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Noble rot of the grape is a complex microbiological-biochemical process having grate importance in the Tokaj wine district. In this study, morphology and development of Botrytis cinerea in the berry skin as well as the presence of other moulds and yeasts on the digested exocarp of the noble rotted grapes (aszú) were investigated and presented by scanning electron microscopy. Another aim of this work was a comprehensive taxonomical characterisation of the yeasts present on the surface of the “aszú” berries in the Tokaj wine district in five vintage years. The dominant yeasts were isolated and taxonomically identified according to phenotypical properties. The most prevalent yeast species of the aszú grapes were Metschnikowia pulcherrima in the vineyard and Candida stellata in the winery (the latter species has been recently differentiated for two species, C. stellata and C. zemplinina). These two Candida species seem to be typical yeasts of Tokaj aszú berries, particularly after picking, transporting and storage of the aszú grape. These postharvest operations significantly influence mould and yeast populations of botrytized grapes.

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The most important base material of the famous wine Tokaji Aszú is the noble rotted grapes attacked by Botrytis cinerea under special conditions. The objective of this study was to determine the quantitative and qualitative composition of the yeast and mould biota present on the surface of aszú-berries in the year of 2000 and 2001, and to compare these findings with the observations made in previous vintages. The studied years represented extremely different conditions for the noble rot, so the effect of the vintage on the quantitative and qualitative composition of the microflora was more pronounced than in the earlier years. The excellent year of 2000 resulted in yeast and mould counts (mean logarithmic values are of 4.47 and 4.72) significantly lower than found in the extremely poor vintage of 2001 (meanain values areof  6.58 for yeasts and 7.10 for total moulds). The place of sampling (vineyard or winery) had less impact on the quantitative composition of the microbiota, than found in in the formerprevious, less extreme years. The results of qualitative analysis, however, confirmed that the taxonomic composition of the yeast biota depends on the place of sampling, showing that the storage conditions of aszú grapes before vinification should be studied and optimized.

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Initiated by the Association “Wine Route of Etyek Wine District”, the objectives of this study were to isolate and identify autochthonous yeast strains from local wines and to determine their oenologically important properties. The first aim of this work was to characterize the taxonomic and phenotypic diversity of the representative Saccharomyces yeast strains that dominate the spontaneous fermentations in this wine district. The results obtained by molecular ribotyping (ARDRA) revealed a strong dominance of S. cerevisiae, but S. bayanus var. uvarum was also present sporadically. Some of the natural isolates exhibited high volatile acid production or poor fermentation capacity, which imply a quality risk in spontaneous fermentations. Most of the isolates, however, displayed good oenological features during lab scale fermentations. As the second aim of this work, the most promising, selected strains were further tested for oenological properties in microvinification scale and, finally, in large scale fermentations. The analytical and sensory analysis proved that selected strains, including S. bayanus var. uvarum, can be used as local starter cultures, which may contribute to the typicality of the local wines in comparison with commercial starters.

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During the analysis of environmental risk posed by hazardous waste disposal sites, ecological impact on whole ecosystems should be assessed. It requires a complex testing scheme where surrogate species represent key elements of the ecosystem. However, different organisms are exposed to a differing degree, also, their sensitivity to the same contaminant may vary. A possible way to determine which test reflects most the actual toxic conditions, correlation can be calculated between the measured ecological parameter (such as growth inhibition, mortality, etc.) and  a contaminant gradient. The basic aim of this study was to determine which ecotoxicological test shows the best correlation with the measured analytical parameters. The selected tests were Lemna minor (representing primary producers), Thamnocephalus platyurus (a primary consumer organism) and Vibrio fischeri (decomposer). When testing soil samples, the Thamnocephalus test showed excellent consistency with most contaminants but was oversensitive in the case of groundwater samples. The Vibrio fischeri bioluminescence inhibition test (ToxAlert) behaved in a different way, reflecting well the distribution of most contaminants in groundwater samples. Finally, Lemna test proved to be completely inadequate.

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Medium chain fatty acids are candidates of partial sulphur dioxide replacement in wine, as a solution to the growing consumer concerns about chemical additives. In botrytised sweet wine specialties, large amount of sulphur dioxide addition is one of the effective practices to stop alcoholic fermentation. Increasing medium chain fatty acid levels up to 80 mg l-1 was tested as a sole inhibitor on solid agar surface. S. bacillaris seemed to be the most sensitive, S. cerevsisiae and S. bayanus were more tolerant, while Z. bailii showed the highest tolerance. Then, increasing medium chain fatty acid levels up to 40 mg l-1 combined with 100 mg l-1 sulphur dioxide was introduced into a Tokaj Essence under refermentation. After 56 days, the highest dosage had pronounced effect on the yeast population, but the refermentation was not inhibited completely. Medium chain fatty acids have varying inhibitory effect on botrytised wine-related yeasts, moreover, it could be used effectively in media with high ethanol content, unlike Tokaj Essence.

Open access
Acta Alimentaria
Authors:
M. Tóth-Markus
,
I. Magyar
,
K. Kardos
,
L. Bánszky
, and
A. Maráz

In this study the role of different yeast strains in the production of volatile flavour components of Tokaji Aszú wine was tested. The effect of a Saccharomyces cerevisiae starter and that of the typical endogenous Candida stellata strain as well as spontaneous fermentation were studied and compared. For the fast comparison of aroma profile, a solid phase microextraction (SPME) sampling and a GC-MS separation and identification were used. Thirty of the present compounds were selected to characterise the changes of flavour. Significant differences were found between wines fermented with different yeast strains. Application of a Saccharomyces cerevisiae starter alone accelerated the fermentation but this caused only little change in the aroma profile and content. Candida stellata contributed weakly to the production of aroma, especially to that of the longer carbon chain ethyl esters. Characteristic compounds of aged wine were detected in bottle aged Tokaji Aszú. The change of aroma profile as a function of bottle storage time was studied. The concentrations of vitispirane, trimethyl dihydronaphtalene, 2-phenylethanol and diethyl succinate increased in the course of ageing time, while those of 3-methyl-butyl acetate, ethyl hexanoate, ethyl octanoate, ethyl decanoate and ethyl dodecanoate decreased.

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In this work, the application of an electronic tongue (ET) based on a specific ion-selective sensor array for discrimination of different white wine types is presented. The electronic tongue equipped with specific sensor array containing seven IFSET sensors was used to analyze wine samples. The obtained ET responses were evaluated using different pattern recognition methods. Principal component analysis (PCA) provides the possibility to identify some initial patterns. Linear discriminant analysis (LDA) was used to build models to separate white wine samples based on wine regions and grape cultivars. The results showed that every group was distinguished from each other with no misclassification error. Furthermore, the sequence of the wine sample groups was similar to the increasing total acidity content. Partial least square (PLS) regression was used to build models for the prediction of the main chemical compositions of the wine samples based on the electronic tongue results. The closest correlation (R2=0.93) was found in case of ‘total acidity’, and the prediction error (RMSEP) was 6.9%. The pH of the wine samples was predicted with good correlation (R2=0.89) but higher prediction error (RMSEP=10.71%) from the electronic tongue results. The ET combining these statistical methods can be applied to determine the origin and variety of the wine samples in easy and quick way.

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Acta Alimentaria
Authors:
R. Juhász
,
P. Merész
,
I. Dalmadi
,
N. Adányi
,
A. Halász
,
A. Lugasi
,
I. Magyar
, and
R. Tömösközi-Farkas
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