Gastric and Gastrointestinal Digestion of Infant Formula in the Presence of Polypropylene Nanoplastics

Polypropylene nanoplastics (nPP) have been identified as potential contaminants in infant formula, primarily due to their presence in polypropylene feeding bottles, which expose infants to nPP. Health impacts of nanoplastics exposure are not well understood. Furthermore, the effect of nPP on the digestion of proteins, which are crucial for the growth and development of infants remain unknown. Therefore, the current study investigated the in vitro digestion of infant formula proteins (1 mg/mL) with or without agglomerated nPP (10, 50 and 100 µg/mL) in simulated gastric and intestinal fluids using the infant model of digestion. Firstly, the particle size distribution of nPP and their mixture with infant formula in the simulated digestive fluids was determined. Then, the simulated in vitro gastric and intestinal digestion of the infant formula proteins was done at 37 °C and monitored during physiologically relevant period. The profiles of the digested proteins were analyzed using the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Our results suggest agglomeration on nPPs and infant formula proteins. Furthermore, caseins were digested more rapidly than whey proteins in all samples, regardless of the presence of agglomerated nPP. Meanwhile, in the presence of agglomerated nPP, the rate of digestion of allergic proteins such as β-lactoglobulin could be decreased during gastric digestion of the infant formula. During intestinal digestion of the infant formula, nearly all types of proteins were digested for all the investigated times of digestion and no differences were observed with varying concentrations of nPP. Our results suggest that nPP interacts with infant formula proteins and formed large size aggregates. Gastric and intestinal digestion of proteins is not affected significantly by the presence of nPP.