Effects of extraction, purification, and drying on the antioxidant capacity of wheat bran extracts

Abstract

Background: Antioxidants (AO) present in wheat bran (WB) contribute to the prevention of chronic diseases such as cancer and type 2 diabetes. The choice of extraction technology is critical for obtaining biologically active compounds from plant material. Depending on the processing conditions, extracts obtained from the same raw material may vary in compositions, which directly affect their antioxidant potential (AOP).

Objective: This study aimed to evaluate the effect of different extraction, purification, and freeze-drying methods on the antioxidant potential (total antioxidant capacity – TAC, total phenolic compounds – TPC, total flavonoid compounds – TFC), as well as on protein and reducing sugar contents of wheat bran extracts, in order to identify the most effective approach for producing antioxidant-rich dry extracts.

Methods: Wheat bran extracts were prepared via maceration (MM, aqueous and ethanol), ultrasound-assisted extraction (UAE, aqueous and ethanol), and enzymatic aqueous extraction (EAE). TAC was evaluated using FRAP, ORAC and DPPH assays; , TPC by the Folin-Ciocalteu method, and TFC by the aluminum chloride method. Extracts were purified by either nylon-membrane filtration or ethanol (96%) precipitation and then freeze-dried with or without maltodextrin (MD).  Reducing sugars and proteins were quantified using the sulfuric acid method and Lowry/Bradford assays, respectively. Statistical analysis was conducted with STATISTICA 10.0.

Results: Enzymatic aqueous extraction (EAE) produced the highest TACFRAP (1,64 ± 0,03 μmol-eq. Q/ g of bran, p < 0.05) and the highest TPC (1.39 ± 0.12 μmol-eq. G/g of bran). The ethanolic UAE exhibited the highest  TACORAC and TACDPPH (8,12 ± 0,27 and 0,89 ± 0,001 μmol-eq. Q/g of bran, respectively, p < 0.05) but had lower TPC and TFC compared to other extracts.  Ethanol precipitation reduced protein content by 84-92% and sugars by 40% (p < 0.05), while increasing TACFRAP and TACORAC by over 60% (p < 0.05). Freeze-drying preserved high TAC values in both control and filtered extracts, regardless of maltodextrin (MD) addition

Conclusion: The choice of extraction method strongly affects the recovery of antioxidants from wheat bran. Enzymatic extraction combined with ethanol precipitation and freeze-drying produces extracts with enhanced antioxidant potential, reduced impurities, and preserved bioactivity, representing an effective strategy for obtaining antioxidant-rich wheat bran extracts for functional food and nutraceutical applications. This study provides the first comprehensive evaluation of this combined approach, offering a practical method for producing high-quality, antioxidant-rich wheat bran extracts.

Keywords: plant antioxidants, phenolic compounds, ultrasonic extraction, enzymatic extraction, freeze-drying, ethanol precipitation, optimization, functional food, nutraceutical applications