Combined confocal microscopy and large deformation analysis of emulsion filled gels and stirred acid milk gels

Abstract

Abstract The microstructural breakdown properties of heat-induced whey protein (WP) gels prepared at pH 7.0 or 5.4 and containing emulsified sunflower oil (7%, w/w) were studied using notch propagation tensile testing in combination with dynamic confocal laser scanning microscopy (CLSM). In addition, the microstructural breakdown properties of stirred acid milk gels containing added emulsified oil (0–15%, w/w) or Konjac glucomannan (0.05%, w/w) were studied using compressive rheological deformation in combination with dynamic CLSM imaging. The structural breakdown properties (Young's modulus and stress/strain at fracture), the microstuctural behaviour of the protein phase, the emulsified oil phase and the pattern of notch propagation during large deformation tensile testing of the WP emulsion filled gel prepared at pH 7.0 (fine stranded gel) differed from that of the WP emulsion filled gel prepared at pH 5.4 (particulate gel). The protein aggregates, emulsified oil droplets and the Konjac phase in the stirred acid milk gels flowed on compression; however, the flow pattern changed from “frictional” flow with no emulsified oil or Konjac to “slip” flow in the presence of emulsified oil or Konjac. Also, compression of stirred acid milk gels below a certain critical height led to disintegration of the aggregated protein structure, serum release and reduced stability of the oil droplets in the stirred gels. The critical compression height was influenced by emulsified oil level and the presence of added Konjac.