Study on ultrasound-assisted extraction of bound polyphenols from wheat bran and analysis of antioxidant activity

Wheat bran, a major by-product of wheat processing, is rich in polyphenolic compounds and exhibits significant antioxidant activity. However, its utilization in food applications remains relatively low, leading to resource wastage. In order to enhance the effective utilization of wheat bran in the development of whole-grain functional food, the Box-Behnken method was used to optimize the extraction process of bound polyphenols from wheat bran by single-factor experiments. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to analyse the components of polyphenols in wheat bran. Moreover, the study also examined the antioxidant capacities of bound polyphenols and free polyphenols from wheat bran, with V_C as a control. The results indicated that the optimal extraction conditions for bound polyphenols were a liquid-to-solid ratio of 31 mL/g, an alkali concentration of 9 mol/L, ultrasonic time of 60 min, and an ultrasonic power of 260 W. Under these conditions, the extraction yield of bound polyphenols reached 13.01 mg/g, which was close to the predicted value of 13.12 mg/g by the regression model, demonstrating excellent model fitting. Preliminary identification by UPLC-MS/MS revealed that both the bound and free polyphenols were composed of nine phenolic compounds, including quercetin, rutin, and p-coumaric acid, but their compositional profiles exhibited differences. Antioxidant experiments revealed that the IC₅₀ values of bound polyphenols for DPPH· and ABTS·⁺ were 0.053 1 mg/mL and 0.033 7 mg/mL, respectively. These values were significantly(P<0.05)lower than those of the free polyphenols (0.117 6 mg/mL and 0.082 7 mg/mL). In the concentration range of 0.01~0.10 mg/mL, the scavenging ability of bound polyphenol ·OH was strong. Correlation analysis showed that the contents of polyphenols were negatively correlated with the IC₅₀ values of DPPH·, ABTS·⁺ and ·OH. Scanning electron microscopy (SEM) further confirmed that ultrasonic cavitation enhanced polyphenol release by disrupting the wheat bran’s fibrous microstructure. This study optimized the extraction process of bound polyphenols from wheat bran, providing a theoretical basis for the high-value utilization of wheat bran. It holds significant importance for promoting the efficient development of food resources and the advancement of functional food research.