Marko Karoglan

Differences in the levels of pesticides, metals, sulphites and ochratoxin A between organically and conventionally produced wines

Organic products are generally recognized to be healthier and safer than conventional products. However, the actual scientific data regarding the importance of organic production on particular contaminant/additive content of wines is scarce. This study aimed to evaluate contents of pesticides, metals, sulphites and ochratoxin A in organically (org) and conventionally (conv) produced wines from eleven locations in different winegrowing regions of Croatia. All wines contained significantly lower levels of residues as compared to the maximum limits (MLs) with the exception of excessive amounts of Cu and Zn in one sample. Pb and Mg were mainly significantly less represented in org wines. There were no significant differences in the content of sulphite or ochratoxin A between org and conv wines. Significantly lower total pesticide concentrations and average number of pesticides per sample were obtained in org wines. The majority of ochratoxin A positive wines were from conv wine producers.

Effect of cluster thinning on fruit composition of Vitis vinifera cv. Pinot noir (Vitis vinifera L.)

The technique of cluster thinning is being used in aim to reduce the crop load of vine in order to improve the quality of grapes. The aim of the trial was determination the optimal timimg for thinning regarding the results given from chemical analysis of the must immediately after the harvest. The experiment was conducted at the experimental station of the Faculty of Agriculture in Zagreb in 2006 and 2007 years, on cv. Pinot noir according to the random block design system. The cluster thinning was performed with 40 % intensity in three terms; immediately after the flowering period (P1), three weeks after the flowering period (P2) and with the begining of veraison (P3). The results were compared with the results of the control treatement without cluster thinning performance. The analysis of variance of given data has shown a significant difference in must composition between the terms of cluster thinning and a control treatement, and yield per vine has not been reduced with earlyer term of cluster thinning.

The effect of grape harvest date on polyphenols and anthocyanins content of different red grapes varieties

Four red grape cultivars were investigated in order to study the effect of grape harvesting date (ripening stage of the grape) on traditional indicators of maturity such as soluble solids and titratable acidity content, as well as on their total polyphenols and total anthocyanins content. Grape varieties grown in different coastal vinegrowing regions, at three different harvesting dates, and from two consecutive vintages, were examined. The results showed uncertainty of traditional indicators of maturity as the only parameter for harvest date determination, since the maximum concentration of soluble solids didn’t correlated with maximum concentration of total polyphenols and anthocyanins in the most of harvest dates. Furthermore, grapes from the third harvest date mostly didn’t have consistently higher polyphenols and anthocyanins levels, so the harvest should not be postponed unduly.

Total and yeast assimilable nitrogen composition in grape juices of three grapevine cultivars as affected by vineyard nitrogen fertilization

Nitrogen fertilization is one of the common agrotechnical practices in vitculture, by which we can achieve higher content of nitrogen compounds in grapes. The purpose of this research was to determinate the influence of nitrogen fertilization on total nitrogen, free amino nitrogen and ammonia composition in grapes of Chardonnay, Italian Riesling and White Riesling cultivars. Research was laid out in the 2006 and 2007. Experiment was random block design with 3 repetitions, and fertilization was in the form of urea, as follows: 0 kg/ha - K, 51 kg/ha (23 kg N/ha) –N1, 152 kg/ha (70 kg N/ha) – N2 te 254 kg/ha (117 kg N/ha) –N3. The grapes were harvested according to repetitions. The obtained research results indicated a positive effect of nitrogen fertilization on all of examined nitrogen compounds.

Effect of grapevine solarization on the anthocyanin composition of Pinot Noir wines

Maize (Zea mays L.) genotypes wit It improved nitrogen utilization efficiency (NUE) are of interest to growers. Field experiments were conducted to evaluate the total N uptake in the aboveground biomass and NUE (kg grain per kg of N absorbed in the aboveground biomass). Four commercial hybrids of similar maturity ranking were grown under the high-N (200 kg N ha(-1)) and low-N (1100 kg N ha(-1)) fertilization rates over three years. Growing conditions significantly affected hybrid performance for NUE, which ranged from 42 kg grain kg N-1 in the low-yielding (dry) environment to 55 kg grain kg N-1 under higher yielding environment, When compared to the low-N rate, the average N uptake was by 32% higher at the high-N rate, whereas smaller differences occurred for the aboveground biomass (12%), grain yields (14%), stover N (28%) and grain N (13%) concentrations. Significant differences existed among tested hybrids for grain yield, aboveground biomass, grain and stover N concentration, N uptake and consequently NUE.Hairy vetch (Vicia villosa Roth) and crimson clover (Trifolium incarnatum L.) were evaluated as cover crops during two vegetation seasons in the Mediterranean and Continental area of Croatia. Better tolerance to low winter temperatures was observed for crimson clover. Higher plants (10 to 3 1 cm) before winter and in spring (67 to 117 cm) were measured for hairy vetch, while crimson clover had higher yields of fresh biomass (33.7 to 113.1 t ha(-1)). Concentrations of N (1.53 to 3.34%), P2O5 (0.55 to 1.04%) and K2O (2.02 to 5.32%) in plant tissue were higher for hairy vetch. However, due to higher yields of dry matter, crimson clover accumulated more N (105 to 239 kg ha(-1)), P2O5 (28 to 83 kg ha(-1)), and K2O (105 to 440 kg ha(-1)) than hairy vetch. According to our results crimson clover could be recommended as a cover crop in Mediterranean and Continental area of Croatia.