Varietal differences in accumulation of ochratoxin A in barley and wheat cultivars after inoculation of Penicillium verrucosum

The natural content of ochratoxin A in grain samples of 6 barley, 2 bread wheat and 1 durum wheat cultivars varied from <0.1 to 0.4 ng/g grain. Samples of the analysed cultivars were surface sterilized and kept in humidity chambers at 20 degrees C and water activity (a(w)) 0.75 or a(w) 0.85 for 8 days. For both environments, the resulting grain equilibrium water content varied between cultivars of both barley and wheat, attributable to agronomic traits. The samples were then inoculated with Penicillium verrucosum and incubated for up to 23 weeks. With time, all cultivars had increasing ochratoxin A content, with maximum content in different barley cultivars ranging from 34 to 630 ng/g grain for a(w) 0.75, and 39 to 260 000 ng/g for a(w) 0.85. Corresponding values for the wheat cultivars were 25 to 2 300 ng/g and 650 to 5 200 ng/g. Significant varietal differences in ochratoxin A accumulation were observed for barley (P < 0.0001), attributable to equilibrium water content, amylose content and natural ochratoxin A; and for wheat (P < 0.0001), attributable to protein content and natural ochratoxin A. Barley 'SW 1306 95/1203' and 'SW 906129 Waxy', and wheat 'SW 39103' accumulated significantly less ochratoxin A than the other cultivars.