Impact of reduced pancreatin and bile on Fe and Zn bioaccessibility assessment using the INFOGEST in vitro digestion method with stable isotopic labelling

In a previously proposed stable isotope approach based on the INFOGEST protocol, pancreatin and bile amounts were reduced due to their high mineral content, which interferes with Fe and Zn measurements. The present study examined the impact of reagent reduction on macronutrient digestibility and, consequently, mineral release in ten food samples. Macronutrient digestibility was higher under INFOGEST conditions. However, Fe and Zn solubility were not consistently modified across matrices, although, a general trend of increased solubility was observed in the standard INFOGEST method. Fe solubility increased by 64–91 % in cereals, beans, and nuts but decreased by 48 % in sweet potato. Similarly, Zn solubility increased by 11–75 % in oats, nuts, and leafy vegetables, while it decreased by 18–64 % in potatoes and beans. Overall, the influence of enzymatic action and background minerals could not be isolated, thus standardisation of the INFOGEST method for mineral bioaccessibility assessment is urgently needed. • High mineral background in fluids interferes with Fe and Zn bioaccessibility measurements. • Reducing the amounts of pancreatin and bile in the fluids can impair protein and starch hydrolysis. • Fe and Zn solubility varied across food matrices and in vitro digestion methods. • Fe and Zn solubility tends to be higher under standard INFOGEST conditions.