Detecting maize inoculated with toxigenic and atoxigenic fungal strains with fluorescence hyperspectral imagery

Abstract

Naturally occurring Aspergillus flavus strains can be either toxigenic or atoxigenic, indicating their ability to produce aflatoxin or not. The objective was to assess, with the use of a hyperspectral sensor, the difference in fluorescence emission between maize kernels inoculated with toxigenic and atoxigenic inoculums of A. flavus. Maize ears were inoculated with AF13, a toxigenic strain of A. flavus, and AF38, an atoxigenic strain of A. flavus, at dough stage of development and harvested 8 weeks after inoculation. After harvest, single kernels were divided into three groups prior to imaging: control, adjacent, and glowing. Both sides of the kernel, germ and endosperm, were imaged separately using a fluorescence hyperspectral imaging system. After imaging each single kernel was processed with affinity column fluorimetry to determine aflatoxin level. Results from discriminant analysis of the imaging data found that the classification accuracies of the three visually designated groups were not promising. The separation of maize kernels based on different fungal inoculums yielded better results. The best results were achieved with the germ side of the maize kernels. The kernels were later grouped into ‘contaminated’ and ‘healthy’ with 20 ppb and 100 ppb thresholds. The contaminated kernels all had longer peak wavelength than did the healthy ones. Results from the discriminant analysis classification indicated overall higher classification accuracy for the 100 ppb threshold on the germ side (94.4%). The germ side was also more useful at discriminating healthy from contaminated kernels for the 20 ppb threshold.