Structural characterization of solid lipoproteic colloid gels by ultra-small-angle X-ray scattering and the relation with sodium release

Sodium reduction in protein/lipid-based products such as cheese is becoming increasingly important to the food industry. Understanding the structure critical to sodium release is one of the keys to effectively controlling the sensory quality of the product while lowering the sodium content. In this study, ultra-small-angle X-ray scattering (USAXS), novel to food research, was used to characterize the structure of solid lipoproteic colloid (SLC) gels as a model food. The SLC gels were made via heat-induced gelation of emulsions of whey protein isolate and anhydrous milk fat. The gels varied in the contents of protein, fat, and NaCl and homogenization pressures. The gyration radii of the protein aggregates (r(g,p)) and the fat globules (r(g,f)) of the samples before and after the gelation were obtained via fitting the USAXS profiles to inspect the structure formation of the SLC gels. The effects of formulation and processing on the gel r(g,p) and the gel r(g,f) were analyzed. In addition, the gel r(g,f) and the hydrodynamic radius of the droplets (r(h,e)) in the emulsions were correlated with sodium release. The correlation suggested that gel r(g,f) is a better indicator of sodium release than the emulsion r(h,e). The findings from this study indicated that USAXS is feasible for the structural investigation of protein/lipid-based foods. (C) 2016 Elsevier Ltd. All rights reserved.