Effect of structural characteristics as changes in volume, surface

ANTONIO DE MICHELIS; CARLOS ALBERTO MÁRQUEZ; ALEJANDRA MABELLINI;ELIZABETH OHACO; SERGIO ADRIÁN GINER.

Advanced Food Process Design: A structural approach

Springer Science+Business Media, LLC.

Año: 2011;

Macro and micro structural changes take place during food dehydration. Macro structural changes encompass modifications in area and volume, often referred as "shrinkage". Studies of such changes occurring in biological tissues are complex if analyzed from the chemical and physical viewpoint; however, their elucidation is important because dehydration kinetics may be highly influenced by changes in food geometrical dimensions. Most previous research have proposed the experimental route under controlled operating conditions of drying, correlating the results with simple expressions to take into account the overall changes in volume and surface area of the product. However, determination of volume and area changes is not enough as they do not consider shape modifications. Therefore, experimental measurements to determine the so called Heywood shape factor were carried out. This factor is defined as the ratio of the actual volume to the equivalent diameter of the particle, and provides a close description of food shape. This procedure is necessary due to nonsymmetrical shrinkage, and implies a contribution because, unlike shrinkage which is reported to be independent of drying conditions or at most dependent on air velocity or drying method, there is evidence on that the shape does change with method or velocity. Therefore, although dehydration kinetics can be modeled with simplified overall shrinkage expressions, the possibility of predicting the characteristics dimensions will provide higher accuracy. Besides, the ability of predict shape will allow to deal with important issues as the quality of the final product, and will possibly allow us to find dehydrations conditions 5 heading to minimum quality losses. 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 changes in volume, surface area and shape, measured in cherries, sour cherries and rose hip fruits, a simplified general model to predict changes in volume and surface area are proposed, which are compared with values published for other fruits. Otherwise, the Heywood shape factor were evaluated for the fruits considered in this work, in order to select a suitable geometry with which to predict the characteristic dimensions for using in modeling. Besides, in order to asses the manner in which the changes in characteristic dimensions (caused by structural changes) affect the kinetic studies, experimental drying curves for the three fruits by means of a diffusional model considering the following variants for the characteristic dimension: (i) That of the fresh food, assumed constant (this assumption was employed by many authors of published papers); (ii) That of the partially dehydrated product; (iii) That predicted by the correlation for structural changes, specially volume, obtained in this work and generalized for various fruits.