Protein Composition and Postprandial Aminoacidemia of Biscuits Fortified with Brewer’s Spent Grain and Fermented Brewer’s Spent Grain in Individuals with Metabolic Syndrome

Brewer’s spent grain (BSG), the main side-stream of beer brewing, is an abundant and low-cost source of plant protein with limited digestibility. Fermentation pre-treatment may improve protein quality by altering amino acid composition and increasing protein accessibility. This study investigated whether the solid-state fermentation of BSG with Rhizopus oligosporus could improve amino acid composition and further elicit a greater postprandial amino acid response after the consumption of BSG-incorporated biscuits in adults with metabolic syndrome (MetS). Control biscuits (100% wheat flour) and biscuits with a 30% substitution of autoclaved BSG and fermented BSG were prepared. Compositional improvements were evaluated via an analysis of total and free amino acids and the amino acid score calculated against adult indispensable amino acid requirements. Fifteen adults with MetS then consumed 90 g of each biscuit in a randomised, double-blind, crossover trial, with postprandial plasma amino acids assessed over 120 min. Incorporating BSG increased the total amino acid content in biscuits, while fermentation further increased free amino acid content. The lysine amino acid score also increased from 0.57 (Control) to 0.81 (fermented BSG). Despite these compositional improvements, postprandial total and essential amino acid responses did not differ between biscuits, indicating a disconnect between improved protein composition and postprandial amino acid responses in individuals with MetS.