Drying Characteristics, Sorption Isotherms, and Lycopene Retention of Tomato Pulp

Abstract

Tomato pulp separated by centrifugation of crushed tomatoes was dried in cabinet, tray, fluidized-bed, and freeze dryers at 50–70°C using 4–12 kgm⁻² tray loads. Drying behavior was well described by the Page's model with coefficient of determination greater than 0.99 and standard error of 0.004–0.019. A fluidized-bed dryer was more efficient to dry tomato pulp than tray, freeze, and cabinet dryers. Retention of lycopene in tomato pulp was maximum in a freeze dryer (72.483–78.093 mg 100 g⁻¹) followed by fluidized-bed (42.273–57.926 mg 100 g⁻¹), cabinet (35.532–49.271 mg 100 g⁻¹) and tray dryer (24.454–45.842 mg 100 g⁻¹) under experimental conditions (tray load 4–12 kgm⁻², temperature 50–70°C). The moisture sorption isotherms of tomato pulp obtained by equilibrating saturated salts solution of known water activity (0.113–0.92) at 30–60°C were sigmoid. A modified Henderson model was the best model for the tomato pulp with coefficient of determination more than 0.99 and standard error less than 0.270. The net isosteric heat of sorption, estimated using the Clausius-Clapeyron equation, was 21.451–5.541 Jmol⁻¹ at 25–5% moisture content (dry basis).

Keywords:

• Drying
• Page's model
• Sorption isotherms
• Sorption models
• Tomato pulp
• Water activity

Notes

R²: Coefficient of determination.

S.E.: Standard error.

*Condenser temperature.

R²: Coefficient of determination.

m is equilibrium moisture content (% dry basis); a_w is water activity; A, B, and C are coefficients; t is temperature (°C).

R²: Coefficient of determination.

S.E.: Standard error.