Deep Learning-Enhanced Hyperspectral Imaging for Non-Destructive Detection of Early-Stage Fungal Contamination in Stored Wheat Grain
Abstract
Post-harvest fungal contamination of stored wheat grain, predominantly by Fusarium, Aspergillus, and Penicillium species, causes substantial economic loss through grain spoilage and mycotoxin-related batch rejection, yet conventional quality control relies on visual inspection and laboratory mycotoxin assays that detect contamination only after it has progressed to a visibly or chemically advanced stage. This study addresses the resulting food-safety and agricultural-engineering gap by developing and validating a deep learning framework that processes hyperspectral imaging (HSI) data to detect fungal infection in wheat kernels substantially earlier than visible symptoms or mycotoxin thresholds would permit, integrating optical sensing engineering, food microbiology, and computer vision methods within a single non-destructive screening system.
Wheat kernels (cultivar HD-3086) were inoculated with Fusarium graminearum, Aspergillus flavus, and Penicillium spp. under controlled storage conditions (28°C, 85% relative humidity) and imaged daily across a push-broom hyperspectral imaging system spanning 400-1000 nm (240 spectral bands) over a 14-day storage trial, with parallel deoxynivalenol (DON) mycotoxin quantification by enzyme-linked immunosorbent assay providing ground-truth contamination severity labels. A three-dimensional convolutional neural network (3D-CNN) jointly exploiting spectral and spatial kernel-surface information was trained for four-class infection severity classification (healthy, early-stage, moderate, severe) and benchmarked against a 2D-CNN (spectral features only), partial least squares discriminant analysis (PLS-DA), and a support vector machine, using a dataset of 5,600 individually imaged and ground-truth-labelled kernels.
The 3D-CNN achieved 95.7% four-class classification accuracy and area-under-curve values of 0.911-0.971 for binary infection detection across the three fungal species, exceeding the 2D-CNN (91.8% accuracy) and classical baselines (82.3-84.6% accuracy). Critically, the HSI-CNN system detected infection with 50% cumulative detection probability by storage day 3.2, compared to day 8.5 for simulated visual inspection thresholds, a 5.5-day earlier detection window that precedes the steep phase of deoxynivalenol accumulation entirely. Saliency-based wavelength importance analysis identified the 680 nm chlorophyll-absorption band and the 700 nm red-edge transition as the two most discriminative spectral features, consistent with established plant-pathology mechanisms linking fungal infection to pigment degradation. Economic analysis indicates that HSI-CNN continuous screening reduces annualised per-tonne storage losses by 71.9% relative to no monitoring and by 56.8% relative to periodic visual inspection. These findings demonstrate that coupling optical sensing engineering with deep learning-based spectral-spatial analysis provides a viable non-destructive early-warning system for grain storage quality management.
Keywords: hyperspectral imaging, deep learning, convolutional neural network, fungal contamination, wheat grain, mycotoxin, food safety, post-harvest, non-destructive sensing, precision agriculture
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