Extraction of Antioxidant Compounds from Grape Stalk Dried at Different Conditions
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.
Prof. Andreas Öchsner, Prof. Graeme E. Murch and Ali Shokuhfar
J.V. García-Pérez et al., "Extraction of Antioxidant Compounds from Grape Stalk Dried at Different Conditions", Defect and Diffusion Forum, Vols. 283-286, pp. 604-609, 2009