Abstract
Macro and micro-structural changes take place during food dehydration. Macro-structural changes encompass modifications in shape, area and volume. Studies of such changes are important because dehydration kinetics (essential for calculating industrial dryers) may be highly influenced by changes in food shape and dimensions. The overall changes in volume, surface area (“shrinkage”) and shape (Heywood factor, with provides a close description of food shape) were determined experimentally, and the results were correlated with simple expressions. Hence, although dehydration kinetics can be modeled with simplified overall shrinkage expressions, the possibility of selecting a suitable geometry and predicting the characteristics dimensions will provide higher accuracy. An additional unresolved problem is the lack of a general model that predicts macro-structural changes for various foods and diverse geometries. In this work, based on experimental data of sweet and sour cherries, and rose hip fruits, a simplified general model to predict changes in volume and surface area are proposed. To estimate how the changes in characteristic dimensions affect the kinetic studies, experimental drying curves for the three fruits by means of a diffusional model considered the following variants for the characteristic dimensions: (i) The radius of the fresh food, assumed constant; (ii) The radius of the partially dehydrated product; (iii) The radius predicted by the correlation for structural changes, especially volume, obtained in this work and generalized for the three fruits, and (iv) to demonstrate the need to study the macro-structural changes for all dehydrated foods, also be present the case of a restructured food.
Highlights
Drying is probably the oldest method used to preserve food but, nowadays, it is considered as such, and as a technique to add value to primary products
This treatment is necessary since shrinkage is neither symmetrical nor uniform in most foods, in spite of which, most researchers have assumed that shrinkage does not depend on drying operating conditions or, at most, that it depends on drying rate (Panyawong & Devahastin, 2007; Moreira, Figueiredo, & Sereno, 2000; Arnosti, Freire, & Sartori, 2000; Hatamipour & Mowla, 2002, 2003; Ratti, 1994; Raghavan & Venkatachalapathy, 1999; Schultz et al, 2007; Calli Pacco & Menegalli, 2004; Ochoa, Kesseler, Pirone, Marquez, & De Michelis, 2002a, 2002b; Ochoa, Kesseler, Pirone, Marquez, & De Michelis, 2007; Marquez, De Michelis, & Giner, 2006; Pirone et al, 2008; Marquez & De Michelis, 2011; Mabellini, Beatriz Vullioud, Alberto Marquez, & De Michelis, 2010)
The corresponding expression for surface area changes, on the other hand, was a third degree polynomial that only depends on moisture content, and it is in agreement with previous literature
Summary
Drying is probably the oldest method used to preserve food but, nowadays, it is considered as such, and as a technique to add value to primary products. Current demand for high quality products in the food market requires elevated retention of nutritional and sensory attributes in dehydrated foods compared with the fresh raw materials To this end, a complete understanding of the factors responsible for quality losses is becoming more and more important (El-Aouar et al, 2005). Some authors consider that the evaluation of particle shrinkage alone is not sufficient, since shape changes are not taken into account In this sense, several authors began to use the shape changes to some foods (Jinorose & Devahastin, n.d.; Panyawong & Devahastin, 2007; Gumeta-Chavez et al, 2011; Gaston, Abalone, Giner, & Bruce, 2003; Chaves, Sgroppo, & Avanza, 2003; Toma Vanacore, Chaves, & J.R. 2006; Costa et al, 2011; Marquez & De Michelis, 2011). The modelling of dehydration kinetics with simplified overall shrinkage models is possible, a more strict and rigorous treatment would imply the consideration of shape changes based
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