Water diffusivity and mechanical changes during hazelnut hydration

The hydration kinetics of hazelnut at 25 degrees C were studied using a Fic kian approach. Results from a puncture test on the newly-hydrated (NHH) and self-equilibrated (EH) hazelnuts, with different hydration levels were als o analyzed in order to determine the critical water content (CWC) of the pr oduct. Changes in the mechanical response of hazelnut with a water content greater than 9.3 g water/100 g product allowed the CWC value to be establis hed at this hydration level. The force-deformation curves of the NHH sample s appeared different from those of the EH samples for the same hydration ti me, thus implying that water concentration profiles affect the mechanical r esponse. The water profiles deduced from a Fickian approach (taken into acc ount the "effective" diffusivity obtained: 2.46 x 10(-10) m's) were in agre ement with the mechanical differences. (C) 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reser ved.