Sorption Isotherms and Drying Characteristics of Tomato Peel Isolated from Tomato Pomace

Abstract

Tomato peel was separated from pomace by sedimentation and dried in cabinet and fluidized-bed dryer at 50–70°C using 4–12 kg/m²tray load. The drying of tomato peel took place under the falling rate period and the drying behavior was well described by Page's model with coefficient of determination greater than 0.99 and standard error of 0.003–0.016. A fluidized-bed dryer was much more efficient than a cabinet dryer to dry tomato peel. The moisture adsorption isotherms of tomato peel were obtained by equilibrating above saturated salt solutions of known a _w (0.113–0.92) at 20–60°C. The data were analyzed using fifteen sorption models based on coefficient of determination, standard error, and residual plots. Modified Henderson was the best model for tomato peel with coefficient of determination >0.99, standard error <0.210, and a scattered residual plot. The net isostearic heat of sorption, estimated using the Clausius-Clapeyron equation, was 0.74–23.23 kJ/mol at 2.0–2.5% moisture content (dry basis).

Keywords:

• Drying
• Equilibrium moisture content
• Page's model
• Sorption isotherms
• Sorption models
• Tomato peel

Notes

Where m – equilibrium moisture content (% dry basis); a_w – water activity; C′ = C exp (h₁/RT); K′ = K exp(h₂/RT); A, B, C, K, h₁, and h₂ – coefficients; t – temperature (°C); T – Temperature (K); R – universal gas constant (J · mol⁻¹K⁻¹).