Characterization of isotherms and thin-layer drying of red kidney beans, Part I: Choosing appropriate empirical and semitheoretical models

ABSTRACT

Desorption and adsorption isotherms and drying characteristics of red kidney beans were studied using static and dynamic methods, respectively. The desorption and adsorption isotherms were determined at 60, 50, 40, 30, 20, and 10°C with 32–91% relative humidity (RH). The constant RHs were generated using six saturated salt solutions at constant temperatures. The drying characteristics were determined using a thin-layer dryer with drying air at 50, 40, and 30°C with 35 and 50% RH. The dimensions of the kidney beans before and after drying were measured and shrinkage and sphericity of the beans were calculated. A new method to evaluate the best-fitted equation to characterize the thin-layer drying data was developed. The best-fitted equations to describe the desorption and adsorption isotherms were the modified Chung–Pfost and modified Guggenheim–Anderson–deBoer. The red kidney beans only experienced a falling rate drying period and had a largest shrinkage in the length direction during drying. The Henderson and Pabis model and the modified Page model were the best-fitted models to describe the thin-layer drying data. Using only the values of R² and mean squared error to evaluate the semitheoretical and empirical models might not be enough. The method developed in this study could help develop a semitheoretical or empirical model with a higher accuracy of drying constant, which could be used to estimate the effective water diffusivity.

KEYWORDS:

• Best-fitted equation
• desorption and adsorption isotherms
• drying rate
• mathematical model
• thin-layer drying

Additional information

Funding

The authors thank the Natural Sciences and Engineering Research Council of Canada for partial funding of this study as well as the Canada Foundation for Innovation, the Manitoba Research Innovation Fund, and several other partners for creating the research infrastructure. The authors are grateful to Blanche Leroy and Julien Imbs (internship students from France), Darsana Divagar (Graduated Student, University of Manitoba), Collin Demianyk (Biologist, Agriculture, and Agri-Food Canada) for technical assistance.