Digestion and matrix interactions drive phenolic compounds transformation in tomato sauce formulations

This study investigated the digestive fate of tomato phenolics and how processing and matrix interactions influence their release, transformation, and partitioning during digestion. Conventional tomato sauce, pomace-enriched sauce, and the enriched sauce co-digested with boiled rice underwent in vitro digestion (INFOGEST 2.0). Phenolic compounds were profiled in soluble and insoluble fractions across oral, gastric, and intestinal phases using untargeted and targeted LC-MS. Pomace enrichment did not significantly increase total phenolic concentration compared with conventional sauce. Digestion induced compound-specific transformations, including the breakdown of complex caffeoylquinic acids and dynamic redistribution between soluble and insoluble fractions. Co-digestion with rice modified phenolic partitioning in a compound-dependent manner, generally reducing soluble phenolic concentrations while increasing glycosylated flavonoids such as quercetin 3-β-D-glucoside. Digestion phase was the dominant driver of phenolic behaviour, while matrix composition modulated the direction of these changes through phase-dependent interactions. These findings suggest that phenolic accessibility during digestion depends not only on initial phenolic composition but also on matrix-dependent retention and release mechanisms. Overall, this study provides new insight into the digestion-dependent behaviour of tomato phenolics and quantifies compound-specific changes, highlighting the importance of matrix structure and meal composition when designing tomato by-product-enriched foods with improved phenolic delivery.