Fungal diversity in the grapes-to-wines chain with emphasis on Penicillium species

The aim of this work was the description of surface and endogenous mycobiota colonisation of grapes, fresh grape juice, grape must, and wine primarily focused to the current spectrum of the penicillium species. One sample of white grape variety Palava and one sample of blue grape variety Dornfelder were collected in Small Carpathian wine growing region of Slovakia in the year 2017. Direct plating of grapes on agar plates was used for analysis of surface mycobiota of grapes while surface sterilsed grapes were used for endogenous mycobiota analysis. Mycobiota of juice, must, and wine was analysed by plate dilution method. Overall, we isolated 148 strains belonging to 13 genera of filamentous microscopic fungi and Mycelia sterilia from grape variety Palava, while the most frequent was Alternaria. Alternaria was the most common genus in the surface and endogenous colonisation with an average relative density 50% and 73.6%, respectively. A total of 2 species of Penicillium were detected from the grapes to wine, potentially toxigenic Penicillium expansum and P. chrysogenum. A total of 39 strains belonging to 6 genera and Mycelia sterilia were identified from grape variety Dornfelder. The most abundant genus was also Alternaria (51.3%), followed by Penicillium (12.8%). Alternaria was the most common genus in the surface and endogenous colonisation  and fresh grape juice with an average relative density from 20% (grape juice) to 71% (endogenous colonisation of grapes). A total of 3 species of Penicillium were detected from the grapes to wine, where Penicillium expansum were detected most commonly. In the second part of our work some selected isolates were tested to the ability to produce mycotoxins such as patulin, citrinin, and roquefortin C in in vitro condition by thin layer chromatography method. All tested  strains of Penicillium species were able to produce at least one mycotoxin. 

Influence of harvest day on changes in mechanical properties of grape berries

Changes in the composition, physical and mechanical properties occur in grape berries during the ripening process, but the heterogeneity of the grapes harvested at different ripening stages affects the reliability of the results obtained. The characterization of the mechanical properties of grape berries seems to be an important parameter for understanding grape ripening. In this work, these changes were studied in seven grapevine varieties (Riesling, Blaufränkisch, Pinot Noir, Cerason, Malverina, Laurot, and Hibernal) harvested during six consecutive weeks. Mechanical behaviour was measured using compression and puncture tests using of TIRATEST 27025 testing machine. Skin mechanical properties were evaluated using a puncture test carried out on the equatorial side. The dependence of these properties on the chemical composition has been evaluated. These parameters of force/time curves were studied by puncture test: the berry skin break force, the needle displacement at the skin break and the berry skin break energy. The crushing force, the plate displacement at the crushing strength and the berry crushing energy were studied from force/time curves by compression test. Results of the puncture test shows that there the skin break strength and the acidity content are monotonic functions of the time. A comparison of different varieties from the point of the value of the crushing force was obtained by vertical and transversal loading. The crushing force is monotonically decreasing function of the harvesting time like the break force evaluated at the puncture test. The correlation between the skin break strength and the sugar content is significant namely for the varieties: Hibernal, Riesling, Malverina, and Cerason.