Rheological characterization of kappa-carrageenan soy milk gels

Soy-milk gels were characterized by their uniaxial compression, stress relaxation and degree of elasticity. Their stress at failure was 19.3-23.1 kPa in the pH range of 5.4-6.4. Significant differences were found for gels at the lower pH values of 4.4-5.0. Maximum stress at failure was achieved for soy milk gels in the pH range of 5.2-6.2. At pH 5.2 there was a significant increase in the gel's stress at failure compared with lower pH. The gel deformability modulus increased from 17.5 kPa at pH 6.4 to 54 kPa at pH 5.2, then decreased to 11.2 kPa at pH 4.4. Hencky's strain at failure was also dependent on pH and decreased from 0.65-0.67 at pH values of 6.2-6.4 to 0.28 at pH 4.4. Soymilk gels became more brittle when the pH of the system decreased Results (strength, strain at failure and deformability modulus) were compared with systems of cow's milk and water gels. Gels produced at pH 5.2 were chosen for the stress relaxation and elasticity tests. Relaxation curves at five strain levels were normalized and linearized. k(1) and k(2), the constants of Peleg's model, and E-A were calculated. I;rom the calculated recoverable work and results of mechanical testing, conclusions on the character of the gel were derived. A hypothesis on the relationships between recoverable work and the asymptotic modulus is also proposed. Weight losses of soy milk gels during compression, stress relaxation and elasticity determinations were recorded and an explanation for this phenomenon is proposed. A description of soy milk rc-carrageenan gel formation is proposed and the possible role of aspargyl and glutamyl residues is described.