Fractional conversion technique was used on firmness change kinetics of sardine sheets during vacuum pulse osmotically dehydration at temperatures between 30 and 38 degrees C, and brine concentrations between 0.15 and 0.27 g NaCl/g. The equilibrium firmness of sardine sheets for different brine concentration and temperature were determined. The equilibrium firmness increased with increasing brine concentration as well as temperature (p < 0.05). Fraction conversion of firmness changes followed first order kinetics (R(2) > 0.90). The rate constant increased with increasing concentration as well as temperature of the osmotic solution (P < 0.05). The rate constant varied from 2.97 x 10(-3) to 2.17 x 10(-2) min(-1). The temperature dependence of the changes indicated an Arrhenius relationship (R(2) > 0.90). The activation energies varied from 21.78 to 93.42 kJ/mol when brine concentration increasing from 0.15 to 0.27 g NaCl/g. Higher activation energy (93.42 kJ/mol) indicated the greatest temperature sensitivity of firmness at 0.15 g NaCt/g. (c) 2005 Elsevier Ltd. All rights reserved.