Multispectral fluorescence imaging for detection of bovine faeces on Romaine lettuce and baby spinach leaves

• Observable shift in leaf chlorophyll and faecal chlorophyll fluorescence emissions.
• Multispectral fluorescence imaging method was developed for faecal detection.
• Two-band ratio imaging detected all faecal spots on lettuce and spinach samples.
• Potential use in online food safety inspection for processing of fresh greens.

Hyperspectral fluorescence imaging with ultraviolet-A excitation was used to evaluate the feasibility of two-waveband fluorescence algorithms for the detection of bovine faecal contaminants on the abaxial and adaxial surfaces of Romaine lettuce and baby spinach leaves. Correlation analysis was used to select the most significant waveband pairs for two-band ratio and difference methods in distinguishing contaminated and uncontaminated leaf areas. For this investigation, two-band ratios using bands at 665.6 nm and 680.0 nm (F665.6/F680.0) for lettuce and at 660.8 nm and 680.0 nm (F660.8/F680.0) for spinach effectively differentiated all contamination spots applied to the lettuce and spinach leaves, respectively. The fluorescence emission peaks for the faecal matter of animals that consume green plant materials and for chlorophyll a occur in close proximity in the red spectral region. Consequently, a high spectral resolution would be required for multispectral imaging with these two-band ratios for online implementation to detect bovine faecal contamination on leafy greens such as Romaine lettuce and baby spinach.