Spatio-temporal patterns of Aspergillus flavus infection and aflatoxin B1 biosynthesis on maize kernels probed by SWIR hyperspectral imaging and synchrotron FTIR microspectroscopy

Authors: YAO, LU - China Agricultural University; BEIBEI, JIA - Chinese Academy Of Inspection And Quarantine; Yoon, Seung-Chul; Zhuang, Hong; Ni, Xinzhi; Guo, Baozhu; Gold, Scott; FOUNTAIN, JAKE - Mississippi State University; Glenn, Anthony - Tony; Lawrence, Kurt; ZHANG, HAICHENG - China Agricultural University; GUO, XIAOHUAN - China Agricultural University; ZHANG, FENG - Chinese Academy Of Inspection And Quarantine; WANG, WEI - China Agricultural University

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2022
Publication Date: 2/3/2022
Citation: Yao, L., Beibei, J., Yoon, S.C., Zhuang, H., Ni, X., Guo, B., Gold, S.E., Fountain, J.C., Glenn, A.E., Lawrence, K.C., Zhang, H., Guo, X., Zhang, F., Wang, W. 2022. Spatio-temporal patterns of Aspergillus flavus infection and aflatoxin B1 biosynthesis on maize kernels probed by SWIR hyperspectral imaging and synchrotron FTIR microspectroscopy. Food Chemistry. 382:132340. https://doi.org/10.1016/j.foodchem.2022.132340.
DOI: https://doi.org/10.1016/j.foodchem.2022.132340

Interpretive Summary: Aspergillus flavus, a toxin-producing fungus, can infect many important agricultural crops, such as corn and peanut, and cause disease by producing a significant amount of toxic compounds, called aflatoxins. Crops infected with A. flavus pose a great threat to food safety and human health. Hence, there is a need for research on development of technology for rapid, high-throughput, and non-destructive detection and sorting of contaminated grains at post-harvest, prior to grain storage and processing. In this study, macroscopic and microscopic chemical imaging techniques were combined to characterize chemical and topographic changes of A. flavus infection and aflatoxin B1 (AFB1) biosynthesis and accumulation in corn kernels over 4 days. Shortwave infrared hyperspectral imaging (SWIR-HSI) in the wavelengths from 1,000 nm to 2,500 nm was used to investigate the spectral features of a nutrient loss and the AFB1 accumulation from the process of A. flavus invasion into corn kernels with different level of exterior damage. In addition, synchrotron radiation-based Fourier-transform infrared (SR-FTIR) micro-spectroscopy was coupled with two-dimensional correlation spectroscopy (2DCOS) to study the nutrient loss and changes in kernel structure and composition during the fungal infection. The study results showed that the spatio-temporal patterns of fungal infection on damaged corn kernels could be detected with a combination of macro SWIR-HSI and micro SR-FTIR and 2DCOS .

Technical Abstract: Aspergillus flavus, a toxin-producing fungus and its toxic metabolites-aflatoxins can infect and contaminate maize kernels, thus posing a great threat to food safety and human health. However, the interactive mechanism of A. flavus growth and aflatoxin B1 (AFB1) accumulation and nutrient loss in maize kernels remains unclear. In this study, macroscopic and microscopic chemical imaging techniques were combined to understand chemical and topographic changes of A. flavus infection and AFB1 biosynthesis and accumulation in maize kernels. To study the effect of the chemical topographic changes, maize kernels were artificially damaged to produce intact, pierced and halved kernels, which were then inoculated with A. flavus and cultivated for 4 days at a 24-h time interval. Shortwave infrared hyperspectral imaging (SWIR-HSI) was employed to extract the spectral information of a kernel nutrient loss and the AFB1 accumulation from the process of A. flavus invading the maize kernels with an incremental damage. The partial least squares regression (PLSR) methods were used to quantitatively predict the AFB1 level with the full spectral information (R2v = 0.90, RMSEV = 3.636 and RPD = 2.44) and the partial spectral information in only ten key wavelengths (R2v = 0.89, RMSEV = 3.370 and RPD = 2.48). Then the spatial distribution of AFB1 on a single kernel was qualitatively evaluated. Furthermore, synchrotron radiation-based Fourier-transform infrared (SR-FTIR) micro-spectroscopy coupled with two-dimensional correlation spectroscopy (2DCOS) was utilized to explain the nutrient loss, the changes in kernel structure and composition during the fungal infection. The halved-kernel samples with a significant intra-group discrepancy was examined. The study finding showed that, as the fungal infection time became longer, the nutrient structures such as lipid (2926 cm-1), protein (1650 cm-1) and starch (1025 cm-1) in maize kernels were gradually hydrolyzed and then the trace AFB1 (1733, 1361 cm-1) was produced. The results were visualized through the SR-FTIR chemical mapping images. In conclusion, the combination of the SWIR-HSI technique with a high spectral resolution and SR-FTIR micro-spectroscopy technology with a high spatial resolution complementarily provided new insights on how to quantify the spatio-temporal patterns of fungal infection on artificially wounded maize kernels with the information of molecular vibrations and functional groups of variety components caused by the infection.