Benefits and challenges of fortified beverage systems with brewer's spent grain-derived protein isolates

Plant protein soft drinks align with current consumer demand for hydration, nutrition and sustainability yet faces challenges due to protein aggregation and precipitation in an acidic environment. This study evaluated the effects of two different barley and rice protein isolates, EverPro® Dark Fraction (EDF) and a decolourised version, EverPro® Light Fraction (ELF), at ingredient inclusion levels of 0%, 2.5%, 5% and 10% in diverse beverage systems including water as a control, apple juice, a full sugar and sugar free carbonated drink, a sweetened ice tea, an unsweetened black tea and a non-alcoholic beer. Physicochemical properties were comprehensively assessed. Protein inclusion, particularly at 10%, elevated pH to a more neutral range (from 3.1 and 4.88 to 5.0 and 7.8). Increasing the addition of both ingredients also elevated viscosity (from 1.04 and 1.46 to 2.54 and 5.43 mPa s), density (0.999 and 1.045 to 1.030 and 1.074 g cm⁻³) as well as lubrication properties of all beverages with ELF exhibiting higher values compared to EDF. Dispersion stability improved dramatically including turbidity and particle size at higher inclusion levels (10%), influenced by changes in pH further from the proteins isoelectric point. Low inclusion levels (2.5%) caused maximum turbidity and separation rate. Principal component analysis revealed distinct clustering by beverage matrix and protein type, with apple juice most affected. These findings demonstrate a step towards soft drinks fortified with upcycled protein from brewers spent grain with added nutritional benefits for future commercially potential.