Functional and in vitro gastric digestibility of the whey protein hydrogel loaded with nanostructured lipid carriers and gelled via citric acid-mediated crosslinking

Nanostructured lipid carriers (NLCs) with mean size of 347 nm were fabricated and added into a heat-denatured whey protein solution. The subsequent crosslinking of proteins by citric acid or CaCl₂ resulted in the formation of cold-set hydrogels. Fourier transform infrared spectroscopy (FTIR) proposed formation of more hydrogen bonds in gel due to NLC loading or citric acid-mediated gelation. It was also found based on FITR spectroscopy that citric acid crosslinking disordered whey proteins. Scanning electron microscopy (SEM) imaging showed a non-porous and finely meshed microstructure for the crosslinked gels compared to non-crosslinked counterparts. Crosslinking also increased the firmness and water-holding capacity of gels. In pepsin-free fluid, a strong correlation existed between reduction in gel swellability and digestibility over periods up to 60 min due to NLC loading and citric acid gelation. However, in peptic fluid, NLC loading and citric acid crosslinking brought about much higher decrease in digestibility than swellability.