11 Wine Spoilage by Fungal Metabolites 623
by high aw(0.98) and temperature (28◦C), whereas OTA production was increased
at mild temperature (20◦C) and 0.96–0.98 aw. In addition, Astoreca et al. (2007)
found that optimum conditions of awand temperature are more restrictive for OTA
production than forAspergillusgrowth. The influence of relative humidity, rain or
high awis less important than the influence of high temperature (Bell ́ı et al. 2007;
Medina 2007), explaining the occurrence of these fungi in hot and dry climate
regions (Hocking et al. 2007). The influence of awappears to be more important
in dried grapes, where black sultanas (aw= 0.629) showed levels of OTA higher than
10
g/kg when white sultanas (aw= 0.567) did not (Iamanaka et al. 2006).
The frequency of the occurrence of OTA producing species on grapes is then
essentially limited to conditions of high humidity and temperature, typical of sub-
tropical and Mediterranean climates. In fact, OTA has been detected on grapes
produced in France, South America, Spain,Italy, Portugal, Greece and Australia
(as revised by Leong et al. 2006a), that have some wine regions with climatic
conditions favouring black aspergilli species. In general,A. carbonariusis highly
dominant, particularly in warmer regions, because their black spores are resistant
to UV light and sun-drying (Leong et al. 2006a). However, in colder regions such
as Germany, Northern Hungary, the CzechRepublic or Northern parts of Portugal,
France and Italy, black aspergilli have not been isolated from grape berries in spite
of the presence of OTA in wines (for references see Blesa et al. 2006 and Varga
and Kozakiewicz 2006) suggesting that other species, mainlyPenicillium, adapted
to cool temperatures, should be involved.
Zimmerli and Dick (1996) were the first authors to show that OTA content in
southern wine-growing regions are higher than those of wines from northern areas,
results also supported by the extensive work of Otteneder and Majerus (2000). More
recently, OTA has been detected on grapesproduced in many wine countries, where
the highest amounts of OTA detected in each survey is generally correlated to vines
growing in the warmest regions of each country (Blesa et al. 2006 and Table 11.2).
However, the above-mentioned assumptions were not observed in Australia and
South Africa, where no correlation was found between OTA incidence and wine
region climate (Leong et al. 2006a). This fact was probably due to the rather low
detected levels making these correlations imprecise. Further results in Australia
showed apparently lower incidences in the cooler climate of Tasmania (Hocking
et al. 2007). Canadian wines and grape juices have OTA levels comparable with data
from cold climate wine growing areas in Europe (Ng et al. 2004 and Table 11.2).
The fact that sweet wines from colder regions do not show high levels of OTA in
contrast to those from warmer climates (Valero et al. 2007b) indicates that the main
factor determining the OTA concentration in wines is the contamination of grapes
by toxinogenic moulds.
11.2.5 Prevention and OTA Production Control on Grapes
Given the ubiquity of black aspergilli in vineyards of warm regions, all agents
involved in the wine industry must learn how to live with them, minimising the