Ochratoxin A in rice cultivars after inoculation of Penicillium verrucosum

The natural occurrence of ochratoxin A in grain samples of 23 rice cultivars was in the range 0.01-1.0 ng g(-1) rice. Samples from the same cultivars were surface sterilized with NaClO, dried to 19% water content and equilibrated at water activity (a(w)) 0.75 and 20 degrees C for 8 days. Varietal differences in equilibrium w/w water content (p < 0.0001) were found, reflected by differences in amylose and protein contents. Samples were then inoculated with an isolate of Penicillium verrucosum with 1 ml spore suspension to each 50 g rice sample; and incubated at a(w) 0.75 and 20 degrees C for 23 weeks. During incubation, ochratoxin A was accumulated in all cultivars. Significant varietal differences in ochratoxin A accumulation were observed (p < 0.0001). Grain samples with less than 19.5% equilibrium water content accumulated less ochratoxin A (p < 0.005). In a multiple regression analysis accumulated ochratoxin A content was expressed as a function of natural occurrence of ochratoxin A (p < 0.05), equilibrium water content at time of inoculation (p < 0.005), 1000-grain weight (p < 0.1), and chalkiness of endosperm (p < 0.05), with p < 0.0001 for the full function. Naturally occurring ochratoxin A was the strongest independent variable with p < 0.0005 for the slope coefficient in single regression. Rice cultivars IR8, IR24, IR620030-18-2-2 and R91-1081-1 had exceptionally low accumulation of ochratoxin A.