Paola Battilani

Abstract

Ochratoxin A has been frequently detected in grapes and its derived products since 1996, with contamination limits fixed by the European Commission for dried vine fruits, wine and grape juice to protect consumers. Ochratoxin A is produced in vineyards, primarily by Aspergillus carbonarius. Meteorological conditions are a major factor in determining risk areas and years. The cropping system also can significantly influence the final toxin content in bunches. Ochratoxin A can increase post harvest, during drying or standing before crushing, but this toxin is not synthesized during wine making.

Introduction

Mycotoxins, as toxic secondary metabolites produced by fungi, have been known since 1960 when aflatoxin was first described, but their effects have been studied in depth only since 1970. Ochratoxins were first isolated from Aspergillus ochraceus in 1965 and were named after the producing fungus. There are three main ochratoxins, A, B and C, that differ slightly in structure, but ochratoxin A is considered the only true toxin. Both A. ochraceus and Penicillium verrucosum are known to synthesize ochratoxin A in cereals (CAST, 2003). Ochratoxin A was first reported in wine and grape juice in 1996 by Zimmerli and Dick (1996). They suggested that processed grape products might be sources of the toxin in human diets and confirmed their hypothesis through a survey of products from Swiss markets. Many additional surveys followed, mainly in Europe, which confirmed that ochratox-in A was a problem in Southern Europe in rosé and red wines, and to a lesser extent in white wine (reviewed in Battilani et al., 2004b).

Ochratoxin A was detected in all of the surveys, but the incidence of contaminated samples varied widely. The maximum ochratoxin A level reported for red wine was > 3 |g/l in countries such as Spain (Bellí et al., 2004a; Blesa et al., 2004), Italy and Morocco (reviewed in Battilani et al., 2004b). The year of grape production and the associated meteorological conditions always were relevant as was latitude; higher latitudes generally were associated with lower ochratoxin A content (Battilani et al., 2004b; Fig. 1).

Ochratoxin
Figure 1. Mean ochratoxin A content (ng/l) in white, rosé and red wines sampled in different countries in the Mediterranean basin. Bars represent the mean value and numbers the maximum value reported (after Battilani et al., 2004b).

Red wine and grape juice had higher contamination levels, > 5 |g/l, as did dried vine fruits, e.g., currants contained up to 53 ng/g of ochratoxin A as did balsamic vinegar at levels up to 4.3 |g/l (Battilani et al., 2004b; Table 1). The presence of ochratoxin A in grapes and products derived from them was confirmed in studies aimed at identifying the factors related to its production and ensuring compliance with European Commission regulation 466/2001 for dried vine fruits (10 ng/g) and regulation 123/2005 for wine and grape juice (2 |g/l).

Fungi responsible for the production of ochratoxin A in grapes

The first studies of ochratoxin A in grapes and wine evaluated fungi known to produce ochratoxin A in cereals that also were found in grapes. Subsequent surveys, however, shifted this focus. Aspergillus section Nigri, the "black Aspergilli", includes all of the fungi responsible for ochratoxin A production in grapes (Battilani and Pietri, 2002; da Rocha Rosa et al., 2002; Sage et al., 2002), but A. ochraceus was detected occasionally and at a relatively low incidence (Battilani et al., 2003b; Belli et al, 2006).

Table 1. Maximum reported levels of ochratoxin A (ng/g) in grape juice, vinegar and dried vine (Battilani et al., 2004b).

Product Type

Ochratoxin A

Grape juice White

Vinegar White and Red

Balsamic Dried vine Currant

Sultana Raisin

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