Mathematical Modeling of Moisture Sorption Isotherms and Determination of Isosteric Heats of Sorption ofZiziphusLeaves

Amel Saad,Boufeldja Tabti,Belkacem Draoui,Boumediene Touati,Asma Abdenebi,Said Benaceur

doi:10.1155/2014/427842

Abstract

Desorption and adsorption equilibrium moisture isotherms ofZiziphus spina-christileaves were determined using the gravimetric-static method at 30, 40, and 50°C for water activity(aw)ranging from 0.057 to 0.898. At a givenaw, the results show that the moisture content decreases with increasing temperature. A hysteresis effect was observed. The experimental data of sorption were fitted by eight models (GAB, BET, Henderson-Thompson, modified-Chung Pfost, Halsey, Oswin, Peleg, and Adam and Shove). After evaluating the models according to several criteria, the Peleg and Oswin models were found to be the most suitable for describing the sorption curves. The net isosteric heats of desorption and adsorption ofZiziphus spina-christileaves were calculated by applying the Clausius-Clapeyron equation to the sorption isotherms and an expression for predicting these thermodynamic properties was given.

Highlights

Ziziphus spina-christi (L.) Desf. is a multipurpose tree species belonging to the botanical family Rhamnaceae [1]; it grows wild in Asia and tropical Africa
Several empirical and semiempirical equations have been proposed for the correlation of the equilibrium moisture content with the water activity of food products
The values of constants of the eight models, that is, GAB, BET, Handerson-Thompson, modified Chung and Pfost, Halsey, Oswin, Peleg, and Adam and Shove, fitted to the desorption and adsorption data along with their standard error (S), the correlation coefficient (r), and the percent average relative deviation (P) for the studied temperatures are given. These results indicate that all the models are acceptable for predicting the equilibrium moisture content

Summary

Introduction

Ziziphus spina-christi (L.) Desf. is a multipurpose tree species belonging to the botanical family Rhamnaceae [1]; it grows wild in Asia and tropical Africa. People from Algerian Sahara use different parts from Ziziphus spina-christi to treat several ailments, such as abdominal pains, diarrhea, lips herpes, fever, diabetes, sores, and burns [26,27,28]. Water activity has long been considered as one of the most important quality factors especially for long-term storage;it affects the shelf-life, safety, texture, flavor, and smell of foods. Several empirical and semiempirical equations have been proposed for the correlation of the equilibrium moisture content with the water activity of food products. The object of this research is to obtain experimental equilibrium moisture isotherms for Ziziphus spina-christi leaves at 30, 40, and 50∘C, determine the most suitable model describing the isotherms, determine hysteresis phenomena, and calculate the isosteric heat as a function of moisture content

Materials and Methods

Data Analysis

Results and Discussion

Conclusion

Conflict of Interests