Extracting Organic Compounds from Brewer's Spent Grain by Various Methods

Brewer's spent grain is a brewing industry waste product that contains various valuable biologically active substances. However, polymers can complicate their extraction. This article focuses on innovative extraction methods, including sustainable deep processing that destroys the internal structures of plant matrix. The research objective was to review publications on the sustainable brewer's spent grain processing as a source of secondary raw materials and plant matrix organic compounds. The study featured the last 5–10 years of foreign and domestic analytical and technical publications on grain structure and extraction methods. Unlike the traditional acidic, alkaline, and enzymatic methods of grain processing, physical and mechanical methods aim at extracting biogenic peptides, phenolic compounds, and fatty acids. The nature of the processing depends on the type of the extracted compound. Thus, for the extraction of reducing compounds intended for sorption, exposure to high temperatures (≥ 150°C) is the most effective method. A combined treatment with acids or alkalis of the cellulose-lignin complex makes it possible to achieve a 76.2% yield of hemicelluloses. Acid hydrolysis of arabinoxylans is effective at 120–160°C. Alkaline hydrolysis combined with physical treatment makes it possible to reach 60% of arabinoxylans in a mix with phenolic compounds. When extracting nitrogen-containing, phenolic, and lipid compounds, the degree of grinding of the biomaterial and the organic solvent is of great importance. The optimal degree makes it possible to preserve the spatial structure while maintaining a high yield (86%) of organic compounds. Ultrafiltration concentrates the isolated biogenic compound and preserves its activity with a high yield of up to 95%. The analysis proved that the brewer's spent grain processing can be both feasible and environmentally friendly. It produces a high yield of pure organic compounds, e.g., peptides, phenolic compounds, fatty acids, etc.