Food additive titanium dioxide (E171) alters gut microbial metabolic activity and butyrate production in the TIM-2 in vitro colon model

Aims Food-grade titanium dioxide (E171) is widely used as a food additive, yet concerns persist regarding potential gastrointestinal effects, possibly mediated by interactions with the gut microbiome. This study aimed to investigate the physicochemical behavior of E171 under different digestive contexts and to assess its effects on gut microbial composition and metabolic activity.Methods and results The dynamic in vitro colon model TIM-2 was used to expose human fecal microbiota to E171 under fasted (aqueous suspension; E171-aq) and fed (yogurt matrix; E171-yog) conditions. Particle size distribution, reactive oxygen species formation, microbiome composition (16S rRNA gene sequencing), and short-chain fatty acid production were analyzed. Larger aggregates were observed under fasted conditions (mean diameter similar to 210 nm), whereas digestion in yogurt produced smaller aggregates (mean diameter similar to 167 nm) and a higher nanoparticle fraction, reaching up to 20%. No ROS production was detected following fermentation. Both E171-aq and E171-yog significantly increased butyrate levels, indicating altered microbial metabolic activity. Microbiome profiling revealed compositional shifts, including a decreased relative abundance of Blautia and an increased relative abundance of Lachnospiraceae, taxa associated with inflammatory and metabolic responses.Conclusions E171 undergoes distinct physicochemical transformations depending on the digestive context, with enhanced nanoparticle formation under fed conditions. E171 exposure also modulates gut microbiome composition and function, notably by stimulating butyrate production.