Dynamic changes of volatile compounds during coffee-grounds beer fermentation with different yeast strains: An integrated HS-SPME-GC/MS, electronic tongue and electronic nose analysis

As a major coffee processing byproduct, spent coffee grounds (SCG) contain abundant bioactive compounds despite being typically discarded. This study analyzed flavor changes in coffee-grounds beer fermented with four yeast strains (Lalvin R2™ (R),Lalvin EC1118™ (E)，Lalvin ICVD254R(D)，Uvaferm43R(U)) through an integrated multi-omics approach. Electronic tongue and nose analyses revealed distinct bitter, umami, and sulfurous notes, with Strain E showed the most balanced sensory profile. HS-SPME-GC–MS analysis detected 460 volatile compounds, showing increasing trends during fermentation. Nine key aroma-active compounds (ROAV>1) were characterized, including ethyl butyrate, guaiacol, and 2,3-diethyl-5-methylpyrazine. Notably, guaiacol contribution decreased markedly in late fermentation with strains U and D, may indicate potential time-strain synergistic effects. Metabolic trajectory analysis revealed distinct pathways among the yeast strains: Strain R favored phenolic-ester-heterocyclic compounds, Strain E predominantly produced ester‑sulfur-heterocyclics, Strain U formed aromatic aldehydes via phenylalanine metabolism, and Strain D showed acid-ester‑sulfur conversion.Yeast selection and fermentation duration significantly influenced physicochemical properties. These findings provide new insights for valorizing coffee processing byproducts.