Urea supplementation is associated with holistic changes in suprathreshold non-volatile flavour perception through oral microbiome carbon metabolism.

Urea is a small inorganic compound, readily available in saliva, that can be metabolised by the oral microbiome. We hypothesised that dietary supplementation with urea would increase salivary levels, alter microbial metabolism and, potentially, modify suprathreshold non-volatile flavour perception. A semi-trained panel of 20 participants completed taste evaluations using visual analogue scales for nine tastants, both before and during a 5-day urea supplementation regimen. System-level analysis revealed a significant shift in suprathreshold non-volatile flavour perception during supplementation (PERMANOVA, p = 0.008) even though none of the nine tastants showed significant changes (p > 0.05 or an absolute percentage change greater than 10%) during the intervention. Functional gene completeness analysis, together with 13C NMR, suggested that the oral microbiome primarily utilises carbon dioxide generated from urease-mediated urea metabolism. Overall, urea supplementation was associated with changes in microbiome carbon-related metabolic pathways and induce holistic level changes in suprathreshold non-volatile flavour perception.