Kinetics of thermal softening of potato tissue heated by different methods

The kinetics of thermal softening of potato tissue heated by steaming, stea ming + hot air and microwave exposure were evaluated using the rheological properties from four objective methods as firmness indicators. In the three heat treatments, the rate of ther mal softening of tissue could be describ ed by two simultaneous first-order kinetic mechanisms. Shear rheological pr operties were best for studying softening of the tissue with these methods on the basis of chemical kinetic theory. A comparison of kinetic parameters showed that steaming produced a greater degree of softening than the other two heating methods used. The firmness ratios for shear force showed that approximately: 16% of the firmness of fresh potato is retained after steami ng treatments as compared to 46% and 36%, respectively, for steaming + hot air and microwave. The loss of moisture of samples accounted for the increa se in the firmness ratios, especially in steaming + hot air treatments, res ulting in a potato with greater firmness but with a texture unacceptable to the consumer. Tension rheological properties and relaxed force detected th e loss of moisture to a more significant degree and could therefore be cons idered very suitable for studying thermal treatments that involve the dryin g of tissues. With these heating methods, gelatinization contributes less t han cell wall structure to potato tissue softening as determined either by kinetic parameters or by microscopic observations.