Metabolic complementarity in LAB-yeast co-fermentation associates with enhanced ester aroma in cream cheese.

To address the limited flavor complexity of traditional cream cheese, this study systematically investigated the synergistic effects of LAB-yeast co-culture systems on its ester flavor profile. HS-SPME-GC-MS analysis revealed that among six LAB-yeast strain combinations, the K. marxianus and K. lactis co-culture was optimal, achieving total ester and alcohol contents of 71.45 μg/kg and 26.3 μg/kg, respectively; with results consistent with trends observed by E-nose and sensory evaluation. Further optimization determined 4% as the optimal total yeast inoculation level and a 1:4 (K. marxianus: K. lactis) culture broth ratio as optimal, yielding 75.6 μg/kg relative ester content and balanced flavor with acceptable texture and physiochemical properties. Fermentation dynamics revealed temporal metabolic complementarity: K. marxianus dominated ethanol synthesis, while the co-culture promoted early-phase organic acid accumulation and a late-phase shift potentially redirecting carbon flux toward ester biosynthesis. Metabolomics and KEGG pathway analysis revealed that K. lactis expanded the acetyl-CoA pool while K. marxianus generated higher alcohols, indicating a cross-feeding network potentially redirecting carbon flux from acid pathways toward acetyl-CoA synthesis and fruity ester formation. Based on metabolic complementarity, this study provides a metabolic framework for targeted ester enhancement and a clean-label technological pathway for flavor-oriented development in fermented dairy systems.