Antioxidant properties of by-products of polysaccharide extraction from brown seaweed Colpomenia peregrina

  Seaweed Colpomenia peregrine is a marine brown macro alga from Scytosiphonaceae family. Secondary metabolites are one of bioactive compounds which, along with polysaccharides, are located in the cell wall these algae. In the process of polysaccharide extraction, secondary metabolites are primarily removed and discarded in depigmentation step. While, this extract possesses precious bioactive compounds such as polyphenols, peptides, pigments, etc. Considering the side effects of utilizing synthetic antioxidants in food industries and the need to search for alternative compounds, executing new studies on antioxidant properties of these compounds is necessary. Therefore, the aim of current study is to evaluate the antioxidant properties of ethanol extract from seaweed C. peregrina. Seaweed C. peregrina was caught from Caspian Sea coastal area and washed with fresh water. Then, samples were dried at 60 °C and pulverized. The ethanol extract of dried seaweed powder was obtained using 80% ethanol at 60 °C for 2h. Then, solvent partitioning was respectively employed using hexane, chloroform, ethyl acetate and water as solvents. The antioxidant properties of crude and fractions were tested using DPPH radical scavenging activity, ABTS radical scavenging activity, reducing power, total antioxidant activity and total phenolic amount. The correlation between total phenolic content and antioxidant activity was also analyzed. The extraction yield of ethanol extract from C. peregrina was calculated as 5.4% of dried sample. Solvent partitioning of crude extract resulted in four fractions with the highest yield for water fraction (50%) and the lowest yield for ethyl acetate fraction (1%). The evaluation of antioxidant activity has revealed that the solvent partitioning is effectively capable of producing fractions with higher antioxidant properties. Among different fractions, ethyl acetate fraction exhibited the highest capability in DPPH radical scavenging (99.22%) at 1000 μg/ mL. The highest ABTS radical scavenging obtained for water (99.71%) and ethyl acetate (96.30%) fractions, respectively. Hexane, chloroform and water fractions exerted a similar ability with crude extract in reducing ferric ions. Conversely, ethyl acetate fraction showed the highest activity in reducing ferric ions (57.89%) and total antioxidant activity. The amount of total phenolic content of crude and fractions was measured between 125 to 278 mg TA/ g sample which indicated poor correlation with antioxidant activity. Results of current study revealed that secondary metabolites of ethanol extract from seaweed C. peregrina possess a notable antioxidant activity. Hence, after further studies, ethyl acetate fraction compounds could be introduced as a natural antioxidant in food systems