Diffusion coefficients for losses of water soluble solids during blanching of green asparagus
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Diffusion coefficients for water soluble solid (SS) losses during blanching operation were measured for two cultivars of green asparagus (UC-72 and UC-157). Samples with 8 mm gauge diameter (measured at 100 mm from tip) and 160 mm in lenght were used in this study and were considered as infinite cylinders. Quasi-isothermal experimental conditions were achieved for application of a Fickian model for the leaching process. Experiments were performed at 65, 75, 85 and 95C with constant high stirring to eliminate surface mass transfer resistance. Tissue SS concentration was measured through time up to 600 seconds. An explicit finite difference method was used for calculating diffusion coefficients for each temperature. By a trial and error adjustment, the experimental profiles of SS concentration (kg soluble solids/kg product) were compared with those generated by the numerical model until obtaining a minimal value for the root mean square relative error (%RMSE). The %RMSE values obtained ranged from 5.72% to 7.88%. The calculated diffusion coefficients for both cultivars of asparagus ranged from 7.610-10 to 3.210-9 m2/s and the temperature dependence was fitted to an Arrhenius equation. The calculated Activation Energies (Ea) were 46.0 kJ/mol and 43.5 kJ/mol for UC-72 and UC-157 asparagus cultivars, respectively.
