Papers by Author: G. Clemente

Abstract: Grape pomace is the main by-product from the wine industry. It is principally made up of grape skin and seeds. Drying this by-product is the first step for the later extraction of components with high added value like oil or antioxidants. Due to the different characteristics of the components, the study of the drying kinetics of grape pomace must be addressed taking its components into account one by one. For that purpose, grape seeds from the Spanish wine industry were dehydrated in a convective laboratory dryer at 70 °C and at 1, 2 and 3 m/s until a weight loss of 40% was reached. Drying kinetics was determined in triplicate. Modelling was carried out by means of a diffusion model without considering shrinkage and external resistance. Grape seeds were assumed to be spherical. For all the fits, the explained variance was higher than 96.9 % and the mean relative modulus was lower than 1.7 %. Between 1 and 2 m/s, effective diffusivity increased in line with air velocity, although the values of effective diffusivity calculated for 2 and 3 m/s were similar. It seems to indicate that for the experimental conditions under study, the external resistance is not negligible at 1 and 2 m/s and for higher air velocities the internal resistance to mass transfer controls the drying process. These results coincide with those found by other authors when studying different food products.

Abstract: Intermittent drying is an alternative technology to continuous drying that improves the product quality as result of diminishing the average material temperature and the heating time. In this study, the application of the intermittent drying technology to mango drying (Mangifera indica L.) was analyzed and optimized. To formulate the optimization problem, an objective function was proposed in order to improve the product quality and decrease the energy consumption. To quantify the objective function, a mathematical model for a cubic shape was formulated and validated, considering diffusional mass and heat transfer with non-negligible external resistances.

Abstract: Grape stalk may be considered as an agro-food byproduct of the wine industry, being considered as a potential source of antioxidant compounds. Actually, before the extraction of antioxidants a previous stage of drying would be necessary. Stalks obtained from a red wine processing (Vitis vinifera var. Bobal) were characterized as a cylinder net with different size ending in spheres. The average diameters and mass fractions of the individual parts of the stalk were measured: spheres (4.4±0.7 mm and 0.352 mass fraction), large cylinders (3.3±0.6 mm and 0.204 mass fraction), intermediate cylinders (2.1±0.4 mm and 0.294 mass fraction) and small cylinders (1.1±0.3 mm and 0.150 mass fraction). Drying kinetics of each one of the parts of the stalk were carried out at 40 °C and 2 m/s using an initial mass load of 30 g. Furthermore, drying experiments of the whole stalk were conducted at the same experimental conditions. Different diffusion models were considered to predict the drying kinetics for each one of the individual parts of the stalk according to the geometry considered. A diffusion model for the whole stalk was developed by adding the individual diffusion models weighed by the corresponding mass fractions. The diffusion models considered fitted properly the drying kinetics of the individual parts considered on the stalk. The figures of the effective moisture diffusivity identified for the different kinds of cylinders were close (1.07-1.78 10-11 m2/s), however, the spheres showed a different behavior characterized by a significantly higher figure of effective moisture diffusivity (3.92 10-8 m2/s). Finally, the usefulness of the model considered to describe the drying kinetics of the whole stalks was shown.