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

The formation of a casein gel by gradual acidification is the basis for pro ducing fermented dairy products. Caseins mainly contribute to the developme nt and stability of texture that are specific for each product. The composi tion and technology of producing casein gels affect those texture propertie s that are based on the microstructure of the products. The aim of the pres ent study was to establish the connections existing between texture propert ies and the microstructure of milk-based acid gels under various conditions . The concentration of minerals, e.g. NaCl, was set to varying amounts prio r to acidification in order to examine the effect on casein aggregation. Fu rthermore, the influence of rennet action and pH on gel properties was dete rmined. The addition of NaCl to milk leads to an enhanced serum-holding capacity an d decreased viscosity of casein gels. This phenomenon is attributed to the lower tendency of casein micelles to aggregate as observed by electron micr oscopy. The influence of minerals can be eliminated by adding rennet or low ering the pH down to 3.5 since these measures reduce the number of the char ged sites on casein micelle surfaces. The serum-holding capacity and viscos ity 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 compa ct at pH 3.5 and incorporate more serum than those at pH 4.6. (C) 1999 Publ ished by Elsevier Science Ltd. All rights reserved.