Effect of a whey protein network formed by cold gelation on starch digestibility

Abstract

Composite gels of whey protein isolate (WPI) and potato starch (PS) were formed by calcium chloride induced cold gelation to obtain microstructures where native starch granules were encased in the WPI network. Gels were then subjected to heat treatment and PS gelatinized inside the protein network. In vitro starch digestibility was investigated using the INFOGEST protocol to explore if the protein gel was able to protect gelatinized starch granules from enzymatic attack during digestion. This study was focused on the impact of gel particle size and protein concentration on glucose release from the matrix. Mechanical and rheological properties of the composite gels were also evaluated after heat treatment. Glucose release from the matrix was reduced until the intestinal step of the simulated digestion when gels were ground to a particle size of ~1 mm. When gels were cut to a particle size of ~5 mm glucose release was decreased until the end of the test. In this case, at the end of the digestion glucose release was reduced by 15.5 and 20.5% for composite gels with 8 and 10% WPI respectively, whereas no significant reduction was observed for the gel with 6% WPI. Therefore, the effect of the WPI network on starch digestibility depended on particle size and on protein concentration. Mechanical and rheological properties of the gels were related to starch digestibility: PS hydrolysis rate decreased with increasing hardness and elasticity of the gels. This work contributes to a better understanding of starch digestion in soft food matrices.