Rheological properties of rennet-induced milk gels made from milk protein concentrate solutions with different ratios of As-:β-casein.

The rheological properties of rennet-induced milk gels made from milk protein concentrate (MPC) solutions with αs- (i.e., αs1- + αs2-):β-casein ratios of 1.00:0.80 (MPC A), 1.00:0.70 (MPC B) or 1.00:0.87 (MPC C), each having identical concentrations of total casein (2.5%), were studied using dynamic low amplitude oscillatory rheometry. The ratio of αs-:β-casein had no significant (P > 0.05) effect on rennet coagulation time. Storage modulus (G'; index of firmness), measured 30 min after addition of rennet, decreased with increasing ratio of αs-:β-casein. Storage modulus for gels made using each of the three MPC solutions reached plateau values ~200 min after addition of rennet, with the plateau value of G' decreasing significantly (P < 0.05) as relative concentration of β-casein increased in the MPC solutions. There were no significant (P > 0.05) differences in the frequency dependence of G' in the frequency range 0.001 to 1 Hz between gels made using any of the three MPC solutions. On shearing the gels at a rate of 0.01 s-1, the value for apparent yield stress and apparent yield strain increased significantly (P < 0.05) as relative concentration of αs-casein increased in the MPC solutions. Thus, the ratio of αs-:β-casein influenced the small and large deformation rheological properties of rennet-induced milk gels. [ABSTRACT FROM AUTHOR]