Matrix-driven modulation of starch structure, digestibility, and glycemic response by brewer's spent grain in bread, cookies, and pasta
Academic Article in Scopus
Brewer's spent grain (BSG) is a major by-product of the brewing industry and represents a sustainable source of dietary fiber, protein, and bioactive compounds. This study evaluated the impact of incorporating BSG, with and without hop residues, at 5, 15, and 25% substitution levels on starch structure, in vitro digestibility, and predicted glycemic index (pGI) in bread, cookies, and pasta. BSG enrichment increased protein content by up to ~27% and total dietary fiber up to ~15%, while reducing available starch by approximately 20-30% compared with control formulations. These compositional changes induced structural reorganization of starch, reflected by increases in gelatinization peak temperature (from ~60 to 61 °C in controls to ~64-66 °C at 25% BSG), gelatinization enthalpy (¿H increased from ~5.3 to ~7.8 J g¿1 in bread), and crystallinity (from ~23% in control bread to ~32% at 25% BSG). As a result, starch digestibility shifted markedly from rapidly digestible starch (RDS) toward slowly digestible starch (SDS) and resistant starch (RS). RDS decreased by up to ~20 percentage points, while RS increased from ~4% to ~9% in bread and from ~2% to ~14% in pasta at the highest substitution level. These changes translated into a significant reduction in pGI, particularly in cookies and pasta, where values decreased from ~104 to ~61 and from ~84 to ~73, respectively. The presence of hop residues further reduced starch hydrolysis, likely due to synergistic effects of organic acids and polyphenols on digestive enzyme activity. Multivariate analyses confirmed strong associations between starch crystallinity, thermal stability, and digestion kinetics. Overall, these findings demonstrate that BSG fortification modulates starch digestibility primarily through matrix-driven structural mechanisms, with hop-derived compounds providing an additional inhibitory effect, supporting BSG as a functional and sustainable ingredient for cereal-based foods with improved glycemic response.
