Using Response Surface Methodology the effects of NaOH concentration (4-20%), process temperature (55-95°C) and time (l-7 min) was determined on the yield, peeling quality, unpeeled skin and total usage of NaOH. Also evaluated were titratable NaOH in the potato tissue, NaOH penetration and "heat ring" depths during one stage chemical peeling of potatoes (Huincul variety). The best peeling quality, maximum yield and minimum total usage of NaOH was obtained for the following ranges: concentration, ll-13%, time 5-5.70 min and temperature, 90-95°C. The maximum temperature for which the "heat ring" and NaOH penetration depths were equal was 72°C where, at 20% NaOH and 7 min, peeling quality was very good and "heat ring" was absent.

The effect of temperature (110, 120 and 130°C), rotation speed (5, 10 and 15 r.p.m.) and headspace (4, 8 and 12 mm) on heat transfer coefficients to canned green peas during end-over-end sterilisation was studied using response surface methodology. The models developed for fluid-to-particle heat transfer coefficient, h fp , and overall heat transfer coefficient, U, were adequate, showing no significant lack of fit and satisfactory correlation coefficients. For the two responses, temperature, rotation speed and headspace have a significant effect. U, ranged between 477 and 905 W m )2°C)1 , while h fp , fluctuated between 480 and 1950 W m )2°C)1 . The highest h fp and U values are obtained at high temperatures, rotation speeds and headspaces. The verification of the prediction models was satisfactory. Dimensionless correlations were developed for h fp and U, with equations showing a good agreement with the experimental data. Heat transfer to liquids and particles was modelled using the Reynolds number, the Prandtl number and adimensional headspace.

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Summary Kinetic parameters describing lipoxygenase inactivation during heating of cut green beans were determined using two unsteady‐state procedures. The model used an analytical solution for heat conduction in a finite cylinder to predict time–temperature profiles, and a trial and error and a non‐linear regression of experimental lipoxygenase retentions to estimate kinetic parameters. Thermal diffusivity and convective heat transfer coefficient were determined experimentally, but thermal conductivity was estimated. Mean values obtained, with standard deviations between parenthesis, were k76°C=27.2 (9.4) s–1; k82°C=92.9 (7.5) s–1; k88°C=212.1 (52.7) s–1; k94°C=407.8 (56.7) s–1; Ea=160.7 (8.1) KJ mol−1 using the trial and error procedure; k85°C=150 (26.3) s–1 and Ea=164 (4.7) KJ mol−1 using the non‐linear regression method. Predicted and observed lipoxygenase retentions showed good agreement.