The rebodying of stirred yoghurt: interactions between proteins

The aim of the present study was to identify the nature of bonds established between protein particles after stirring that are responsible for the texture improvement of stirred yoghurts, called rebodying. Using a constant model yoghurt at pH 4·4, the effects of changes in the physicochemical conditions at stirring were studied on the subsequent rebodying. Short term rebodying was measured as the changes in viscoelastic properties at 4°C during 20 h after stirring, while long-term rebodying was measured as the viscosity changes during 28 d storage at 4°C. Moreover, stirred gels obtained from either set gels that were allowed time or not for ionic equilibration were compared. Increasing or decreasing ionic strength did not change the properties of stirred gels. Calcium chloride addition significantly decreased G′0 h, G′20 h and tan20 h but did not induce changes in the gel microstructure as observed by confocal scanning microscopy. Yoghurt rebodying could not be explained by fulfilling ionic equilibrium. Moreover, N-ethyl maleimide addition had no effect on the stirred yoghurt. Attractive electrostatic and disulphide interactions were not involved in the gel rebodying and increasing calcium concentration in the set gel limited rebodying.