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Drying of Salvia officinalis L. by hot air and microwaves: dynamic desorption isotherms, drying kinetics and biochemical quality


Salvia officinalis is an important source of antioxidants. However, few studies have carried out its postharvest treatments. Drying and antioxidants extraction form Salvia officinalis were carried out and dynamic vapor sorption technique was applied for the first time for desorption isotherms determination. Two drying processes were investigated and compared. Hot air convective drying at four temperatures (50, 60, 70 and 80 °C) and three air velocities (0.5, 1 and 1.42 m/s) and microwave drying at four output powers (18, 368, 518 and 618 W) were used for S. officinalis drying and also for analysis of their impact on polyphenols, flavonoids and antioxidant capacity. Drying kinetics were established and modeled by Page equation. Better kinetics and superior product quality were obtained by microwaves compared to hot air convective drying. Effective diffusivities were calculated and were different depending on the process. They ranged between 1.7.10−10 and 8.37.10−10 m2/s for microwaves and from 2915.10−12 and 2964.10−11 m2/s for hot air. Energy activation was 1054.85 J/mol for hot air and 4.85 W/g for microwave.

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Isotherm model parameter


Kinetic model parameter


Antioxidant capacity

aw :

Water activity (-)


Isotherm model parameter


Kinetic model parameter


Isotherm model parameter

D0 :

Arrhenius factor

De :

Effective diffusivity (m2/s)


Drying rate (s-1)

Ea :

Activation energy (J/mol or W/g)


Isotherm model parameter


Kinetic model parameter

K1 :

Isotherm model parameter

k1 :

Kinetic model parameter

K2 :

Isotherm model parameter

k2 :

Kinetic model parameter


Half thickness of the leaves (m)


Mass (kg)


Dimensionless moisture content ratio


Number of observations


Kinetic model parameter

n1 :

Isotherm model parameter

n2 :

Isotherm model parameter


Output power (W)


Universal gas constant (8.314 J/mol K)


Relative humidity (%)

R2 :

Correlation Coefficient


Sum of squares due to error


Sum of squares due to regression


Total sum of squares


Temperature (K or °C)


Time (s)


Total flavonoids content


Total polyphenols content


Air velocity (m/s)


Moisture content (kg water/kg dm)

Xm :

Isotherm model parameter

y i :

Response value

\( {\widehat{y}}_i \) :

Predicted response value

\( {\overline{y}}_i \) :

Mean response value




Dry matter




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The authors acknowledge the financial support provided by the Tunisian Minister for Higher Education.

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Correspondence to Monia Jebri.

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Jebri, M., Desmorieux, H., Maaloul, A. et al. Drying of Salvia officinalis L. by hot air and microwaves: dynamic desorption isotherms, drying kinetics and biochemical quality. Heat Mass Transfer 55, 1143–1153 (2019).

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