FIQT

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, hfp, 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 hfp, fluctuated between 480 and 1950 W m−2 °C−1. The highest hfp 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 hfp 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.

Using Response Surface Methodology the effects of NaOH concentration (4–20%), process temperature (55–95°C) and time (1–7 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, 11–13%, 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.