Aflatoxins and fluorescence in Brazil nuts and pistachio nuts

Brazil nut and pistachio nut samples from lots known to be contaminated with aflatoxins were visually inspected in detail. Kernels were split lengthwise in halves, and internally highly discolored kernels were analyzed individually. Highly contaminated Brazil nut kernels showed yellow fluorescence if illuminated with light at 360nm. However, not all fluorescent kernels were contaminated with aflatoxins, and brown spotted kernels also contained these toxins. While contaminated Brazil nut kernels showed different appearance, only brown or brown spotted pistachio kernels were highly contaminated with aflatoxins. In yellowish fluorescent pistachio kernels no aflatoxins, citrinin, kojic acid, patulin, or ochratoxin A could be detected (detection limits: 10-100 microgram/kg, 0.5-1, 40-50, 0.2-0.5, and 0.1-0.3mg/kg, respectively). Slightly discolored kernels and sound kernels were analyzed in different batches. In this way it was shown that contaminated kernels were internally discolored. Ratios of 4700 uncontaminated kernels to 1 kernel containing aflatoxin B1 and 4300 to 1, respectively, were calculated for two pistachio nut samples from different lots. A similar ratio for Brazil nuts could not be calculated since not all highly contaminated kernels were analyzed individually. The highest aflatoxin B1 concentration in a pistachio kernel was 1400 mg/kg; in a Brazil nut 4 mg/kg aflatoxin B1 and 1.2 mg/kg aflatoxin G1 were detected. The high aflatoxin concentrations in a few kernels indicate that the usual sampling sizes of 20 and 50 lb (Brazil nuts and pistachio nuts, lots 200 bags and 75 000 lb, respectively) may not be sufficient