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Grape drying is a slow and energy intensive process because the waxy peel has low permeability to moisture.\ud Therefore, peel chemical and physical pretreatments are considered before drying in order to facilitate\ud water diffusion. However, they cause heterogeneity in the waxes removal and problems during\ud shelf-life.\ud In this paper an alternative abrasive pretreatment of grape peel, for enhancing the drying rate and preserving\ud the samples, was applied to Red Globe grapes. Convective drying experiments were carried out at\ud 40–70 !C and at 2.3 ms!1 air velocity. The effect of wax abrasive pretreatment on the drying kinetics and\ud quality parameters of raisins was investigated. The results were compared with those of samples pretreated\ud by dipping in alkaline ethyl oleate solution and untreated grapes. All the dried samples are darker\ud than fresh one and shrunked. The samples pretreated by peel abrasion and dried at 50 !C showed the lowest\ud color changes, less shrinkage and the best rehydration capacity. The drying kinetics and shrinkage\ud curves were also analyzed using some commonly available empirical models

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Fundamental understanding on microscopic physical changes of plant materials is vital to optimize product quality and processing techniques, particularly in food engineering. Although grid-based numerical modelling can assist in this regard, it becomes quite challenging to overcome the inherited complexities of these biological materials especially when such materials undergo critical processing conditions such as drying, where the cellular structure undergoes extreme deformations. In this context, a meshfree particle based model was developed which is fundamentally capable of handling extreme deformations of plant tissues during drying. The model is built by coupling a particle based meshfree technique: Smoothed Particle Hydrodynamics (SPH) and a Discrete Element Method (DEM). Plant cells were initiated as hexagons and aggregated to form a tissue which also accounts for the characteristics of the middle lamella. In each cell, SPH was used to model cell protoplasm and DEM was used to model the cell wall. Drying was incorporated by varying the moisture content, the turgor pressure, and cell wall contraction effects. Compared to the state of the art grid-based microscale plant tissue drying models, the proposed model can be used to simulate tissues under excessive moisture content reductions incorporating cell wall wrinkling. Also, compared to the state of the art SPH-DEM tissue models, the proposed model better replicates real tissues and the cell-cell interactions used ensure efficient computations. Model predictions showed good agreement both qualitatively and quantitatively with experimental findings on dried plant tissues. The proposed modelling approach is fundamentally flexible to study different cellular structures for their microscale morphological changes at dehydration.

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