Measurements of Protein Content in Aqueous and Alkaline Extracts from Brewer's Spent Grains (BSG): Insights into the Extraction Kinetics and Energy Consumption

The brewers’ spent grain (BSG) is a rich biomass matrix containing several compounds of interest that require urgent and suitable valorisation strategies, due to its high production volume in the brewing industry. Among the most widespread approaches is the preparation of extracts, targeting particular compounds or soluble and/or insoluble fractions, after operating pre-treatment processes. In the present study, extraction experiments are carried out with fresh untreated BSG, under very gentle extraction conditions (room temperature and moderate agitation, in the 0-5 h interval), and using different solvents: deionized water, 0.1 M NaOH and 0.5 M NaOH in a 1:5 m/v solid-to-solvent ratio. The extraction dynamics were followed by monitoring the dry matter (DM) content obtained in the extracts after a centrifugation step. The protein content is estimated in each case by means of two different methods: direct measurements of absorbance at 280 nm (using bovine serum albumin, BSA, and commercial whey protein isolate as standards) as well as using the Bradford colorimetric method and BSA standard; the consistency of these measurements is contrasted against the DM values. The apparent extraction kinetics were studied, using a saturation model; the coefficients and their range of uncertainty were obtained. Extraction efficiencies in the range 14.24%-53.60% g DM ext /g DM BSG are achieved, which correspond to extraction yields of 38.88-150.09 g DM ext /kg fresh BSG . In addition, the energy footprint of the process is estimated at laboratory scale.