Effects of inulin/oligofructose on the thermal stability and acid-induced gelation of soy proteins

Differential scanning calorimetry (DSC) and dynamic oscillatory shear testing were performed to study the influence of inulin (Raftiline® HP-gel and Raftiline® ST-gel) and oligofructose (Raftilose® P95) on the thermal stability and gelation (using glucono-δ-lactone [GDL] as a coagulant) of soy protein isolate (SPI) dispersions. Addition of 10% (w/v) inulin/oligofructose or sucrose increased (P < 0.05) the peak denaturation temperatures (T_m) of 7S and 11S soy proteins in SPI dispersion (5% [w/v], pH 7.0) by an average of 1.9 and 2.3°C, respectively. GDL induced SPI thermal gelation, and the gel rheology was affected by both the pH decline and the specific temperature of heating. Addition of inulin/oligofructose (8%, w/v) improved the gelling properties of preheated SPI dispersion (8%, w/v) coagulated with GDL, showing 14.4 to 45.6% increase (P < 0.05) in gel rigidity (G′ value) at the end of heating (81°C). Microstructural examination revealed a denser protein cross-linking structure and reduced pore sizes in SPI gels containing inulin/oligofructose. In general, inulin was more capable of improving SPI gelation than oligofructose, suggesting that the degree of fructose polymerization in the fructans was of thermal and rheological importance.