Deformation and fracture of wheat, corn and rice starch gels in lubricated and bonded uniaxial compression

Wheat, corn and rice starch gels were prepared by heating 10% dispersions at 80°C, 94°C and 121°C for 30 min. The response of these gels in uniaxial compression was determined under both bonded and lubricated conditions up to the point of fracture. For corn and wheat starch gels the stress-strain curves in lubricated compression were relatively insensitive to gel preparation temperature. For rice starch, the modulus in lubricated compression was lower than for corn and wheat. Further, the modulus of rice starch gels decreased with increasing temperature of gel preparation. Stress at fracture for all starches was strongly dependent on preparation temperature, being highest for samples prepared at 94°C and lowest for the 80°C gels. In bonded compression, samples become barrel shaped but the elastic modulus can be corrected for this geometric effect. When this is done, the stress-strain curves for both bonded and lubricated compression agree, but stress and strain at fracture are much lower in bonded compression. Uniaxial compression measurements such as these can provide deeper insight into the ultimate properties of gels and offer a viable alternative to purely empirical methods, such as the embedded disc, for evaluating fracture behavior of gels and other soft foods.