Brewer’s spent grain lipids: characterization and the ultrasound effect on extraction, quality and oxidative stability

The valorization of waste streams from plant-based food processing is getting increasingly important. Brewer’s spent grain (BSG), the principal waste stream from beer production, contains valuable components such as protein, fibre, and lipids. Despite its potential, the current utilization of BSG is predominantly limited to low-value animal feed. Recent studies on the valorization of BSG particularly focused on proteins and fibres. However, there is a significant knowledge gap concerning lipids. Given the substantial quantities of BSG, we believe it is worthwhile to explore the potential of BSG lipids. As BSG structure may impede lipid extraction, this research examined the potential of ultrasound as a cell disruption technique to enhance extractability. Additionally, the quality and oxidative stability of the extracted lipids were assessed.
In this study, the BSG lipids were firstly characterised based on the fatty acid profile, lipid class composition, free fatty acid (FFA) and antioxidant (phenolic compound and carotenoid) content. Ultrasound-assisted lipid extraction (UAE) was performed with different power densities and the results were compared with those obtained through conventional extraction (CE) at different temperatures. Furthermore, the lipid extraction as the function of time was monitored by one kinetics model. Antioxidant co-extraction kinetics were also investigated. Quality characteristics including fatty acid profile, FFA and antioxidant content of extracted lipids were determined. Besides, the oxidative stability of extracted lipids during extraction and storage was also measured.
The results indicated that BSG lipids contain a high FFA content. The improvement of lipid extraction efficiency by ultrasound can be almost entirely attributed to the ultrasound-induced temperature increase. Lipids obtained by UAE at high power density contained the highest phenolic compounds and lowest FFA. No significant lipolysis or oxidation occurred during extraction.