Temporal effects on internal fluorescence emissions associated with aflatoxin contamination from corn kernel cross-sections inoculated with toxigenic and atoxigenic Aspergillus flavus

Authors: HRUSKA, ZUZANA - Mississippi State University; YAO, HAIBO - Mississippi State University; KINCAID, RUSSELL - Mississippi State University; Brown, Robert; Bhatnagar, Deepak; Cleveland, Thomas

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2017
Publication Date: 9/15/2017
Citation: Hruska, Z., Yao, H., Kincaid, R., Brown, R.L., Bhatnagar, D., Cleveland, T.E. 2017. Temporal effects on internal fluorescence emissions associated with aflatoxin contamination from corn kernel cross-sections inoculated with toxigenic and atoxigenic Aspergillus flavus. Frontiers in Microbiology. 8:1718. https://doi.org/10.3389/fmicb.2017.01718.
DOI: https://doi.org/10.3389/fmicb.2017.01718

Interpretive Summary: Non-invasive, easy to use and cost-effective spectral technology offers a valuable alternative for rapid detection of aflatoxins. Fluorescence hyperspectral imaging, in particular, offers a potential rapid and non-invasive method for detecting the presence of aflatoxins in corn infected with the aflatoxin producing fungus Aspergillus flavus (A. flavus). Earlier studies have shown that whole corn kernels contaminated with aflatoxins exhibit different spectral signatures (fluorescence peaks of contaminated kernels shifted to higher wavelengths) from uncontaminated kernels based on the external fluorescence emission of the whole kernels. The present study examined the internal fluorescence spectral emissions from cross sections of kernels infected with toxigenic (toxin producing) and atoxigenic (non producing) A. flavus in order to separate the two fungal strains from each other and detect the aflatoxin signal. Although results indicate no difference in peak shift between the toxigenic A. flavus from the atoxigenic, there was a marked difference in fluorescence intensity seen on different days between the two strains, which may be a useful indicator of the location of aflatoxin contamination. The ability of successfully separating corn kernels contaminated with toxigenic from atoxigenic fungi based on spectra, would benefit the grain industry, particularly the growers and exporters.

Technical Abstract: Non-invasive, easy to use and cost-effective technology offers a valuable alternative for rapid detection of carcinogenic fungal metabolites, namely aflatoxins, in commodities. One relatively recent development in this area is the use of spectral technology. Fluorescence hyperspectral imaging, in particular, offers a potential rapid and non-invasive method for detecting the presence of aflatoxins in maize infected with the toxigenic fungus Aspergillus flavus. Earlier studies have shown that whole maize kernels contaminated with aflatoxins exhibit different spectral signatures from uncontaminated kernels based on the external fluorescence emission of the whole kernels. Here, the effect of time on the internal fluorescence spectral emissions from cross sections of kernels infected with toxigenic and atoxigenic A. flavus, were examined in order to eliminate the possibility that any differential signal was due to the presence of fungus and not strictly due to the presence of aflatoxin. First, the difference in internal fluorescence emissions between cross-sections of kernels incubated in toxigenic and atoxigenic inoculum was assessed. Kernels were inoculated with AF13 and AF36 for 5, 7, and 9 days before cross-sectioning and imaging. There were 180 kernels (360 halves) imaged, including controls. Second, in a different set of kernels (15 kernels/group; 135 total), the germ of each kernel was separated from the endosperm to determine the major areas of aflatoxin accumulation and progression over nine growth days. Kernels were inoculated with AF13 (toxigenic) and AF36 (non-toxigenic) fungal strains for 5, 7, and 9 days before the endosperm and germ were separated, followed by fluorescence hyperspectral imaging and chemical aflatoxin determination, respectively. The results indicate that, although there was no discernible difference between the aflatoxin producing A. flavus from the non-producing strain in maize cross-sections on the basis of a fluorescence peak shift, the marked difference in fluorescence intensity seen on different days between the two strains, may be a useful indicator of the location of aflatoxin contamination. Results also reveal a possible preferential difference in the internal colonization of maize kernels between the toxigenic and atoxigenic strains of A. flavus suggesting a potential window for differentiating the strains based on fluorescence spectra at different time points.