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Raman spectroscopy (RS) is a highly versatile and dynamic spectroscopy method that can be used to perform both the qualitative and quantitative analysis for a wide range of samples. During RS analysis, a high-energy laser light is exposed to a sample, which will absorb and emit a certain amount of scattered light in the form of incident photons. When used for qualitative purposes, RS is used to measure the frequency of the scattered photons, whereas quantitative analysis of a sample is achieved by measuring the intensity of the scattered photons1. Some of the most common applications of RS include the analysis of forensic samples, drugs of abuse and carbon materials, as well as various samples in the pharmaceutical, cosmetic, biological and geological industries2. The use of RS within the food and beverage industry has been widely used for characterization purposes and evaluating the safety and quality attributes for a broad range of food and agricultural products.
Detecting Pesticides and Fungicides in Food with RS
As consumers continue to become more aware of potential contaminants entering their food and beverage products, researchers have investigated more sensitive techniques that can accurately detect pesticides, fungicides, herbicides and other unwanted chemicals present in these products. To this end, a 2013 study combined surface-enhanced Raman spectroscopy (SERS) technology with gold-coated SERS-active nanosubstrates to detect and characterize pesticides that were extracted from the surfaces of apples and tomatoes3. Lin and colleagues found that their detection method was able to meet maximum residue limits that have been established by the Food and Agriculture Organization of the United Nations and the World Health Organization. In conclusion, the use of SERS coupled with SERS-active nanosubstrates was determined to be a rapid, sensitive and highly reliable for detecting and characterizing chemical contaminants present in food samples3.
The utilization of SERS for the presence of contaminants in food was further investigated in a 2018 study that involved multiple Raman spectra using gold nanoparticles as surface enhancers, rather than the previous study that only used a single Raman spectrum. These researchers found that Raman shifts of 413, 346 and 634 cm-1 provided useful information regarding the distribution of pesticide residues on the surface of the tested agricultural products4.
Bacterial Identification by RS
Various studies have been published utilizing SERS as a method to characterize, discriminate and identify various microorganisms in food products, as well as the ways in which these microorganisms respond to both abiotic and biotic stress. To this end, Fan and colleagues utilized SERS coupled with silver nanosubstrates to detect the presence of Escherichia coli (E. coli), Staphylococcus epidermis, Listeria monocytogenes, and Enterococcus faecalis in various sample types. In their methods, the silver nanoparticles were deposited into the bacteria intracellularly by exposing the samples to silver nitrate and sodium borohydride solutions. SERS spectra were then obtained from two to three drops of the treated bacteria cells5. These researchers found that SERS served as a useful analytical technique that accurately classified the different bacteria species present within mixed samples.
Over the past decade, a significant amount of research has found that Raman analysis on food and beverage products such as fruits, vegetables, meats, grains, food powders, and oils, is a highly reliable technique. As Raman instrumentation, as well as the spectral and imaging data analysis techniques that often accompany this method, continue to advance, the industrial application of this technology may be a realistic option in the near future.
- Bambrah, G. S., & Sharma, R. M. (2016). Raman spectroscopy – Basic principle, instrumentation and selected applications for the characterization of drugs of abuse. Egyptian Journal of Forensic Sciences 6(3), 209-215. DOI: 10.1016/j.efs.2015.06.001.
- “Raman spectroscopy, principles and applications” – Nwaji Njemuwa (Rhodes University)
- Zhou, B. L., Liu, X., Sum, X., Li, H., & Lin, M. (2013). Detection of Pesticides in Fruits by Surface-Enhanced Raman Spectroscopy Coupled with Gold Nanostructures. Food and Bioprocess Technology 6(3), 710-718. DOI: 10.1007/s11947-011-0774-5.
- Chen, J., Dong, D., & Ye, S. (2018). Detection of pesticide residue distribution on fruit surfaces using surface-enhanced Raman spectroscopy imaging. RSC Advances 9, 4726-4730. DOI: 10.1039/C7RA11927E.
- Fan, C., Hu, Z., Mustapha, A., & Lin, M. (2011). Rapid detection of food- and waterborne bacteria using surface-enhanced Raman spectroscopy coupled with silver nanosubstrates. Applied Microbiology Biotechnology 92(5); 1053-1061. DOI: 10.1007/s00253-011-3634-3.