Effect of Osmotic Dehydration on Air-Drying Characteristics of Chayote

Abstract

In this study the effect of osmotic dehydration (OD) on the air-drying kinetics of chayote (Sechium edule (Jacq.) Swartz) fruits was investigated. Fresh and osmotically dehydrated chayote parallelepipeds (1 × 1 × 2 and 4 × 4 × 2 cm) were subjected to convective drying at air temperatures of 50 and 60°C, with air velocities of 1.5 and 2.5 m/s. The OD pretreatments were performed in 10 and 25% NaCl solutions (w/w) at 25°C during 3 h using a solution-to-fruit mass ratio of 4:1. The use of higher air velocities notably accelerated drying rates as manifested through significantly higher drying rate constants estimated with Page's model, whereas no effect of temperature was observed. A previously reported analytical solution that considers both product shrinkage and variable diffusivity was generalized to describe the drying kinetics of food products with parallelepiped geometry. Selected drying experiments were then fitted to this solution using six different sets of model assumptions. Results indicated that product shrinkage is the main factor to be considered in order to estimate reliable values for diffusion coefficients. The OD pretreatments produced a significant reduction of the initial moisture content of chayote slabs before drying, thus allowing shorter drying time, which may lead to reduced energy consumption.

Keywords:

• Air drying
• Chayote
• Combined drying
• Osmotic dehydration

ACKNOWLEDGMENT

The authors thank the Dirección General de Educación Superior Tecnológica (DGEST) and the Secretaría de Educación Pública (SEP) for providing financial support through Contracts 2792.09-P and PROMEP/103.5/09/4194, respectively.

Notes

^a OD = Osmotically dehydrated. Values in parentheses indicate the osmotic solute concentration (% w/w).

^a Means (±standard deviation) within a column followed by different letters are significantly different (p < 0.05).

^b When compared with fresh product.

^a Values in parentheses indicate the R ² statistics of the individual drying kinetics.

^b Values in brackets indicate the 95% CI.

^a Values in parentheses indicate the drying time differences in minutes.

^a S = sample size, P = pretreatment, v = air velocity, T = air temperature.

^a Values in parentheses indicate the 95% CI.

^b This value was intentionally reduced to produce an opposite effect of water content on moisture diffusivity.