1. Sensing techniques for food ingredient authentication and food contaminant detection. ARS researchers in Beltsville, Maryland, have developed point-scan and line-scan Raman chemical imaging systems and analysis methods for non-destructive detection of chemical contaminants in powdered food materials. Without any special sample preparation, the newest system can analyze a 30-ml sample (two tablespoons) of dry powder within 10 minutes, more quickly and efficiently than conventional Raman instruments that might require 24 hours to analyze the same sample. The system can perform quantitative contaminant detection down to concentrations as low as 50 parts per million of benzoyl peroxide (used for bleaching) in wheat flour or melamine in milk powder, for example. Currently under patent review, this system will provide a useful screening tool to help detect contaminated food products and prevent their distribution and use, which is now a global concern due to the potential for widespread illnesses and even deaths, such as those that occurred with over 135 documented cases of melamine-adulterated skim milk powder between 1984 and 2012 worldwide.
2. Rapid quantitative detection of benzoyl peroxide in wheat flour. Quality and safety of wheat flour is an important issue worldwide due to the routine use of wheat flour in many staple foods. Use of benzoyl peroxide (BPO), a flour bleaching agent, at levels exceeding regulatory standards can destroy nutrients in the flour and may cause health concerns for consumers. A line-scan high-throughput Raman chemical imaging method was used for direct non-destructive sample analysis to create images visualizing BPO particles that were mixed into samples of wheat flour. BPO was detectable at 50 parts per million, which is on the same level as regulatory standards for acceptable use. High correlation between BPO pixel concentrations in the detection images and BPO mass concentrations in the prepared flour samples suggests that the method can be used for quantitative detection. This Raman imaging inspection method can be used by regulatory agencies and food processors to inspect wheat flour and other food powders and ingredients for adulteration and authentication screening purposes.
3. Detection and quantification of adulterants in milk powder. Past incidents of melamine-contaminated milk have illustrated the grave public health threat posed by economically motivated adulteration of milk. ARS researchers in Beltsville, Maryland, developed a new method for authenticating milk powder, using line-scan Raman chemical imaging to visualize particle identification, spatial distribution, and morphological features of two chemical adulterants (melamine and urea) mixed into milk powder samples, effectively detecting adulterant concentrations as low as 50 parts per million, which is a much lower concentration than those reported in some real-life incidents of adulteration (e.g., thousands of parts per million). The high correlation between the percentages of adulterant pixels in the images and the mass concentrations of the adulterants in the prepared samples suggests that the method can be effectively used for quantitative detection of adulterants in milk powder. This non-destructive Raman method is faster than conventional Raman methods and can be used to help regulatory agencies and food processors authenticate milk powder and other powdered foods subject to economic adulteration or fraud.
4. Subsurface food inspection using line-scan spatially offset Raman spectroscopy technique. Non-destructive subsurface food inspection is challenging due to complex interactions between light and heterogeneous or layered sample materials. ARS researchers in Beltsville, Maryland, developed a new line-scan-based technique to perform spatially offset Raman spectroscopy (SORS) for food and agricultural products. Unlike conventional Raman spectroscopy that detects signals dominated by the material nearest to the sample surface at point of measurement, SORS laterally separates the point laser source and the detector on the sample surface, thereby retrieving subsurface signals in the light that has passed through a deeper region of the sample before reaching the detector. The new line-scan SORS technique is more flexible and efficient than the traditional optical fiber probe approach in that a single image exposure can collect a series of Raman spectra all at once across a broad offset range with a narrow spatial interval. The new technique can be used for rapid and nondestructive subsurface inspection applications such as authentication of food ingredients or detection of contaminants in heterogeneous mixtures and layers or through coatings, films, or plastic packaging, and evaluation of internal attributes of fruits and vegetables, to the benefit of food processors seeking to ensure the safety and quality of their food products as well as regulatory agencies (e.g., FDA and USDA FSIS) that develop and enforce standards of food safety and quality.
5. Fecal detection system for produce fields. A system to take high-resolution visible/near-infrared hyperspectral images in outdoor fields using either natural ambient lighting for reflectance images or a pulsed ultraviolet laser for fluorescence images was designed, built, and tested by ARS researchers in Beltsville, Maryland. Components of the system include a semi-autonomous cart, a gated-intensified camera, a spectral adapter, a frequency-triple Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser, and optics to convert the Gaussian laser beam into a line-illumination source. The laser and camera are mounted on a removable plate that allows for laboratory optics calibration followed by installation on the cart for field use. The front wheels of the cart are independently powered by stepper motors that support stepping or continuous motion. When stepping, a spreadsheet is used to program imaging parameters for each step such as setting acquisition delays, acquisition time, and laser attenuation, a functionality that allows for specialized imaging such as establishing parameters for measuring fluorescence decay-curve characteristics. The system was validated by acquiring images of fluorescence responses of spinach leaves and dairy manure. These developments can be incorporated into future field imaging systems to detect fecal contamination and prevent cross-contamination during harvest operations.
6. Identification of parasite membrane vulnerability for chemical water treatments. Bleach is a commonly used disinfectant but can be ineffective in killing the infectious parasite Cryptosportium parva, which sickened ten school children in Litchfield, Minnesota, in May 2016. This parasite can cause typically mild yet treatable illness as well as severe and even fatal illness in people with weakened immune systems, and can easily be spread by contaminated drinking water or recreational aquatic environments. Raman mapping of the parasite’s protective membrane layer in its environmentally durable oocyst life stage found significant concentrations of calcium ions and magnesium ions on the oocyst’s spherical surface and at the edges of opened / broken surfaces. This suggests chemical mechanisms to be investigated for effective water treatment to protect against and prevent future outbreaks.
7. Fluorescence imaging for detecting fecal contamination of soil and assessing compost maturity. Serious outbreaks of food-borne illness can result from consumption of fresh produce contaminated by pathogens such as E. coli and salmonella that originate from animal or human fecal matter, particularly if the produce is mishandled at temperatures that encourage pathogen growth. Sources/pathways of contamination can include the excrement of wildlife or livestock, immature manure composts used as soil amendments, contaminated irrigation water or field tools, and poor health or hygiene of field workers. Although food safety standards exist regarding use of mature manure composts and prevention of fecal contamination in produce fields, verification in field production environments remains challenging since neither compost maturity nor fecal traces are easily identified by eye. ARS researchers investigated hyperspectral fluorescence imaging techniques to determine spectral characteristics of fecal samples from four species (dairy cows, pigs, chickens, and sheep) to test detection of animal feces and identification of species origin in soil-feces mixtures, and to evaluate use for assessing maturity of manure-based composts and results found fluorescence features that could be used to detect feces on soil and showed that identifying animal species origin is feasible. Furthermore, the fluorescence features could be used via simpler single-waveband imaging techniques, instead of more complex and costly full-spectrum hyperspectral imaging methods, for assessing compost maturity. These findings can be incorporated into field-use tools to help prevent contamination or harvesting of contaminated produce.
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Dhakal, S., Chao, K., Qin, J., Kim, M.S., Chan, D.E. 2017. Identification and evaluation of composition in food powder using point-scan Raman spectral imaging. Applied Sciences. 7(1):1.
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Chen, Z., Peng, Y., Li, Y., Chao, K. 2017. Extraction and identification of mixed pesticides’ Raman signal and establishment of their prediction models. Raman Spectroscopy. 48(3):494-500.
Schmidt, W.F., Hapeman, C.J., McConnell, L., Mookherji, S., Rice, C., Nguyen, J.K., Qin, J., Chao, K., Kim, M.S., Broadhurst, C.L., Shelton, D.R. 2017. Using torsional forces to explain the gradient temperature Raman spectra of endosulfan isomers and its irreversible isomerization. Journal of Molecular Spectroscopy. 1139:43-51.
Broadhurst, L., Schmidt, W.F., Kim, M.S., Nguyen, J.K., Qin, J., Chao, K., Bauchan, G.R., Shelton, D.R. 2016. Continuous gradient temperature Raman spectroscopy of n-6 DPA and DHA from -100 C to 20°C. Chemistry and Physics of Lipids. 200:1-10.
Mo, C., Kim, M.S., Kim, G., Lim, J., Delwiche, S.R., Chao, K., Lee, H., Cho, B. 2017. Spatial assessment of soluble solid contents on apple slices using hyperspectral imaging. Biosystems Engineering. 159:10-21.
Cho, H., Lee, H., Kim, S., Kim, D., Park, H., Lefcourt, A.M., Chan, D.E., Kim, M.S. 2016. Hyperspectral fluorescence imaging of animal feces and soil: potential use of fluorescence imaging for assessment of soil fecal contamination and compost maturity. Applied Sciences. 6:246.
Everard, C., Kim, M.S., O'Donnell, C. 2016. Distinguishing bovine fecal matter on spinach leaves using field spectroscopy. Applied Sciences. 6:246-254.
Mo, C., Kim, K., Kim, M.S., Lim, J., Lee, K., Lee, W., Cho, B. 2017. On-line fresh-cut lettuce quality measurement system using hyperspectral imaging. Biosystems Engineering. 156:38-50.
Mo, C., Kim, G., Kim, M.S., Lim, J., Lee, S.H., Lee, H., Kang, J., Cho, B. 2017. Discrimination methods of biological contamination on fresh-cut lettuce based on VNIR and NIR hyperspectral imaging. Infrared Physics and Technology. 85:1-12.
Mo, C., Kim, G., Kim, M.S., Lim, J., Cho, H., Barnaby, J.Y., Cho, B. 2017. Fluorescence hyperspectral imaging technique for the foreign substance detection on fresh-cut lettuce. Journal of the Science of Food and Agriculture. 97(12):3985-3993.
Qin, J., Chao, K., Schmidt, W.F., Dhakal, S., Cho, B., Peng, Y., Huang, M., Lee, H., Kim, M.S. 2017. Subsurface inspection of food safety and quality using line-scan spatially offset Raman spectroscopy technique. Food Control. 75:246-254.
Qin, J., Kim, M.S., Chao, K., Chan, D.E., Delwiche, S.R., Cho, B. 2017. Line-scan hyperspectral imaging techniques for food and agricultural applications. Applied Sciences. 7(20):125.
Qin, J., Kim, M.S., Chao, K., Dhakal, S., Lee, H., Cho, B. 2017. Detection and quantification of adulterants in milk powder using high-throughput Raman chemical imaging technique. Food Additives & Contaminants. 34(2):152-161.
Lohumi, S., Joshi, R., Kandpal, L.M., Kim, M.S., Cho, H., Mo, C., Seo, Y., Rahman, A., Cho, B. 2017. Quantitative analysis of Sudan dye adulteration in paprika powder using FTIR spectroscopy. Journal of Food Additives & Contaminants. 34(5):678-686.
Scholl, P., Bergana, M., Yakes, B., Zbylut, S., Downey, G., Mossoba, M., Jablonski, J., Margaletta, R., Holroyd, S.E., Buehler, M., Qin, J., Xie, Z., Hurst, W., Laponte, J.H., Roberts, D., Zrybko, C., Mackey, A., Holton, J.D., Israelson, G.A., Payne, A., Kim, M.S., Chao, K., Moore, J. 2017. Effects of the adulteration technique on the near-infrared detection of melamine in milk powder. Journal of Agricultural and Food Chemistry. 65:5799-5809.
Lefcourt, A.M., Kistler, R., Gadsden, A., Kim, M.S. 2016. Automated cart with VIS/NIR hyperspectral reflectance and fluorescence imaging capabilities. Applied Sciences. 7(1):3.
Qin, J., Kim, M.S., Chao, K., Cho, B. 2017. Raman chemical imaging technology for food and agricultural applications. Journal of Biosystems Engineering. 42(3):170-189.
Lohumi, S., Kim, M.S., Qin, J., Cho, B. 2017. Raman imaging from microscopy to macroscopy: Quality and safety control of biological materials. Trends in Analytical Chemistry. 93:183-198.