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Many of us have spent more time in the kitchen in the past year than usual, (re)discovering our culinary skills with varying degrees of success. Our pantries have been kept full, and our stoves on for a year (and counting) since our normal, social ways of life have been curtailed by home office regulations, online schooling, and the sweeping closures of bars and restaurants.
Cooking at home can mean a number of things. Some people rely on «Chef Mike» (i.e., the microwave) to prepare their meals, while others turn humble ingredients into haute cuisine dishes. However, most people would probably agree that the keys to delicious and nutritious meals are fresh, high quality ingredients.
What is on your menu today? For breakfast, perhaps toast and some fresh pressed orange juice, lunch is maybe a quiche with tomatoes and cheese, and for dinner, stir-fried vegetables accompanied by a glass of good wine. Hungry yet?
With all of this talk about food, how can you be certain that the ingredients you are using in the kitchen are of the highest quality? You may trust in the grocery store, the brand, or the farmer at your local market, but do you know how different food quality parameters are measured?
One technique provides rapid, non-destructive and specific food quality testing: Raman spectroscopy. Whether you are looking to determine the ripeness of fruits or vegetables, the adulteration of spices or dairy products, or contamination of foods with banned pesticides, Raman spectroscopy is at the cutting edge of food quality analysis.
If you want to refresh your knowledge about Raman spectroscopy, have a look at our previous blog post about MIRA, which includes some history about the technique.
To learn more about the analysis of trace adulterants in foods and beverages, read our blog post all about measurement with SERS (surface‐enhanced Raman scattering).
Are you confused about the differences between Raman spectroscopy and SERS? You’re not alone! Check out our blog post about these two techniques and learn about their benefits.
Raman vs SERS… What’s the Difference?
Here, we share a selection of peer-reviewed articles from the scientific community using Raman spectroscopy and portable instrumentation from B&W Tek, a Metrohm Group Company and Metrohm Raman to address quality issues of food. Enjoy your meal! Bon appetit!
Starter
To begin, maybe you would be interested in sharing a bottle of red wine with your companion as you snack on some crispy bread sticks. Red wines are made from red varieties of grapes, whose color is imparted through the crushing process as the skins soak in the sugary juices. Phenolic compounds derived from the grape skins can be beneficial to human health, and can be determined with Raman spectroscopy [1].
It’s not only beneficial compounds but also harmful contaminants that can be measured in beverages with Raman spectroscopy. Fungicides can also be detected in wine with SERS.
Download our free Application Note if you want to find out more.
Watch our video below to see how methanol in alcoholic drinks is quantified rapidly without sample preparation – right at the bottle!
Snacking on prepackaged foods when you are on the go, or when you don’t feel like cooking at the moment, is something we have all done. The moisture levels in most of these foods is kept to a minimum, especially in those meant to have long shelf lives. Water content above certain levels allows harmful bacteria to grow, which is one of the major reasons to always consult the date of packaged foods before consumption. Eating contaminated foods can cause severe sickness and even death. It is possible to determine whether such low moisture foods (LMFs) contain harmful levels of these bacteria with SERS [2].
What else do both of these applications have in common? Both of them utilize the portable i-Raman Plus instrument from B&W Tek. For more information, download our free Application Note below.
Portable Raman for Quantification of Methanol in Contaminated Spirits
Main Course
Depending on what you are in the mood for, anything is possible. Some tomatoes, vegetables, spices, perhaps meat (if you eat it) and a starch are on the menu today, ready to be turned into almost any dish.
Determining whether fresh foods are at peak ripeness can be a tricky process, not necessarily just the change of a color. The ripeness of a fruit or vegetable indicates its antioxidant content, as well as nutrients and other beneficial compounds. Monitoring the ripening process is possible with portable Raman spectroscopy [3], such as the B&W Tek i-Raman Pro.
Some of us like a little heat in our meals. Unfortunately, the adulteration of spices like chili powder (sometimes known as cayenne powder) is common, as cheap and harmful coloring agents are added to achieve more profits at the cost of human health. These synthetic dyes are able to be determined easily even at trace levels with SERS [4].
Download our free Application Note here to learn more about the detection of trace levels of Rhodamine B in cayenne powder with SERS.
Some types of cheese command a high price for what seems like just a small pinch. One such type is Parmigiano Reggiano, an Italian cheese with a protected denomination of origin (PDO) quality marker, made in compliance with several production rules. These cheeses are subject to counterfeiting, but luckily this is easy to determine on-site without damaging the sample using handheld Raman spectroscopy [5].
The price of meat varies according to several reasons, even for the same animal source, section (cut), and portion size. Among these is the origin of the meat, as well as how it was produced (e.g., organic or a factory farm). Determining the difference between premium meat products and lower quality ones is possible with handheld Raman systems [6] such as MIRA from Metrohm Raman. Not only these differences but also the freshness of meat during the production process can be measured with portable Raman devices [7] like the i-Raman Plus from B&W Tek.
Using lower quality cooking oil with a low smoke point at high temperatures can result in consumption of harmful byproducts formed during cooking. Older oils have a lower antioxidant content as a result of the aging process, and can become rancid when the antioxidant properties vanish. For these reasons, high quality edible oils full of antioxidants are worth much more, but are also susceptible to adulteration with cheaper ingredients. It is possible to not only determine the purity of edible oils by Raman spectroscopy [8] but also the heat stability of different types of oils [9].
For more information about the analysis of edible oils by Raman spectroscopy, download our free Application Notes and our White Paper below!
Fast Ingredient Analysis of Edible Oils Using a Portable Raman Spectrometer
Trace Detection of Fenthion in Olive Oil with MISA
White Paper: Facile Verification of Edible Oils with Raman Spectroscopy
Dessert
After dinner is over, a hot beverage like tea can be nice to cleanse the palate. How can you be sure that the tea is free of banned pesticides, other than buying from a trusted organic label? SERS allows rapid identification of such substances in tea leaves [10].
To learn more about detecting illegal compounds such as herbicides on tea leaves, download our free Application Note here.
The honey you put in your tea or drizzle over your dessert can also be subjected to tampering. Depending on the type of flower or the origin of the honey, costs can vary widely for the same volume. Some honeys (e.g., Manuka) claim to impart certain health benefits, and therefore many lower quality products with cheap sweeteners (e.g., high fructose corn syrup) are falsely labeled as such and sold at a higher price point to unsuspecting consumers. It is possible to detect honey adulteration [11] and even its botanical origin [12] with Raman spectroscopy.
Not only tea and honey, but also coffee and the milk added to it can be analyzed with Raman spectroscopy to determine various quality markers and adulterants.
The protein content of milk can be falsely enhanced with the addition of melamine. This compound is now monitored in dairy products due to scandals which led to deaths from kidney damage. Melamine [13] and other substances which can contribute to ill health effects [14] can be easily determined in milk with SERS.
Want to learn more about Melamine and how to measure it with SERS? Check out this free Application Note for further information.
Trace Detection of Melamine in Dairy Products with MISA
Download our free Application Note below to learn about the rapid detection of the alkaloid trigonelline in coffee, which reduces in concentration the darker the beans are roasted.
Fast and Selective Detection of Trigonelline Coffee Quality Marker
The ripeness of fruits and vegetables is not just important information when planning meals, but it is also critical for food transport. Perishable fruits and vegetables are often shipped in an unripened state so they arrive at their destination in top condition. Freshness in citrus fruits can be determined with portable Raman instruments by measuring the carotenoid content [15].
Aside from the freshness, it is also possible to detect if pesticides, fungicides, herbicides or other harmful substances have been sprayed onto fruits using SERS [16].
Check out our selection of free Application Notes below about the determination of these kinds of substances on different fruits with MISA.
Trace Detection of Thiram on Apples
Conclusion
Several food quality parameters can be measured quickly and easily with Raman spectroscopy without the need to open bottles or destroy samples. Portable and handheld instruments make measurements simple to perform nearly anywhere.
Your knowledge take-aways
Learn more about rapid food analysis with Raman spectroscopy
References
[1] Dranca, F.; Oroian, M. Kinetic Improvement of Bioactive Compounds Extraction from Red Grape (Vitis vinifera Moldova) Pomace by Ultrasonic Treatment. Foods 2019, 8, 353. doi:10.3390/foods8080353
[2] Pan, C.; Zhu, B.; Yu, C. A Dual Immunological Raman-Enabled Crosschecking Test (DIRECT) for Detection of Bacteria in Low Moisture Food. Biosensors 2020, 10, 200. doi:10.3390/bios10120200
[3] Trebolazabala, J.; Maguregui, M.; Morillas, H.; et al. Portable Raman spectroscopy for an in-situ monitoring the ripening of tomato (Solanum lycopersicum) fruits. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2017, 180, 138–143. doi:10.1016/j.saa.2017.03.024
[4] Lin, S.; Hasi, W.-L.-J.; Lin, X.; et al. Rapid and sensitive SERS method for determination of Rhodamine B in chili powder with paper-based substrates. Analytical Methods 2015, 7, 5289–5294. doi:10.1039/c5ay00028a
[5] Li Vigni, M.; Durante, C.; Michelini, S.; et al. Preliminary Assessment of Parmigiano Reggiano Authenticity by Handheld Raman Spectroscopy. Foods 2020, 9(11), 1563. doi:10.3390/foods9111563
[6] Logan, B.; Hopkins, D.; Schmidtke, L.; et al. Authenticating common Australian beef production systems using Raman spectroscopy. Food Control 2021, 121, 107652. doi:10.1016/j.foodcont.2020.107652
[7] Santos, C; Zhao, J.; Dong, X.; et al. Predicting aged pork quality using a portable Raman device. Meat Science 2018, 145, 79–85. doi:10.1016/j.meatsci.2018.05.021
[8] Liu, Z.; Yu, S.; Xu, S.; et al. Ultrasensitive Detection of Capsaicin in Oil for Fast Identification of Illegal Cooking Oil by SERRS. ACS Omega 2017, 2, 8401–8406. doi:10.1021/acsomega.7b01457
[9] Alvarenga, B.; Xavier, F.; Soares, F.; et al. Thermal Stability Assessment of Vegetable Oils by Raman Spectroscopy and Chemometrics. Food Analytical Methods 2018, 11, 1969–1976. doi:10.1007/s12161-018-1160-y
[10] Yao, C.; Cheng, F.; Wang, C.; et al. Separation, identification and fast determination of organophosphate pesticide methidathion in tea leaves by thin layer chromatography–surface-enhanced Raman scattering. Analytical Methods 2013, 5, 5560. doi:10.1039/c3ay41152d
[11] Li, S.; Shan, Y.; Zhu, X.; et al. Detection of honey adulteration by high fructose corn syrup and maltose syrup using Raman spectroscopy. Journal of Food Composition and Analysis 2012, 28, 69–74. doi:10.1016/j.jfca.2012.07.006
[12] Oroian, M.; Ropciuc, S. Botanical authentication of honeys based on Raman spectra. Journal of Food Measurement and Characterization 2017, 12, 545–554. doi:10.1007/s11694-017-9666-3
[13] Nieuwoudt, M.; Holroyd, S.; McGoverin, C.; et al. Rapid, sensitive, and reproducible screening of liquid milk for adulterants using a portable Raman spectrometer and a simple, optimized sample well. Journal of Dairy Science 2016, 99, 7821–7831. doi:10.3168/jds.2016-11100
[14] Lin, X.; Hasi, W.-L.-J.; Lou, X.-T.; et al. Rapid and simple detection of sodium thiocyanate in milk using surface-enhanced Raman spectroscopy based on silver aggregates. Journal of Raman Spectroscopy 2014, 45, 162–167. doi:10.1002/jrs.4436
[15] Nekvapil, F.; Brezestean, I.; Barchewitz, D.; et al. Citrus fruits freshness assessment using Raman spectroscopy. Food Chemistry 2018, 242, 560–567. doi:10.1016/j.foodchem.2017.09.105
[16] Xie, J.; Li, L.; Khan, I.; et al. Flexible paper-based SERS substrate strategy for rapid detection of methyl parathion on the surface of fruit. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2020, 231, 118104. doi:10.1016/j.saa.2020.118104
