Influence of the extraction solvent on phenolic content, antioxidant, antimicrobial and antimutagenic activities of brewers' spent grain

Recent advances in biotechnology ensure that brewer's spent grain, the major by-product of the brewing industry, is no longer regarded as a waste but rather a rich source of bioactive compounds. With a hypothesis that the antioxidant constituents of this vegetable waste could be efficiently extracted and valorized, this comparative study assessed the capability of different solvents to extract bioactive compounds and evaluate their antioxidant, antimicrobial and antimutagenic activities. From the twelve tested, the highest concentrations in phenolics (97.83-114.23 mg GAE/100 g DW) were obtained for the methanolic extracts and the aqueous mixtures of ethanol and acetone (60/40 and 40/60, v/v). These data were strengthened by the HPLC-ESI-MS phenolic profile and also by the radical scavenging activities determined by DPPH and ABTS assays. All investigated extracts exert antimicrobial activity against different strains, but the extracts with low phenolic content and low antioxidant activity manifested similar or higher antimicrobial activity (especially towards Candida albicans) and significantly enhanced antimutagenic activity. The results emphasize the importance of selecting the proper extraction solvent in order to obtain extracts rich in biomolecules with specific bioactivities (antioxidant, antimicrobial and/or antimutagenic).