Rheological properties of acid skim milk gels as affected by the spatial distribution of the structural elements and the interaction forces between them

Abstract

The modulus, fracture stress and fracture strain of acid-induced skim milk gels prepared from preheated skim milk that was aged for 1200 min depended strongly on pH heating. The role of gel structure regarding the effect of pH heating on gel modulus and fracture stress and strain is discussed. Milk preheated at pH 6.20 gave finer stranded gels likely containing more curved strands with probably less S–S interactions than gels from pH heating 6.90 milk. The lower stiffness of gels made from pH heating 6.20 milk could be explained by a combined effect of differences in strand curvature, gel coarseness and S–S interactions, and the lower fracture stress by a combined effect of gel coarseness and S–S interactions whereby the first effect is opposite to and overruled by that of the S–S interactions. The lower modulus and fracture stress of gels from unheated milk could be explained by a combination of strand curvature and less S–S interactions, and by less S–S interactions alone, respectively.