Interactions of different hydrocolloids with milk proteins

To control rheological properties and accomplish perfect sensory properties and mouthfeel, polysaccharides are added to milk-based beverages. However, in contrast to expectations, it is often found that adding low concentrations of xanthan gum or guar gum to milk provokes phase separations of unclear physical origin. From this observation, questions arise regarding the interaction of added polysaccharides and the proteins present in milk - caseins and whey proteins. The focus of this study is to investigate such systems and to understand the basic interactions of caseins and whey proteins with different hydrocolloids. The hydrocolloids used in this study are xanthan gum, guar gum, gellan gum as well as iota-carrageenan, which were dissolved in pasteurized, non-homogenized, skimmed milk. The methods used for the examinations are light microscopy, measurement of zeta potential, atomic force microscopy and measurement of particle sizes. It was found for the case of xanthan gum dissolved in milk that the xanthan gum molecules and some of the whey proteins are found in the upper phase whereas the casein micelles as well as whey proteins are in the lower phase. For the case of guar gum dissolved in milk, the guar gum molecules are present in the upper phase and the casein micelles are present in the lower phase. This phase separation is probably caused by depletion interaction. Whey proteins are found in both phases. For the cases of iota-carrageenan, respectively, gellan gum dissolved in milk no macroscopic phase separation is observed and the measurements suggest the formation of complexes between the hydrocolloid and whey proteins.