Abstract:

The Soxhlet extraction product from Porphyra haitanensis was fractionized according to solubility difference in different solvents into petroleum ether (PE)-soluble fraction, ethyl acetate (EA)-soluble fraction, n-butanol-soluble fraction and water-soluble, and the extraction product and its fractions were tested and compared for their DPPH radical scavenging capacity and reducing power and their contents of total polyphenols and total flavonoids were also determined. All these fractions had an antioxidant effect in a significant dosage-dependent manner in the range of 0.2 to 1.5 g/L and the EV-soluble fraction exhibited the highest ranking for both DPPH radical scavenging capacity and reducing power and followed by the n-butanol-soluble fraction, the PE-soluble fraction and the water-soluble fraction. The EA-soluble fraction at a concentration of 1.5 g/L exhibited a reducing power absorbance of 1.97, which was higher than that (1.90) of 80% tea polyphenols, a commercial product and close to that (2.00) of BHT. Likewise, the EV-soluble fraction ranked first for both the contents of total polyphenols (69.84 mg GAE/g dry weight) and total flavonoids (299.49 mg RE/g dry weight), and the water-soluble fraction last, with a total polyphenol content of 11.1 mg GAE/g dry weight and a total flavonoid content of 32.36 mg RE/g dry weight. Therefore, phenolics are mainly distributed in mid-polarity solvents rather than high-polarity ones. Moreover, the contents of total polyphenols and total flavonoids of the Soxhlet extraction product and its four fractions were linearly plotted against their DPPH radical scavenging capacities or reducing power at 1 g/L, respectively, and the results showed that correlation coefficients were 0.9311 and 0.7530 for the relationship between total polyphenol content and DPPH scavenging capacity or reducing power and 0.8899 and 0.7211 for the relationships between total flavonoid content and DPPH scavenging capacity or reducing power, respectively. Based on these investigations, it can be concluded that polyphenlics mainly contribute to the antioxidant effect of Porphyra haitanensis.

Key words: Porphyra haitanensis, anti-oxidation, DPPH, reducing power, total polyphenol content, total flavonoid content, correlation