Ultrasound-assisted lipid extraction and antioxidant co-extraction from brewer's spent grain

Brewer's spent grain (BSG) is the primary solid side-stream of the beer production. Although it contains approximately 10 % lipids, research on BSG lipids remains limited. The cellular structure of BSG may hinder lipid extraction. Therefore, this study investigated the effects of ultrasound-assisted extraction (UAE) on lipid extraction kinetics, antioxidant co-extraction kinetics, and the quality of lipid extracts from BSG. To enable direct comparison, control extractions (CE) were conducted under identical conditions of solvent, treatment duration, and temperature but without ultrasound. UAE enhanced lipid extraction mainly through an ‘ultrasound-induced temperature increase’. Free fatty acids (FFA) were preferentially extracted, however, the extraction efficiency of FFA by UAE was not improved, likely due to the relatively low temperature increase in the initial stage of extraction and possible ultrasound-induced formation of FFA-protein complexes. Antioxidants such as phenolic compounds and carotenoids were co-extracted, with UAE effects being compound-specific. UAE significantly enhanced the co-extraction of phenolic compounds beyond the ‘ultrasound-induced temperature increase’, whereas carotenoid co-extraction appeared to be mainly attributed to the ‘ultrasound-induced temperature increase’. Lipid extracts obtained by UAE at high power density had the lowest FFA and the highest phenolic compound content. No evidence of lipolysis or lipid oxidation was observed during UAE. • UAE increases BSG lipid extraction kinetics mainly due to the temperature increase. • Free fatty acids are preferentially extracted. • UAE effect on antioxidant co-extraction kinetics is compound-dependent. • No pronounced lipolysis or oxidation is observed during lipid extraction.