Spatial distribution of ochratoxin A in vineyard and sampling design to assess must contamination

The aim of this work was to study the spatial variability of ochratoxin A (OTA) in vineyards and to define a reliable sampling protocol for bunches in order to assess OTA content before harvesting. In 2002, two vineyards with 'Negroamaro' and 'Sangiovese' grape varieties were chosen in Southern Italy. The same sampling design was applied to both vineyards. Ten plants were collected from the X-shaped path of the whole vineyard (plants 1 through 10) and 10 plants from the two central cross-perpendicular lines (plants 11 through 20). Bunches harvested from plants 1 through 10 were numbered progressively, weighed, and crushed separately, and bunches obtained from plants 11 through 20 were crushed plant by plant. Juices obtained were analyzed for OTA content by high-performance liquid chromatography. Then, a simulated approach for sampling was applied, following randomized and systematic designs. High and random variability was observed in OTA content both among bunches and among plants in the two vineyards, independent of contamination level. Simulated sampling design markedly influenced the assessment of must contamination. The best results were obtained when sampling involved one bunch per plant, in a predefined position, from at least 10 plants. Estimated means, obtained with different sampling designs, did not differ significantly from calculated mean OTA content. If the true contamination in a vineyard is 2 microg kg(-1), the limit fixed in Europe for OTA content in must and wine, the range of OTA content assessed sampling one bunch in the central position of 10 plants should lie between 2.9 and 1.4. The accuracy could be considered acceptable.