Recovery of sugars and amino acids from brewers' spent grains using subcritical water hydrolysis in a single and two sequential semi-continuous flow-through reactors.

This study evaluated the subcritical water hydrolysis (SWH) of brewer's spent grains (BSG) to obtain sugars and amino acids. The experimental conditions investigated the hydrolysis of BSG in a single flow-through reactor and in two sequential reactors operated in semi-continuous mode. The hydrolysis experiments were carried out for 120 min at 15 MPa, 5 mL water min, at different temperatures (80 - 180 °C) and using an S/F of 20 and 10 g solvent g BSG, for the single and two sequential reactors, respectively. The highest monosaccharide yields were obtained at 180 °C in a single reactor (47.76 mg g carbohydrates). With these operational conditions, the hydrolysate presented xylose (0.477 mg mL) and arabinose (1.039 mg mL) as main sugars, while low contents of furfural (310.7 µg mL), 5-hydroxymethylfurfural (<1 mg L), and organic acids (0.343 mg mL) were obtained. The yield of proteins at 180 °C in a process with a single reactor was 43.62 mg amino acids g proteins, where tryptophan (215.55 µg mL), aspartic acid (123.35 µg mL), valine (64.35 µg mL), lysine (16.55 µg mL), and glycine (16.1 µg mL) were the main amino acids recovered in the hydrolysate. In conclusion, SWH pretreatment is a promising technology to recover bio-based compounds from BSG; however, further studies are still needed to increase the yield of bioproducts from lignocellulosic biomass to explore two sequential reactors.