Tomato phenolic extract reduces starch digestibility: potential for developing low-glycaemic starchy meals

Interactions among food components can influence nutrient digestibility and absorption. This study investigates the relationship between starch and tomato polyphenols to predict potential effects on glycaemia. Phenolic extracts were prepared from raw tomato peels and processed tomato paste, characterised using LC-MS/MS targeted metabolomics, and applied to cooked starch to measure amylolysis using an in vitro single-enzyme digestion model. Two doses of tomato-derived phenolics were tested. Polyphenols are hypothesised to reduce starch hydrolysis by forming non-covalent interactions with starch or by inhibiting the enzyme, or both. At an equal starch-to-extract ratio (25 mg), starch digestibility was reduced by 10%. At a lower extract dose (12.5 mg, half the starch weight), only the tomato paste extract significantly reduced starch digestion, suggesting a synergistic effect of multiple phenolic compounds present in the tomato paste extract. These findings highlight the potential of tomatoes to moderate postprandial glycaemia when consumed with starch-rich foods. Furthermore, the use of tomato byproducts, such as the peel, could enhance the phenolic content of tomato products, possibly amplifying their health effects.