This thesis dealing with the study of antioxidant capacity was developed between 2006-2011 at the Department of Post-Harvest Technology of Horticultural Products, Faculty of Horticulture, Mendel University in Brno. The aim of this thesis was the evaluation of photo-chemiluminescence method and its optimization for determining the antioxidant capacity by the Bux Photochem device. The assessment of impact of selected substances and treatment of experimental material on measured values of antioxidant capacity. The other aim of this thesis was the monitoring of development of antioxidant capacity of the grapes during ripening period and during the process of alcoholic fermentation. The basic principles of measuring the antioxidant capacity by photo-chemiluminescence method are provided by compliance of the methodology with an emphasis on the same treatment of the device. The work showed that the dilution of the observed samples affects the antioxidant capacity measured by Photochem Bux PCL. The solutions of the reference wine and the antioxidant rutin showed higher antioxidant capacity at the samples with higher dilution level. At the parallel extraction by non-polar and polar extractants and the subsequent summation of the measured values of TAC was shown that the resulting value was higher than at the consecutive extractions. Therefore the summation of the values is not appropriate for parallel extractions of antioxidants obtained from the extractants with various polarities. During the extractions 75% methanol was evaluated as the best extractant of antioxidants present in grapes. It is necessary to homogenize the sample before extraction. All the extraction operations must be finished in the shortest time possible. It was shown that all the extraction operations apart from used extractant and re-extraction have demonstrable effects on degradation of antioxidants extracted from the samples. Therefore it is necessary to describe all the extraction procedures perfectly. Very suitable extraction procedure is a re-extraction. There is a big difference in concentrations of extracted substances and extractant occurring during re-extraction, so the extraction is very effective. It was observed that one of the factors causing the degradation of antioxidant compounds during the extraction procedures is the presence of atmospheric oxygen. Sulphites present in wine do not affect the value of antioxidant capacity measured by photo-chemiluminescence method. Conversely, FRAP method has a positive response to the presence of sulphites in wine, so the values measured by this method are affected by the sulphites content. The impact of alcohol content on antioxidant capacity measured by photo-chemiluminescence method was not demonstrated. The monitoring of the antioxidant capacity development in grapes during the ripening period showed that the white varieties have no characteristic development. The blue varieties showed that during the ripening period the values of antioxidant capacity were gradually increasing up to three times the first measurement (46 days before the harvest). The antioxidant capacity of grape juice was increasing during the alcoholic fermentation only if the juice was left in the contact with skins. There was no increase of antioxidant capacity observed after the pressing, although the fermentation process was highly reductive and took place in closed containers.
| Identifer | oai:union.ndltd.org:nusl.cz/oai:invenio.nusl.cz:249329 |
| Date | January 2012 |
| Creators | Híc, Pavel |
| Source Sets | Czech ETDs |
| Language | Slovak |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis |
| Rights | info:eu-repo/semantics/restrictedAccess |
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