Polyphenols separated from Enteromorpha clathrata by one-dimensional coupled with inner-recycling high-speed counter-current chromatography and their antioxidant activities

Algae polyphenols, derived from marine algae, have gained much attention in recent years for their diverse biological activities, such as antibacterial, antioxidant, anti-inflammatory, and cholesterol-lowering effects. Extraction, purification, and identification of individual compounds are difficult due to the broad range of molecular sizes and complex structures. In this paper, an efficient separation of polyphenols from Enteromorpha clathrata (E. clathrata), commonly found in the southeast coast of China, was achieved using ultrasonic-assisted extraction and multistage extraction followed by one-dimensional coupled with inner-recycling high-speed counter-current chromatography. The structure was identified by mass spectrometry and nuclear magnetic resonance spectra. Seven compounds with a purity of greater than 90% were separated from the ethyl acetate extract of E. clathrata, and identified as hydroquinone, gallic acid, (−)-epigallocatechin, caffeine, (−)-epicatechin, (−)-epigallocatechin-3-O-gallate, and epicatechin-3-O-gallate. These compounds were first separated and identified from E. clathrata. All of the six polyphenols exhibited potent antioxidant activity measured as 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity, while (−)-epicatechin and epicatechin-3-O-gallate showed poor hydroxyl radical scavenging capacity, in comparison with Vitamin C (VC). The antioxidant activity of polyphenols with the same number of benzene rings was positively proportional to the number of phenolic hydroxyl groups. Esterification appeared to enhance the antioxidant activity of catechin and reduce the hydroxyl radical scavenging capacity of gallic acid. Our results about the separation, identification, and antioxidant activity of polyphenols from E. clathrata provide a basis for further elucidating the relationship between structure and antioxidant activity, which will promote the development and utilization of E. clathrata antioxidants.