Influence of oven-drying pre-treatment on the metabolic profile of extracts from brewer’s spent grains

Extracts from untreated (fresh) and treated (oven-dried and ground) BSG, the most abundant residue from the brewing industry, were investigated through UHPLC–MS/MS metabolomic analysis to evaluate the effect of biomass pretreatment and extraction conditions on their chemical composition. Three extraction conditions were applied to each starting material, and the identified compounds were grouped into eight classes based on their chemical structure. The accumulated MS signal intensity of each class of compounds was then compared across the starting materials and the extraction conditions. The results showed that for some compound groups (e.g., sugars, amino acids, and phenolic compounds) drying was the main discriminating factor, while for others (lipids and hordatines) the determining factor was the extraction solvent. In addition, antioxidant capacity assays revealed that extracts obtained from untreated BSG with 40% hydroethanolic solvent displayed the highest activity. Overall, our data indicate that the energy- and time-consuming drying/stabilization pre-treatment step may be avoided. Given the predictable availability of BSG in both quantity and timing this is possible, although confirmation studies at pilot and industrial scale are needed.