Optimization of stepwise blanching of frozen-thawed potato tissues (cv. Monalisa)

Response surface methodology was used to compare the effect of temperature and time of the first step of blanching on compression, shear, tension and stress-relaxation parameters of frozen-thawed potato tissues. A central, composite rotatable design was used to study the effects of variation in levels of temperature (52.93-67.07 degrees C) and time (15.86-44.14 min) on rheological parameters. Blanching temperature was the most important factor affecting the mechanical properties tested. The models fitted for the apparent modulus of elasticity in compression, maximum tension force, and relaxed force in the first cycle (F-r1); all had R-2>0.85 (P less than or equal to 0.01) and were used for doing predictions. Optimum conditions were with in the ranges of temperature (60-65 degrees C) and time (25-35 min) used for each factor. In the experimental verification of the models at 65 degrees C during 30 min, the lowest percentage residual between experimental and predicted values was obtained for F-r1 (0.644), which was therefore the most appropiate parameter for detecting the firming effect that the pectinesterase activity produced on frozen potato tissues as a consequence of stepwise blanching under these conditions.