Solid-State Fermentation of Brewery Spent Grains to Enhance Biomolecule Extraction

In the present work, brewer’s spent grain, BSG, the main by-product of beer production, was applied for the recovery of total polyphenols (TPs). Whole and ground BSG (wBSG and gBSG), derived from a Pilsen beer, was subjected to a solvent extraction using ethanol/water (50:50 v/v), and then, to improve TP recovery, microwave, ultrasound bath or probe pre-treatments were applied. The highest total phenolic content (TPC) (5.8 mg GAE/gDW) was obtained with gBSG pre-treated with the ultrasound (US) probe for 15 min at 250 W. Solid-state fermentation (SSF) with Phanerochaete chrysosporium, in microcosms was investigated to improve the release of TPs. Microcosms were monitored by means of CO2 production, the total proteins, and laccase activity. Fungal growth on gBSG, after only 10 days of fermentation, resulted in a 30% increase in the TPC compared to the unfermented substrate. Applying US probe-assisted extraction to fermented, ground BSG resulted in a 51% improvement compared to the untreated sample.