). Total carbohydrates range was 11.99–63.90% for F-I and 15.06–76.65% for F-II. Monosaccharides; galactose, rhamnose, and uronic acid were detected at all fractions, with concentrations varying from 0.11 to 1.34%, from 0.61 to 1.81% and from 11.06 to 19.30%, respectively. 1H NMR of F-II demonstrated the signals of ring and methyl protons of polysaccharide. The appearance of the stretching bands of the sulfate ester (C-O-S) and sulfate groups (S=O) in the FT-IR spectrum of FHClNaOH confirmed the presence of sulfated polysaccharides, typical of ulvan. The microbial species Vibrio damsela was the most susceptible to FDWNaOH, followed by Aeromonas hydrophila and Vibrio fluvialis with inhibition zones of 30, 22, 22 mm at 150 mg/ml, respectively. FDWNaOH was the most effective fraction having antifouling property. The highest antioxidant activity was observed