Antimicrobial, antioxidant and free radical-scavenging capacity of brown seaweed himanthalia elongata from western coast of Ireland

Water, methanol and mixtures (20-80%) thereof have been used for the extraction of phenolic compounds from Irish brown seaweed Himanthalia elongata for studying its antimicrobial and antioxidant properties. The 60% methanolic extract exhibited significantly (P<0.05) the highest value of yield (6.8±0.24%), total phenol (286.0±4.61mg gallic acid equivalents/g), flavonoid (109.8±2.68mg quercetin equivalents/g) and condensed tannin content (35.6±1.03mg catechin equivalents/g). Antimicrobial activity of 60% methanolic extract tested from disc diffusion and broth dilution methods was effective against various food spoilage and pathogenic bacteria studied. The same extract exhibited statistically highest reducing power and antioxidant capacity against DPPH radical, metal ions, lipid peroxides and hydrogen peroxide radicals. The UV-visible spectroscopy showed absorption maxima at 205 and 260nm and the presence of hydroxyl group (3,431cm^-1) and an aromatic ring (around 1,465, 1,505 and 1,624cm^-1) in Fourier Transform Infrared spectroscopy, suggested the presence of phenolic compounds in the extract. PRACTICAL APPLICATIONS: In recent years, much attention has been focused on the use of natural preservatives to enhance the quality, safety and stability of ready-to-eat food products. These products also undergo gradual changes during storage, due to autoxidation, which releases reactive oxygen species including free radicals into the food. The consumption of seaweed as food and nutraceutical has been well known in the East. Nowadays, increasingly seaweeds are being investigated for the biological activity of their extracts which are finding hundreds of applications in pharmaceuticals, biotechnology and food preservatives. The present study demonstrates that H. elongata contains excellent antimicrobial and antioxidant properties which can provide opportunities for the application of seaweed extract as natural food preservative or nutraceutical for possible application in food and dietary supplemental products for health promotion.