THE EFFECT OF SOLID-STATE FERMENTATION ON THE PHENOLIC ACID CONTENT OF DIETS CONTAINING BREWER SPENT GRAIN

Introduction: The generation of by-products in the brewing industry, especially brewer spent grain (BSG), has aroused interest in its valorization due to its nutritional value and phenolic composition. Solid-state fermentation (SSF) emerges as a sustainable alternative for the valorization of BSG, allowing the release of bioactive compounds through the enzymatic action of microorganisms. goal: To evaluate the effect of SSF with Aspergillus oryzae on the content of phenolic acids in diets containing BSG. methodology: Pilsen BSG was obtained from a craft brewery in Rio de Janeiro and submitted to fermentation with Aspergillus oryzae (10.7 spores/g) at 30 °C for 72 hours. Diets without BSG, with unfermented BSG (RNF) and with fermented BSG (RF) were prepared manually in the laboratory. For the analysis of phenolics, two extractions were performed: free phenolics, obtained with 80% ethanol in a shaker (10 min, 25 °C, 200 rpm) and centrifugation (5000×g, 10 min, 25 °C); and bound phenolics, extracted from the pellet treated with NaOH (40 °C, 90 min), acidified to pH 2 and centrifuged (5000×g, 5 min, 25 °C). The supernatant was mixed with ethyl acetate, centrifuged (10000×g, 5 min, 10 °C) and evaporated in rotavapor. Both extracts were resuspended in a solution of 2% methanol, 5% acetonitrile, and 93% water and analyzed by HPLC-DAD. findings: RF showed a higher concentration of free phenolics (2.28 ± 0.04 mg/100g), especially ferulic acid (1.34 ± 0.03 mg/100g), significantly higher than the other formulations (p < 0.05). For bound phenolics, RF also stood out, reaching 31.54 ± 0.27 mg/100g, a value 13 times higher than free phenolics, with a predominance of ferulic acid (9.22 ± 0.02 mg/100g) and p-coumaric acid (13.48 ± 0.64 mg/100g). In contrast, RNF showed much lower levels (2.3 ± 0.10 mg/100g) of bound phenolics. In addition, compounds such as 4-hydroxyphenylacetic acid and 4-vinylphenol were detected exclusively in RF, suggesting metabolic formation during fermentation. Discussion: The increase in free phenolics in RF may be attributed to the action of hydrolytic enzymes produced by the fungus, such as cellulases and xylanases, which degrade the plant cell wall and favor the release of compounds. Conclusion: Fermentation of BSG with Aspergillus oryzae significantly increases the content of phenolic compounds, both free and bound, and also promotes the formation of exclusive metabolites. Thus, fermented BSG is configured as a promising functional ingredient, reinforcing its applicability in food formulations aimed at nutritional and antioxidant enhancement.