A study has been conducted on the antioxidant content and antioxidant activity in raisins from seedless hybrid varieties of vines with coloured grape juice. It has been found that the amounts of trans-resveratrol and quercetin as well as their antioxidant activity in raisins from the seedless coloured hybrid forms almost always mathematically exceed the levels of these indicators in the raisins of the Gamay Freaux, Black Corinth and Sangiovese grape varieties. It has been shown that 54% of the change in antioxidant activity is due to changes in the content of trans-resveratrol and 42% of quercetin. The applied mathematical models enable the theoretical study of the chemical composition of raisins of different grape varieties through the analytical forms of the proven relationships between them.
The process related to the changes in dimensions and mass of grape berry passes through two growth phases separated by a lag phase, and can be described by a double sigmoid curve. The onset of the growth phases and their duration are important factors for understanding the growth processes in grape berries. A new method for their quantitative determination was developed in the present study. In this method, the phase transition dates correspond to the times at which the rate of change of the curvature of the logistic (sigmoid) curve reaches an extreme value. The method was tested on three seedless grape varieties, Sultanina, Ruby Seedless and Rusalka 3, and the changes in grape berry dimensions and mass were tracked from anthesis to harvest. For each of the varieties, a double logistic model of change in berry length, width and mass from anthesis to harvest was developed and the metrics of growth - beginning, stabilisation and end of growth - for each of the two phases were determined. It was found that the metrics in mass and berry dimensions do not match and shift relative to each other over time. A comparison of growth metrics with phenological metrics, such as anthesis, veraison and ripening, showed that phenophases cannot be used as a time scale to record the acceleration of growth processes, as they shifted in time with growth metrics. An exception was veraison, which coincided with the beginning of the accelerated growth of grapes during the second growth phase, following the lag phase. The time scale presented in the current research is a new tool for monitoring growth processes and could help clarify the links between visible changes in the grape berries and the ongoing processes within them. The developed method can also be used for the analysis of various growth processes that follow the logistic law.
The study presents the analysis of the influence of summer pruning operations (defoliation, cluster thinning) on the parameters of a potential productivity of winter buds at the vine variety Vranec grown near Veles in the period 2013-2015. For this research, four treatments were set: control, defoliation and two types of cluster thinning: 10 and 6 clusters per vine. From the obtained results it is found that there are no injuries in the main winter buds during the vegetation period and the potential fruitfulness is determined by higher coefficient, 1.38, which depends on the location along the cane. The yield at this variety will be formed mainly by clusters with size of 350-550 μm, followed by those with the length of 550-750 μm. The application of defoliation and regulation of the vine yield has a beneficial effect on increasing the rate of potential fruitfulness of winter buds, the number of buds with 2 and 3 clusters, increasing the inflorescences with a length of 350-550 μm and the appearance of those longer than 750 μm.
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