Sustainable Production of Phenolic Compounds From Brewers' Spent Grain: Optimization of Operational Extraction Conditions.

Abstract

This study aimed to evaluate the effect of different extraction conditions on the recovery of phenolic compounds from brewers' spent grain (BSG) and their antioxidant capacity. A Plackett-Burman design (PBD) was first applied to identify the key variables influencing the extraction process, followed by response surface methodology (RSM) to optimize the conditions for maximizing phenolic compound yield and antioxidant activity. The optimized extraction parameters included a drying temperature of 50°C, a liquid/solid ratio of 56.5 mL/g, and an extraction temperature of 69.7°C. Experimental validation confirmed that the predicted values for total phenolic content (2.68 mg AGE/g dm) and antioxidant capacities (1.20 mg TE/g dm for DPPH and 5.81 mg TE/g dm for ABTS) were in agreement with experimental data within a 95% confidence level, demonstrating the reliability of the models used. Despite the high phenolic content and antioxidant activity, the extracts showed no antimicrobial effect against Escherichia coli O157:H7 or Listeria innocua. These findings highlight the potential of BSG as a source of antioxidants, reinforcing its possible applications in the food, packaging, pharmaceutical, and cosmetic industries as a natural additive. Additionally, optimizing the extraction process contributes to the valorization of this agro-industrial by-product, promoting sustainability and circular economy practices.