Chemical characterization and cellular responses to brewer’s spent grain extract: insights into antioxidant properties and redox homeostasis

Brewer’s spent grain (BSG), the main solid by-product of the brewing industry, represents about 85% of the waste generated throughout the production process and has attracted interest due to its nutritional value and phenolic composition. Its bioactive compounds, including phenolic acids and flavonoids, support investigations into its antioxidant capacity and potential biological effects. This study aimed to characterize the phenolic profile and antioxidant capacity of BSG and investigate its cellular effects in a prostate cancer cell line. The BSG sample originated from a Pilsen-type brewing process using a malt bill composed of 96% Pilsen malt and 4% Cara Light malt. The aqueous extract containing free phenolic compounds was obtained through sequential solid–liquid extraction assisted by ultrasound for a total of 30 min. Total phenolic content was determined using the Folin–Ciocalteu method, antioxidant capacity was assessed by DPPH and ABTS assays, and phenolic compounds were characterized by high-performance liquid chromatography with diode-array detection (HPLC-DAD). Apoptosis was evaluated by flow cytometry in PC-3 cells treated with 3.5 mg/mL of extract for 24 h. Catalase activity was determined in cell lysates obtained from PC-3 cells treated with 3.5 and 5.0 mg/mL of extract for the same period. The results showed that the extract exhibited a total phenolic content of 4.74 ± 0.20 mg gallic acid equivalents (GAE)/g, with DPPH and ABTS values of 0.080 ± 0.01 and 0.038 ± 0.00 µmol Trolox equivalents (TE)/g, respectively. HPLC-DAD identified (+)-catechin (1.19 ± 0.01 µg/mL) as the only compound detected among the analytes evaluated. This finding is consistent with previous reports of catechin in BSG, although its recovery may depend on extraction conditions and matrix characteristics. At 3.5 mg/mL, early and late apoptosis accounted for 0.06 ± 0.02% and 1.31 ± 0.17% of cells, respectively, with no significant increase compared with the control. In contrast, catalase activity decreased from 16.29 ± 1.52 U/L in the control group to 11.25 ± 0.33 U/L and 5.43 ± 0.44 U/L at 3.5 and 5.0 mg/mL, respectively, corresponding to reductions of approximately 31% and 67% (p < 0.05). This concentration-dependent decrease suggests a possible modulation of cellular antioxidant defenses, although its implications for redox homeostasis remain to be investigated. Further studies should investigate the cellular mechanisms underlying this response and assess whether processing strategies can enhance the recovery of phenolic compounds bound to the lignocellulosic matrix, potentially improving the biological effects of BSG extracts. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.