Effect of continuous and intermittent ultrasound on drying time and effective diffusivity during convective drying of apple and red bell pepper

► A screen was successfully tested as sound transmitting surface in ultrasound-assisted convective drying of food. ► Modeling the drying curves with the Midilli model resulted in the best fit among eight mathematical models. ► Drying time savings of 23% (red bell pepper) and 27% (apple) were calcula...

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Bibliographic Details
Published in:Journal of food engineering 2012-01, Vol.108 (1), p.103-110
Main Authors: Schössler, Katharina, Jäger, Henry, Knorr, Dietrich
Format: Article
Language:English
Subjects:
Apple
Biological and medical sciences
Continuous and intermittent ultrasound
Convective drying
Food engineering
Food industries
Fruit and vegetable industries
Fundamental and applied biological sciences. Psychology
General aspects
Malus
Red bell pepper
Screen
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Summary:► A screen was successfully tested as sound transmitting surface in ultrasound-assisted convective drying of food. ► Modeling the drying curves with the Midilli model resulted in the best fit among eight mathematical models. ► Drying time savings of 23% (red bell pepper) and 27% (apple) were calculated for continuous ultrasound. ► Intermittent ultrasound at 50% net sonication time resulted in drying time savings of 18% in apple drying. ► Ultrasound had an influence on the diffusion coefficients and the length of the falling rate periods. A new approach of ultrasound-assisted convective drying was tested in this study using a screen as product support and sound transmitting surface. Red bell pepper and apple cubes were dried at 70°C in a laboratory scale hot-air drying oven. In addition to continuous ultrasound used for both products, intermittent ultrasound was applied for apple drying reducing net sonication time to 50% and 10%. Significant improvements of drying characteristics were observed for continuous sonication and intermittent ultrasound at 50% net sonication time. Experimental data were fitted with eight models, among which the Midilli model resulted in the best fit with R2>0.9988 and reduced χ2⩽0.0002. The influence of ultrasound on drying time to reach 20% and 30% residual moisture content as well as on effective moisture diffusivities and drying periods is discussed.
ISSN:0260-8774
1873-5770
DOI:10.1016/j.jfoodeng.2011.07.018