Investigation of physicochemical, nutritional, and sensory qualities of muffins incorporated with dried brewer's spent grain flours as a source of dietary fiber and protein

Brewers' spent grain (BSG) is the major byproduct of brewing beer, rich in protein and dietary fiber. This study investigated the effect of two drying methods (impingement and hot-air drying) on chemical composition, physicochemical properties, and bioactive compounds of BSGs from three different brewers (BSG1, BSG2, and BSG3), and then evaluated the quality and consumer acceptance of BSG flour fortified muffins. Results showed that impingement drying led to significantly lower moisture content (MC, 1.33-1.87 g/100g) and water activity (a(w), 0.04-0.07) of BSGs than hot-air drying (5.44 to 5.57 g/100 g and 0.19 to 0.20, respectively). Among different dried BSGs, impingement dried BSG3 achieved the highest protein (18.03 g/100 g dry matter [DM]), total phenolic content (TPC, 2.21 mg GAE/g DM), radical scavenging activity (RSA, 1.58 mg AAE/g DM), and total flavonoid content (TFC, 0.68 mg QE/g DM), and retained lighter color (L*, 54.68) and higher total dietary fiber (TDF, 42.40 g/100 g DM), which was selected for making BSG-fortified muffins. BSG3 was substituted 1:1 as white: whole wheat flour at three concentrations (10, 15, and 20 g/100 g flour mix) for muffins (BSG10, BSG15, and BSG20, respectively). BSG15 provided higher protein (13.11 g/100 g DM), TDF (16.88 g/100 g DM), and higher bioactive compounds compared to control and retained brighter color of muffin compared to BSG20, showing no difference in firmness and overall liking compared to the control muffin. This study demonstrated that impingement dried BSG could be utilized as a functional ingredient in muffins to add value to the food chain providing nutritional and environmental benefits. Practical Application This study reported the benefit of impingement drying method for the retention of physicochemical quality and bioactive compounds of brewer's spent grains (BSG) produced from three different brewers in comparison with hot-air drying. The study also reported that muffins fortified with BSG flours (15% replacement of wheat flour) yielded a 23% increase in total dietary fiber and 13% increase in protein without affecting consumer acceptance of the products. This information is essential for developing value-added applications of BSG, a byproduct from brewing industry, as a functional ingredient to make nutritive baking goods, such as muffins, for promoting human health.