Our goal is to analyze spectral imaging data using multiple optical imaging instruments available in USDA-ARS and SafetySpect laboratories to provide analysis along three axes of classification of fish fillets: 1. farm-raised vs. wild-caught species; 2. fresh vs. frozen fillets; 3. Species A vs. Species B targeting most mislabeled fish types in the US market. We are collecting spectral signatures using four imaging systems: (1) Reflectance spectral imaging in the visible and NIR (400-1000 nm), (2) Reflectance spectral imaging in the short wave infra-red (SWIR) (1000-2500 nm), (3) Fluorescence spectral imaging with UVA and violet illumination, (4) Raman imaging with a 785 nm laser excitation. The fish fillet samples were purchased from online vendors. We image with each of the modalities and then freeze, thaw and reimage each fillet (2 cycles of freeze/thaw) to demonstrate effect of freeze/thaw process in the multimode spectral signatures. All fish fillet samples are DNA tested to ensure the species marketed are not mislabeled. We use feature extraction/selection strategy for different modes of measurements based on the measurement physics and biological/chemical characteristics. We analyze different combinations of feature extraction and selection techniques and operate an exhaustive search, optimization, and fusion to find out the most important features using different imaging modes. This process helps identify which imaging mode (or combination) will have the highest impact and yield 95%+ classification accuracy. This optimization procedure will be based on cost function (sensitivity, specificity, area under the curve) from receiver operating characteristics (ROC) curve.
We present a multimode hyperspectral imaging (HIS) system operating in fluorescence and reflectance modes for food quality and safety applications. The system uses spectral band sequential imaging on the detection side. To ensure constant, high S/N levels, the image acquisition time is optimized for each spectral band. The illumination module uses two independent light sources for fluorescence and reflectance measurements, based on three computer-controlled LED illumination rings. UVA (371 nm, FWHM 16nm, power = 91.7mW/cm²) and blue/violet (418 nm, FWHM = 21nm, power = 38.9mW/cm²) LEDs provide fluorescence excitation. White LEDs (power = 35.8mW/cm²) are used for reflectance. The spectral imaging system incorporated within the detection pathway is able to transition between wavelengths within microseconds over the full bandwidth of the device (450 nm - 800 nm). The system is configured as a tabletop platform with both the illumination and detection located above the food sample. Illumination uniformity is ~90%, spatial resolution is 89μm, and spectral resolution is 8nm.
The system was tested for food safety applications by imaging of pet food spiked with Salmonella enterica, where the ability to identify the bacteria in these samples was compared to existing detection methodologies. As an example of food authentication applications, images captured at 75 wavelengths over the range 450 nm to 810 nm with a 5 nm interval were collected from wild salmon and farmed salmon purchased locally. Wild salmon and farmed salmon were found to have distinctly different reflectance features from 515 nm to 650 nm.