Kinetics of thermal softening of potato tissue heated by different methods

Abstract

The kinetics of thermal softening of potato tissue heated by steaming, steaming+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 thermal softening of tissue could be described by two simultaneous first-order kinetic mechanisms. Shear rheological properties 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 steaming treatments as compared to 46% and 36%, respectively, for steaming+hot air and microwave. The loss of moisture of samples accounted for the increase in the firmness ratios, especially in steaming+hot air treatments, resulting in a potato with greater firmness but with a texture unacceptable to the consumer. Tension rheological properties and relaxed force detected the loss of moisture to a more significant degree and could therefore be considered very suitable for studying thermal treatments that involve the drying of tissues. With these heating methods, gelatinization contributes less than cell wall structure to potato tissue softening as determined either by kinetic parameters or by microscopic observations.