Coagulation of model infant formulae: Impact on their in vitro dynamic gastric digestion

Abstract

The rheological properties and the in vitro dynamic gastric digestion behaviours of model infant formulae containing various ratios of casein to whey protein (0:100, 40:60, 60:40 and 80:20) were investigated using a rheometer and an infant human gastric simulator. The pH profiles and the viscoelastic moduli were determined during acidification by glucono-δ-lactone and at different pepsin concentrations (0, 0.3, 1.0, 1.7 and 2.5 U/mL). The infant formula containing whey protein only formed a weak gel at about pH 5. In the presence of pepsin, all casein-containing infant formulae formed gels at pH ∼6.0 and only low pepsin activity (>0.3 U/mL) was required for the gelation. The strength of the gel/coagulum was dependent mainly on the casein content. Coagulation of protein and flocculation of oil droplets, induced by both pepsin proteolysis and the low pH under gastric conditions, were observed in the infant formulae during dynamic digestion in the human gastric simulator. Confocal images showed that the infant formula containing whey protein only formed smaller flocs of aggregated protein and oil droplets, which may have led to their observed faster protein digestion, than the infant formulae containing a combination of casein and whey protein. The casein-dominant infant formulae had greater aggregation than the whey-protein-dominant infant formulae during gastric digestion, which led to their lower rate of casein digestion. These results suggest that the extent of coagulation and the gastric digestion of the proteins in infant formulae can be controlled by the rational selection of the protein components and the ratio of casein to whey protein, such that different nutritional requirements of infants can be met.