Evaluation of different pretreatment strategies for protein extraction from brewer’s spent grains

Brewer´s spent grain (BSG) is an agro-industrial residue rich in proteins, which correspond to approximately 18–30% (w/w) of its composition in a dry weight basis. In the present study, different pretreatment strategies including alkaline, acid, enzymatic and hydrothermal, and their combinations, were evaluated and compared with the aim of extracting protein from BSG. From the different evaluated options, one-step dilute acid pretreatment (11,400 mg H₂SO₄/g BSG, 121 °C for 1 h) was able to extract 90% of total protein present in BSG. Sequential alkaline and dilute acid pretreatment increased the protein extraction to 95%. Hydrothermal pretreatment at 60 °C resulted in a protein extraction of approx. 64–66%, which was lower than those achieved by the chemical methods but still relevant as it was obtained under non-optimized process conditions. In addition, the selectivity of the process for protein recovery was higher for hydrothermal pretreatment than for the chemical processes. Hydrothermal pretreatment was then found as an interesting option for protein extraction from BSG, being also advantageous in terms of costs (requires low temperature and no addition of chemicals), and more environmentally friendly.