Fractionation and structural characterization of antioxidant compounds from Sargassum horneri ethanol extract

Abstract

Sargassum horneri (S. horneri), a brown seaweed, contains health-beneficial phytochemicals. Air pollutants, the particulate matter cause harmful effects on human health via reactive oxygen species generated by oxidative stress. In this study, we extracted S. horneri with ethanol (SHE) and SHE was further fractionated with n-hexane (S-SHE), chloroform (T-SHE), ethyl acetate (P-SHE), and water (PS-SHE). Also, bioactive compounds (sterols, simple sugars, and phenolic acids) in SHE, SHE-R (residue of SHE extraction), and SHE fractions were analyzed using high-performance liquid chromatography (HPLC) with DAD and RID. Furthermore, in vitro antioxidant activities, and antioxidant activities against particulate matter induced oxidative stress were investigated. The highest total phenolic contents were found in P-SHE (31.91 mg GAE/g) and flavonoid contents were in T-SHE (320.60 mg QE/g). The SHE-R contained the highest sulfate (14.93%) and T-SHE had the highest reducing sugar (0.06%). The predominant sterol detected in SHE, SHE-R, and SHE fractions was fucosterol, which ranged from 2.13 to 6.23 mg/100 g and other sterols were not found. Fucose, fructose, glucose, sucrose, maltose, and lactose were found in SHE and two to four kinds of sugars were detected in SHE-R and SHE fractions. Gallic acid was the major phenolic acid compound in SHE and SHE fractions; however, no phenolic compound was detected in S-SHE. Either catechin or vanillic acid was found in T-SHE and P-SHE. The major phenolic compound in P-SHE was identified as gallic acid esterified glucose when analyzed using UPLC-Q-TOF-MS. SHE fractions showed higher antioxidant activities. Especially, P-SHE exhibited high activities in hydrogen peroxide scavenging (74.88%) and DPPH (70.63%), ABTS+ (43.62%) and hydroxyl radical scavenging (27.65%). When the oxidative damage induced by particulate matter at 0.125 mg/mL, the antioxidant activities of SHE, SHE-R, and SHE fractions were mostly decreased. These results suggest that bioactive compounds in S. horneri can be isolated to be used as a natural source of antioxidants for functional food ingredients, and effectively suppress the oxidative stress induced by particulate matter.