Effect of minerals and pH on rheological properties and syneresis of milk-based acid gels

Abstract

The formation of a casein gel by gradual acidification is the basis for producing fermented dairy products. Caseins mainly contribute to the development and stability of texture that are specific for each product. The composition and technology of producing casein gels affect those texture properties that are based on the microstructure of the products. The aim of the present study was to establish the connections existing between texture properties and the microstructure of milk-based acid gels under various conditions. The concentration of minerals, e.g. NaCl, was set to varying amounts prior to acidification in order to examine the effect on casein aggregation. Furthermore, the influence of rennet action and pH on gel properties was determined. The addition of NaCl to milk leads to an enhanced serum-holding capacity and decreased viscosity of casein gels. This phenomenon is attributed to the lower tendency of casein micelles to aggregate as observed by electron microscopy. The influence of minerals can be eliminated by adding rennet or lowering the pH down to 3.5 since these measures reduce the number of the charged sites on casein micelle surfaces. The serum-holding capacity and viscosity of casein gels is higher, if the pH is set to 3.5 instead of pH 4.6. It was concluded from electron microscopy that the gel strands are less compact at pH 3.5 and incorporate more serum than those at pH 4.6.