Compositional dynamics, volatome profiling, and hyperspectral-based predictive modeling for quality monitoring of brewer's spent grain during storage

Brewer’s spent grain (BSG) is a nutritionally rich by-product of brewing. However, its short shelf life, driven by environmental conditions, limits its applications beyond animal feed. This study investigates the effect of storage conditions (4, 20, and 35 °C) on BSG quality using non-invasive hyperspectral imaging (HSI) and invasive analytical techniques. Significant degradation of sugars (78.2–79.0%), fats (21.4–33.3%), starch (14–19%), protein (9–15%), and hemicellulose (20.3–34.4%) occurred during storage at 20 and 35 °C. In contrast, phenolic content increased by 30–130%, accompanied by a 1.7–7.8-fold increase in antioxidant activity and a pH shift from 6.4 to 8.8. A total of 65 volatile compounds exhibited temperature and time-dependent changes. Key off-flavor compounds such as 1-octen-3-ol, formic acid, octanic acid, butanoic acid, 2-butanone, and amide were associated with rancid, sour, cheesy, earthy, and bitter aromas in BSG stored at 20 °C and 35 °C. Significant changes in color, pH, stickiness, and odor were evident after 24 h at 20°C and 12 h at 35°C. KEGG pathway analysis revealed that pyruvate metabolism, cutin, suberine, and wax biosynthesis, alpha-linolenic acid metabolism, and tyrosine metabolism were the dominant metabolic pathways. HSI combined with machine learning accurately predicted key quality parameters, including total phenols (R 2 p = 0.9908, RMSEp = 0.1492), total color change (R 2 p = 0.9680, RMSEp = 0.8285), sugar (R 2 p = 0.9917, RMSEp = 0.6038), protein (R 2 p = 0.9756, RMSEp = 1.9467), pH (R 2 p = 0.9037, RMSEp = 0.2605), and fat (R 2 p = 0.9866, RMSEp = 0.8618). Specific wavelengths associated with chemical and physical changes were identified, and spatial distribution maps provided real-time visualization of spoilage progression. These findings highlight the potential of HSI as a rapid, non-invasive, and cost-effective technique for real-time quality monitoring and shelf life management of BSG, supporting its broader valorization. • BSG quality degrades rapidly at 20 °C (24 h) and 35 °C (12 h) storage. • Flavor and volatile profiles shift with temperature and duration. • First-order kinetics described most degradation trends (R 2 = 0.85–0.99). • Key KEGG metabolic pathways such as pyruvate metabolism, cutin, suberine and wax biosynthesis, alpha-linolenic acid metabolism . • HSI Predictions for protein, phenol, fat, sugar, pH and color were accurate and reliable. • HSI combined with ML enables effective BSG quality monitoring during storage.