Water loss of fruit during storage has a large impact on fruit quality and shelf life and is essential to fruit drying. Dehydration of fruit tissues is often accompanied by large deformations. One-dimensional water transport and large deformation of cylindrical samples of apple tissue during dehydration were modeled by coupled mass transfer and mechanics and validated by calibrated X-ray CT measurements. Uni-axial compression-relaxation tests were carried out to determine the nonlinear viscoelastic properties of apple tissue. The Mooney-Rivlin and Yeoh hyperelastic potentials with three parameters were effective to reproduce the nonlinear behavior during the loading region. Maxwell model was successful to quantify the viscoelastic behavior of the tissue during stress relaxation. The nonlinear models were superior to linear elastic and viscoelastic models to predict deformation and water loss. The sensitivity of different model parameters using the nonlinear viscoelastic model using Yeoh hyperelastic potentials was studied. The model predictions proved to be more sensitive to water transport parameters than to the mechanical parameters. The large effect of relative humidity and temperature on the deformation of apple tissue was confirmed by this study. The validated model can be employed to better understand postharvest storage and drying processes of apple fruit and thus improve product quality in the cold chain.
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Acknowledgements The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 245288. The authors would also like to acknowledge the Fund for Scientific Research—Flanders (grant no. FWO G.0603.08), the K.U. Leuven (project OT 08/023), and the EC (FP7-226783 project InsideFood) for financial support. Thijs Defraeye is a postdoctoral fellow of the Research Foundation—Flanders (FWO).
- Cellular tissue
- Nonlinear viscoelastic models
- Water transport