Recovering Phytochemicals from a Brewery By-product: A Sustainable Reuse Proposal Using a Lactic Acid-Based Deep Eutectic Solvent

Abstract

Hot trub (HT), a nutrient-rich by-product of beer production, remains underutilized despite its potential for resource recovery. This study explores the valorization of HT, producing two phytochemical-rich extracts with potential functional applications and a protein-rich solid residue that can be repurposed as a food ingredient. The extraction of phytochemicals from HT, particularly xanthohumol (XN), was evaluated through a sequential extraction process employing a deep eutectic solvent (DES) composed of choline chloride (ChCl) and lactic acid (Lac) in a 1:2 molar ratio, followed by ethanol-based solvent extraction. The influence of temperature and DES-to-HT ratios was evaluated, as defined by the experimental design. DES selectively extracted XN, reaching a maximum yield of 36 µg/g at 50 °C with 8 g of DES and 4g of HT. However, sequential extraction with ethanol on DES-treated solid residues at 50 °C and equal DES-to-HT mass ratios yielded a higher XN extraction (~114 µg/g), underscoring DES effectiveness as a pretreatment. The temperature influenced the extraction of other phytochemicals, including desmethylxanthohumol and phenolic acids, contributing to enriched antioxidant activity. Structural analysis of HT after extraction revealed modifications, such as shifts and loss of functional chemical groups induced by DES, improving phytochemical accessibility for the ethanol extraction step. The analysis of the proposed process using the Path2Green metric demonstrated a strong alignment with the principles of green chemistry and the circular bioeconomy.