Evaluation of growth characteristics of a mixed culture of toxigenic fungi by Visible/Near-infrared hyperspectral imaging

Abstract. Visible/near-infrared (VIS/NIR) hyperspectral imaging (400-1000 nm) was applied to evaluate the growth characteristics of a mixed culture of A. niger, A. flavus, A. parasiticus, A. glaucus and Penicillium. The hyperspectral images of the five fungi growing on rose bengal medium and maize meal medium were recorded daily for 6 days. The experiment was carried out in two parts according to the inoculation method i.e. point inoculation (part A) and spreading inoculation (part B). In both experiments on both media, the rapid expansion of A. niger can be observed during the culture period. Principle component analysis (PCA) was performed on the cleaned hyperspectral images. Average spectra of each fungus in each growth day were extracted, and then PCA and Linear Discriminant Analysis (LDA) were applied on the full spectral range. In part A of the experiment, the PCA-DA classification result of fungal growth days was moderate and for RBA the accuracy for calibration was 58%, validation was 58%; for MMA the calibration accuracy was 45% and validation, 44%. Classification result of growth days by PCA-DA for experiment B were 100% for calibration and validation for RBA, whereas for MMA, calibration accuracy reached 98% and validation accuracy was 95%. It can be concluded that whichever method of inoculation used whether point or spreading inoculation, the fastest growing fungi such as Aspergillus niger in the mixed culture will dominate the rest of the fungi with low to moderate growth patterns.