Comparative assessment of extraction, composition, and in vitro antioxidative properties of wheat bran polyphenols

Bran is the major byproduct in wheat processing with low development and utilization rates. Polyphenols are a major bioactive component in bran and are beneficial to human health. In this study, wheat bran polyphenols were extracted by four methods and analyzed by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC‒MS). Among the methods, the alkaline hydrolysis method had the highest polyphenol yield (4.38 ± 0.18 mg GAE/g DW). The antioxidant activity results revealed that polyphenols obtained by alkaline hydrolysis extraction showed the lowest 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diamine salt (ABTS) IC50 value (31.94 ± 0.79 μg/mL) and 2-diphenyl-1-picrylhydrazyl (DPPH) IC50 value (30.64 ± 0.81 μg/mL). The surface microstructure analysis showed that alkaline hydrolysis can effectively destroy the cellulose structure and facilitate bounded polyphenol release. The qualitative and quantitative results indicated that the crude extracts mainly contained nine polyphenols with the highest content of trans-ferulic acid. For purification, preparative high-performance liquid chromatography (Prep-HPLC) was utilized to isolate two high-purity polyphenols (component 1 and component 2, 43.43 ± 2.34% and 60.82 ± 1.49% purity, respectively), and their trans-ferulic acid content and antioxidant properties were also assessed. Eventually, in vitro evaluations indicated that wheat bran polyphenols effectively reduced oxidative stress damage (p < 0.05) by synergistic effects.