Interaction between Maillard reaction products and phenolics in brewer's spent grain: Structural and antioxidant insights

Abstract

Brewers' spent grain (BSG), the main lignocellulosic by-product of the brewing industry, has attracted increasing interest as a sustainable source of bioactive compounds, particularly phenolics and Maillard reaction products (MRP) such as melanoidins. Despite their health-related properties, the structural features and mechanisms underlying the bioactivity of BSG-derived melanoidins remain poorly understood. Therefore, the present study investigated the structure of melanoidins from light and dark BSG and their interactions with phenolic compounds. Dark BSG exhibited a higher degree of Maillard reaction development, though melanoidins from both types showed major molecular weight peaks at ∼19.3 and 7.9 kDa. High molecular weight melanoidins (>12 kDa) were mainly composed of carbohydrates and proteins, with 4.1–6.7 % phenolics a negative surface charge (−23.77 to −38.7 mV) and antioxidant activity. FTIR analysis revealed α-glycosidic and proteinaceous structures, the latter partially degraded by roasting. UPLC-MS/MS identified furanose-derived MR markers present in comparable proportions in the melanoidins from both light and dark BSG. Besides, results suggest that phenolics, such as ferulic acid, were covalently bound to the melanoidin matrix. Finally, the antioxidant activity of the soluble BSG fraction was associated with the presence of Maillard products, while the antioxidant capacity of the bound fraction was better related to the phenolics of BSG. Overall, these findings highlight the structural role of phenolics in modulating melanoidin properties and their contribution to antioxidant potential. Moreover, these findings provide new insights into the structural interactions between MRP and phenolics and may guide the development of improved analytical approaches for studying melanoidin–phenolic complexes.