Effect of pre-cooling and freezing rate on mechanical strength of potato tissues (cv Monalisa) at freezing temperatures

A study was conducted on the effect of different freezing rates (0.5, 1.25 and 2 degrees C/min) and pre-cooling (3 degrees C for 30 min) on the mechanical strength of potato (Solanum tuberosum L.) tissues at temperatures ranging from -3 degrees C to -18 degrees C. The rheological parameters derived from compression, shearing and tension of frozen samples showed that the rheological behaviour of the tissue is directly related to the degree of structural damage. When tissue was frozen at 2 degrees C/min, the rheological parameters declined significantly within the range of -6 to -9 degrees C. Precooling caused a more linear increase in the tissue's mechanical strength, reducing the number of volumetric changes and the number of dog-bone-shaped specimens with static cracking. In this way it was possible to calculate a temperature coefficient for each rheological parameter giving the degree of loss through freezing. The highest coefficient was for apparent modulus of elasticity in tension (7.87%). For comparative purposes, this study also examined the same rheological parameters obtained between 0 and 40 degrees C. The compression test was the best test for analysis of these effects within the negative range, while the tension test was most sensitive to the effects of temperature in the positive range.