Extracting proteins from Brewers’ spent grain using emerging technologies: Evaluating efficiency and use as emulsifier

Brewers' spent grain (BSG) is the main side-stream of the brewing industry with an annual production of 40 million tons of wet weight. BSG has a protein content of 15%–30% dry basis, which makes it an interesting material for protein extraction. Normally, extraction is performed under high temperatures or high alkaline conditions. In this study, microwave-assisted extraction, pulsed electric field, ultrasound, and ohmic heating were tested with the aim of improving protein content and protein recovery of BSG proteins without pH adjustment (pH 6) or at pH 9. Microwave-assisted extraction (33.7% protein recovery at pH 6 and 43.6% at pH 9) and ultrasound extraction (36.5% protein recovery at pH 6 and 58.6% at pH 9) led to higher protein recovery compared to the control extraction (29.5% at pH 6 and 37.5% at pH 9) at both pH levels. Furthermore, the results obtained showed that the use of ultrasound at pH 9 resulted in the highest protein content of 24.1%. The extracts were further tested for their emulsifying activity. Extracts produced from microwave-assisted extraction and ohmic heating could produce the smallest emulsion droplets (D[4,3] = 2.03 and 2.24 μm, respectively) and emulsions were visually stable for the first 2 days of analysis. Sample complexity, protein concentration, and sample absorption to oil/water interface could be responsible for lack of stability for longer times. The present study highlights the potential of emerging technologies as an alternative to harsh solvent usage in order to extract BSG proteins and their impact on protein functionality.