ERRORS IN BLANCHING CALCULATIONS CAUSED BY USING ONE COMMON VALUE OF THERMAL-DIFFUSIVITY FOR DIFFERENT VEGETABLES

The errors in calculations of blanching time and enzyme inactivation ( decimal reduction time) when one common value of thermal diffusivity i s adopted for all vegetables are considered. Different rates of heat t ransfer (negligible heat transfer resistance and blanching in water by natural convection), food size, decimal reduction time of the enzyme (D), and reciprocal slope of the log D vs. temperature curve (paramete r z), were analysed. These variables influenced the blanching time mor e than the thermal diffusivity and consequently, for many industrial s ituations, a single thermal diffusivity value of 1.5 x 10(-7) m2 s-1 c ould be used without causing significant errors in blanching calculati ons.