Ethanol pre-treatment improves vegetable drying and rehydration: Kinetics, mechanisms and impact on viscoelastic properties

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Augusto P.E.D.
Rojas M.L.
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Elsevier Ltd
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Drying is a complex unit operation widely applied in food processing. There is still an increasing interest to enhance the process, as well as the product quality and properties. In this work, ethanol was used to enhance drying of pumpkin, which has been considered as a structurally representative material of plant foods. The effect of ethanol treatment on microstructure, convective drying kinetics (Page model), rehydration kinetics (Peleg model) and viscoelastic properties (generalized Maxwell model) was evaluated. The pre-treatment was conducted by immersing pumpkin cylinders in ethanol before convective drying. The ethanol treatment accelerated both drying and rehydration processes. Microstructure modifications were observed after the ethanol treatment, drying and rehydration. The rehydrated samples (control and ethanol treated) showed different viscoelastic properties compared with those in natura, which presented low stress decay and more residual elasticity. A possible mechanism was proposed. In conclusion, the ethanol improved both drying and rehydration processes, without negatively impacting on the microstructure and viscoelastic properties of pumpkin cylinders.
The authors are grateful to the São Paulo Research Foundation (FAPESP, Brazil) for funding the project nº 2016/18052-5; to the National Council for Scientific and Technological Development (CNPq, Brazil) for funding the project nº 401004/2014-7; and to Cienciactiva for the M.L. Rojas Ph.D. scholarship (CONCYTEC, Peru; Contract 087-2016-FONDECYT), from the “Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica”. The authors are also grateful to the “Laboratório de Análise de Imagens” (LPV-ESALQ/USP) for the support and facilities of X-ray analysis.
Palabras clave
Viscoelasticity, Cylinders (shapes), Ethanol, Heat convection, Kinetics, Microstructure, Thermal processing (foods), Microstructure modifications, Page models, Peleg model, Rehydration, Rehydration kinetic, Rehydration process, Viscoelastic properties, Drying