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Sorption behavior and thermodynamic characteristics of stevia leaves as affected by freeze drying and gamma irradiation technologies

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Abstract

As a result of the growing demand for low-calorie sweeteners, interest in stevia plant has increased. Two methods are applied for the preservation of stevia leaves: freeze drying and gamma irradiation at 1 kGy. Because most studies have focused on sorption characteristics of plants, the present work aims to evaluate the effect of these two technologies on moisture sorption and thermodynamics properties of stevia leaves at 30 °C, 40 °C, and 50 °C using the static gravimetric method. The obtained results indicated that freeze-dried stevia adsorbed more water vapor. According to the adsorption results and for ensuring microbial stability during storage, the moisture content should not be higher than 10.10%, 11.58%, and 13.79% dry weight basis (d.b.) for commercial, irradiated, and freeze-dried stevia leaves, respectively. Guggenheim–Anderson–de Boer (GAB) model was fitted to the experimental data. The monolayer moisture content and the surface area of sorption were shown to decrease with increasing temperature. The isosteric heat and differential entropy of sorption were found to decrease with increasing moisture content. The optimal water activities for conservation values were determined and reported as being 0.35, 0.32, and 0.35 for commercial, freeze-dried, and irradiated stevia, respectively. Thus, this study could be used as a reference to specify the adequate storage conditions of stevia leaves.

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Data availability

The data used to support the findings of this study are available from the corresponding author upon request.

Abbreviations

X eq = EMC:

Equilibrium moisture content (% d.b.)

Am:

Area of a water molecule (1.06 × 10−19 m2)

N A :

Avogadro’s number (6 × 1026 molecules/mol)

K B :

Boltzmann constant (1.38 × 10−23 J K−1)

MRE:

Mean relative error (%)

\({\text{Xeq}}_{{\text{i,exp}}}\) :

Experiment equilibrium moisture content (% d.b.)

\(Xeq_{i,pred}\) :

Predicted equilibrium moisture content (% d.b.)

GAB:

Guggenheim–Anderson–de Boer

X m :

Monolayer moisture content

\(\Delta H_{d}\) :

Isosteric heat of sorption (kJ mol−1)

\(\Delta h_{d}\) :

Net isosteric heat of sorption (kJ mol−1)

\(\Delta S_{d}\) :

Entropy of sorption (J mol−1 K−1)

R:

Universal gas constant (8.3145 J mol−1 K−1)

aw :

Water activity

\(\theta\) :

Temperature (°C)

d.b.:

Dry weight basis

R 2 :

Coefficient of determination

N :

Number of data points

\(\varphi\) :

Spreading pressure (J m−2)

C, K, X m :

GAB model coefficients

S :

Solid surface area (m2 g−1 dry solids)

\(M_{{H_{2} O}}\) :

Molecular weight of water (18 g mol−1)

T:

Absolute temperature (K)

\(\Delta H_{vap}\) :

Heat of vaporization of water

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Acknowledgements

This study was supported by the MESRSFC and the CNRST of the Kingdom of Morocco in the priority areas of research valorization scientific and technological by innovation of local products Moroccan: aromatic and medicinal plants in IAA and ICPC (R2BINNOVA) code: PPR-B-R2BINOV-Mahrouz-FSUCA- Marrakech. The authors also would like to acknowledge MOGADOR Cooperative (ESSAOUIRA, Morocco) for kindly providing the stevia plant material.

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Authors and Affiliations

  1. SCIMATOP (LICVEDD) Laboratory of Innovation and Sustainable Development & Expertise in Green Chemistry, Department of Chemistry, Cadi Ayyad University, Marrakesh, Morocco

    Nadia Hidar, El Mustapha El Adnany, Lamyae Lahnine, Abderrahim Jaouad & Mostafa Mahrouz

  2. Department of Civil Engineering, National School of Applied Sciences (ENSA), Ibn Zohr University, Agadir, Morocco

    Abdelhamid Noufid

  3. Team of Solar Energy and Medicinal Plants, Teacher’s Training College, Cadi Ayyad University, Marrakesh, Morocco

    Ali Idlimam

  4. Unité de Recherche sur les Techniques Nucléaires l’Environnement et la Qualité (URTNEQ), Centre Régional de la Recherche Agronomique de Tanger, 78 Bd sidi Med ben abdellah, 90000, Tanger, Morocco

    Mohammed Mouhib

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  1. Nadia Hidar
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  2. Abdelhamid Noufid
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  3. El Mustapha El Adnany
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  7. Abderrahim Jaouad
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  8. Mostafa Mahrouz
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Correspondence to Nadia Hidar.

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Responsible Editor: Ksibi Mohamed.

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Hidar, N., Noufid, A., El Adnany, E.M. et al. Sorption behavior and thermodynamic characteristics of stevia leaves as affected by freeze drying and gamma irradiation technologies. Euro-Mediterr J Environ Integr 8, 179–189 (2023). https://doi.org/10.1007/s41207-023-00346-6

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  • DOI: https://doi.org/10.1007/s41207-023-00346-6

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