Protein extraction of brewers' spent grain using emerging technologies

In 2023, global beer production reached over 170 billion liters, including alcoholic-free beer. During beer production, fermentable sugars are released from the malt for later fermentation. The remaining insoluble pellet is called brewers’ spent grain (BSG). BSG is the main side-product of the beer industry and constitutes 85 % of the total waste. An estimated 20 kg of wet BSG is produced for each 100 L of beer. BSG contains between 15-30 % dw of protein, which makes it an interesting raw material in the food industry. Current research on protein extraction from BSG involves high pH or temperatures followed by acid precipitation.
In this study, we aimed to extract proteins under mild conditions using green technologies. Microwave-assisted extraction (MAE), pulsed electric field extraction (PEF), ohmic heating (OH), and ultrasound-assisted extraction (US) were tested either without pH adjustment and at pH 9. The temperature was kept below 50°C in all cases. Extracts were characterized by total protein content and yield, FTIR, surface hydrophobicity, SDS-page, and emulsifying properties.

US resulted in the highest protein yield of 58 % at pH 9 compared to 37 % for the control extraction, followed by MAE (44 % yield at pH 9). Significantly higher yield was observed in all cases at pH 9 compared to pH 6. The highest protein content was achieved with US at pH 9 with 24 wt%. The amide I and II bands were identified by FTIR, however, the spectra was dominated by carbohydrate peaks. Visible bands around 40 KDa were present on the SDS page. However, smaller size protein bands were also present.

The study showed that extracting proteins from BSG using new green technologies under mild conditions can be a promising and sustainable strategy.