Neus Bellí

Incubation time and water activity effects on ochratoxin A production by Aspergillus section Nigri strains isolated from grapes.

Aims:  The objective of this study was to determine the temporal ochratoxin A (OTA) accumulation profile of Aspergillus section Nigri at different water activity (aw) levels.

Aspergillus carbonarius growth and ochratoxin A production on a synthetic grape medium in relation to environmental factors.

Aims:  The effects of water activity (0·90–0·99 aw), temperature (15–37°C), and their interaction on growth and ochratoxin A (OTA) production by eight isolates of Aspergillus carbonarius were investigated on synthetic nutrient medium (SNM) with composition similar to grapes.

Review: Ochratoxin A (OTA) in Wines, Musts and Grape Juices: Occurrence, Regulations and Methods of Analysis:

This work gives a general overview of ochratoxin A (OTA) occurrence in wines and the methodology for OTA analysis. The results of more than two thousand samples taken from the literature have been taken into account to quite extensively describe the present situation of OTA contamination of wine. According to these data, OTA is much more commonly detected in red wines than in rosé and white wines, and OTA concentration is remarkably higher than in the latter ones. Thus OTA could be detected in 45% (median 34%) of white wine samples, whereas it was detected in 66% (median 66%) of rosé and 71% (median 90%) of red wine samples. When comparing the wines from Northern and Southern regions, the latter showed a higher contamination than those from the Northern area. It has been suggested that OTA accumulation could be due to fungi belonging to the genus Aspergillus in wines from Southern European countries because the crops are exposed to elevated temperatures, which favour growth of OTA-producing Aspergillus species over Penicillium. High performance liquid chromatography (HPLC) associated with fluorescence detection preceded by extraction of OTA using commercially available immunoaffinity columns (IAC) is currently the most applied method for OTA determination in wines.

Two-dimensional profiles of fumonisin B1 production by Fusarium moniliforme and Fusarium proliferatum in relation to environmental factors and potential for modelling toxin formation in maize grain.

This study has examined in detail the effect of temperature (7-37 degrees C) and water availability (water activity, a(w), 0.89-0.97) on fumonisin B1 (FB1) production by an isolate of Fusarium moniliforme and F. proliferatum on irradiated maize grain after incubation for 28 days. The optimum conditions for F. moniliforme and F. proliferatum were 30 degrees C at 0.97 a(w) and 15 degrees C at 0.97 a(w), respectively. The maximum concentrations were 2861 mg kg(-1) and 17,628 mg kg(-1) dry wt. maize grain, respectively. At marginal a(w)/temperature conditions for growth (e.g. 0.89-0.91 a(w)) no FB1 was detected (<0.1 mg kg(-1)). A high variability was found between replicates for F. moniliforme, but not for F. proliferatum. These data were used to construct two-dimensional diagrams of all the a(w) x temperature conditions favourable for FB1 production for the first time. The data were also subjected to a polynomical regression, which demonstrated that there was a very good fit for the 15-30 degrees C range of temperature and at 0.97 a(w). However, at marginal environmental conditions this was not possible. This suggests that it may be possible to predict within a limited environmental range the potential for significant FB1 production.

Impact of fungicides on Aspergillus carbonarius growth and ochratoxin A production on synthetic grape-like medium and on grapes

A study was undertaken to evaluate the impact of the application of several fungicide treatments used in Spanish vines on Aspergillus carbonarius growth and ochratoxin A production. Three trials were designed in order: (1) to screen 26 fungicides at the doses recommended by manufacturers on grape-like synthetic medium at 20 and 30°C; (2) to find out the minimum inhibitory concentration of each fungicide for A. carbonarius growth on synthetic medium; and (3) to investigate the effect of several fungicides on A. carbonarius-inoculated grapes. In synthetic medium nine fungicides significantly reduced A. carbonarius growth rate. Meanwhile, 13 fungicides completely inhibited its growth. In general, growth was faster at 30°C than at 20°C, contrary to ochratoxin A production. Fungicides that stopped fungal growth also inhibited ochratoxin A production, but not all the fungicides that reduced growth reduced the ochratoxin A synthesis. In general, fungicides that contained copper or strobilurins reduced both growth and ochratoxin A production, contrary to sulphur fungicides. At the optimum temperature for A. carbonarius growth of 30°C, higher amounts of fungicide were needed to prevent fungal growth than at 20°C. Among the fungicides that inhibited A. carbonarius growth on synthetic medium at the initial doses, cyprodinil seemed to be the active ingredient more effective at stopping fungal growth when testing reduced doses. The fungicide effect on grapes was similar to that on synthetic medium. Both infection and ochratoxin A production were reduced when using cyprodinil (37.5%) plus fludioxonil (25%) and azoxystrobin (25%). Penconazole (10%) also showed a clear reduction in ochratoxin A production at both temperatures, although infection was only reduced at 20°C. Ochratoxin A reduction was strain and temperature-dependent. In general, fenhexamid (50%), mancozeb (80%) and copper hydroxide (80%) plus copper (50%) enhanced infection and ochratoxin A production.

Effect of chemical treatments on ochratoxigenic fungi and common mycobiota of grapes (Vitis vinifera).

The effect of the application of two fungicides (cyprodinil alone and a mixture of cyprodinil and fludioxonil) on the mycoflora of grapes, especially ochratoxigenic fungi, was studied. Different doses and application times were analyzed. Grape mycobiota was isolated and identified, and the classification of black aspergilli was carried out. We found that 81.7% of the isolates belonged to Aspergillus niger aggregate and 18.3% to Aspergillus carbonarius. The ability to produce ochratoxin A (OTA) was studied on Czapek yeast extract agar (CYA) medium in 238 isolates. Most A. carbonarius (97.2%) produced detectable amounts of OTA, while only 2.9% of the A. niger aggregate were OTA producers. Most of the isolates (58%) produced less than 2.5 microg OTA per g of CYA. That, together with the highest levels of black aspergilli detected near harvest, proved the reported theory that they are primarily responsible for OTA in grapes. The fungicides studied had a significant effect on black aspergilli in three of the four vineyards sampled, as the natural increase of black aspergilli when approaching harvest was in general lower in all the fields treated with fungicides as compared to the control treatment. A mixture of cyprodinil (37.5%) and fludioxonil (25%) applied at veraison and 21 days before harvest was the most effective treatment to prevent black aspergilli in grapes, together with a single application of this mixture at veraison followed by an application of cyprodinil (50%) 21 days before harvest. No OTA was detected in musts (n=112) produced from either the control treatment or the treated grapes.