Effect of drying methods on drying kinetics,energy features, thermophysical andmicrostructural properties of Stevia rebaudiana leaves

Lemus-Mondaca, Roberto; Zura-Bravo, Liliana; Ah-Hen, Kong; Di Scala, Karina

Keywords: sem, thermal properties, Drying modelling, Stevia leaves, energy usage

Abstract

BACKGROUND: Stevia leaves were subjected to convective hot-air, infrared and vacuum drying at 40, 60 and 80 °C, followed by an assessment of thermophysical properties and microstructure, along with drying kinetics modelling and evaluation of energy features for all drying operations. RESULTS: Effective moisture diffusivity (Deff) showed dependency on temperature with values ranging from 1.08 × 10−12 to 7.43 × 10−12 m2 s−1 for convective drying, from 0.71 × 10−12 to 6.60 × 10−12 m2 s−1 for infrared drying, and from 1.29 × 10−12 to 5.39 × 10−12m2 s−1 for vacuum drying. The thermal properties of the dried Stevia leaves under different drying conditions showed values of density, specific heat, thermal diffusivity, thermal conductivity and thermal effusivity ranging from 95.6 to 116.2 kg m−3, 3050 to 3900 J kg−1 K−1, 4.28 × 10−7 to 5.60 × 10−7 m2 s−1, 0.16 to 0.23 W m−1 K−1 and 244 to 305 W s0.5 m−2 K−1, respectively. As for microstructure, convective hot-air drying showed better preserved leaf characteristics, compared to infrared- and vacuum-drying, whereby scanning electron microscopy (SEM) image analysis also revealed noticeable differences at higher temperatures. Statistical analysis showed that the Midilli–Kuçuk model fitted best the experimental data of drying curves (0.961 < r2 < 0.999, 0.000064 < SSE < 0.005359, and 0.000074 < χ 2 < 0.006278). Comparison of the drying methods with respect to energy features showed that convective drying at 80 °C led to lowest specific energy consumption (61.86 kW h kg−1) with highest efficiency (8.5%). CONCLUSION: The results of this study contribute to a better understanding of the drying behaviour and showed that thermophysical properties of dried Stevia leaves and energy features are affected by drying methods.

Más información

Título de la Revista: JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE
Volumen: 101
Editorial: WILEY-BLACKWELL
Fecha de publicación: 2021
Página de inicio: 6484
Página final: 6495
Idioma: Inglés
URL: https://onlinelibrary.wiley.com/doi/epdf/10.1002/jsfa.11320
DOI:

10.1002/jsfa.11320

Notas: WOs Core collection