Oxidative stability of brewer's spent grain lipid extracts during storage

Brewer's spent grain (BSG), the largest side-stream of the brewing industry, remains understudied in terms of its lipids. This study investigated the oxidative stability of BSG lipid extracts during storage. First, BSG lipid extracts were obtained under various extraction conditions: (i) ultrasound-assisted extraction (UAE) at high and low power densities, and (ii) control extraction at three different temperatures. For comparison in determining the oxidative stability, commercial soybean oil with a similar fatty acid composition was included. Second, the initial composition of all lipid samples was determined. Then, the oxidative stability was assessed through an accelerated storage experiment at 37 °C for 8 weeks. Results showed that BSG lipid extracts exhibited a markedly lower oxidative stability compared to commercial soybean oil, regardless of the extraction condition. In addition, BSG lipid extracts obtained by UAE at high power density exhibited slightly slower oxidation. The high free fatty acid (FFA) content of BSG lipid extracts was hypothesized to be a key factor explaining the poorer oxidative stability compared to soybean oil, despite the higher degree of unsaturation and lower amount of antioxidants in the latter. Moreover, the results indicated that the effect of UAE on lipid oxidative stability during storage was limited.