Papers by Author: M. Blasco

Abstract: The olive crop has a great importance in the economy of Spain. Every year during the pruning of the olive trees a significant quantity of leaves are cut and discarded. It is known that these leaves constitute a source of antioxidant compounds and its processing would provide an added value to this raw material. Antioxidant compounds may be damaged when drying, the previous process to extraction. Thus, the goal of this work was to study the influence of the high intensity ultrasound applied during the drying of olive leaves on the kinetic of extraction of antioxidants compounds. From the parameters identified from Naik model, it can be concluded that the application of high intensity ultrasound during drying reduced the antioxidant activity of extracts at the equilibrium but increased the initial extraction kinetic compared to conventional hot air drying. This last aspect could have high interest to the antioxidant extraction from an industrial scale point of view.

Abstract: Grape stalk constitutes a by-product of wineries with low economic value. The extraction of compounds with antioxidant capacity may be considered as an alternative to increasing its value. Prior to extraction there must be a drying process, which may affect not only the product structure but also the antioxidant activity of extracts. The aim of this work was to address the influence of grape stalk drying conditions on the subsequent extraction of antioxidant compounds. Prior to the extraction experiments, grape stalk was dried under different conditions: freeze dried and hot air dried at different temperatures (40, 70 and 100 °C). The extraction experiments were carried out at 60 °C using ethanol-water (80 % v/v) as solvent. Extracts were taken after 5, 10, 15, 30, 60, 120, 180, 240 and 1380 min. Antioxidant concentration in the solvent was evaluated by measuring the total antioxidant activity using the FRAP method. Extraction kinetic was modelled from the evolution of antioxidant concentration in the solvent using a diffusion model. Extracts obtained from freeze dried samples presented the highest antioxidant concentration, almost double that from hot air dried samples. Among these, the highest antioxidant concentration was found for samples dried at 100 and 40 °C. The freeze dried samples also showed the highest kinetic parameters: effective antioxidant diffusivity and mass transfer coefficient.

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.