From The Editor | October 3, 2023

NIRS: A Quick And Easy Way To Detect Allergens

John Oncea

By John Oncea, Editor

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A University of Illinois study used near-infrared spectroscopy to detect allergens in quinoa flour. The method is highly accurate and researchers say it will not be difficult to develop low-cost miniature sensors based on their methodology.

Food allergies affect about 2 percent of adults and 4 to 8 percent of children in the United States, according to the U.S. Department of Agriculture. Many of these occurrences lead to anaphylaxis* resulting in an estimated 30,000 emergency room visits, 2,000 hospitalizations, and 150 deaths per year. Even small traces of allergens can cause severe reactions and the food production process can easily cause cross-contamination meaning dependable allergen testing methods are crucial.

According to Food Safety Magazine, the most common method for food allergen analysis is immunoassays, which use antibodies that recognize proteins from the food allergen material. These methods include enzyme-linked immunosorbent assay (ELISA) testing, lateral flow devices, and real-time PCR.

Now, a University of Illinois (Go, Fighting Illini!) study has found the application of near-infrared (NIRS) spectroscopy was able to detect three types of allergens in quinoa flour. The researchers say the method is fast, easy, non-invasive, inexpensive, and highly accurate and “could benefit millions of people around the world who suffer from food allergies.”

* Anaphylaxis is a severe, life-threatening allergic reaction, according to the Mayo Clinic. It can happen seconds or minutes after you’ve been exposed to something you’re allergic to with peanuts and bee stings being two common examples. “In anaphylaxis, the immune system releases a flood of chemicals that can cause the body to go into shock. Blood pressure drops suddenly, and the airways narrow, blocking your breathing. The pulse may be fast and weak, and you may have a skin rash. You may also get nauseous and vomit. Anaphylaxis needs to be treated right away with an injection of epinephrine. If it isn’t treated right away, it can be deadly.”

A Little Bit About NIRS

“Near-infrared spectroscopy or near-infrared spectrophotometry (NIRS) is an absorption spectroscopy method that helps determine the chemical composition of a compound or solution by measuring how much near-infrared radiation the compound or solution absorbs,” writes tec5USA. NIRS operates in the near-infrared electromagnetic spectrum in waves covering 700 nm to 2500nm, slightly longer than those of visible light, and is present in optical fiber and TV remotes.

NIRS, like all spectroscopy methods, adheres to the Beer-Lambert Law which states the concentration of a certain chemical compound in a solution determines how much light, whether visible or infrared, this solution will absorb: the higher the concentration, the more radiation of a specific wavelength will be absorbed.

“However, NIRS differs from other spectroscopy methods in the mechanisms behind this absorption,” tec5USA explains. “For instance, in UV-Vis spectroscopy, the absorption of visible light by a chemical compound is measured based on the absorption of electromagnetic radiation by the electrons that constitute the compound.

“When an electron absorbs the radiation, it enters the so-called excited state where it is ‘charged’ with more energy than in its normal (‘ground’) state. However, electrons don’t stay excited for a long time and decay to their ground state shortly after, releasing the equivalent amount of energy that they had absorbed. This process is also known as the electronic transition.”

On the other hand, NIRS works differently as near-infrared radiation interacts with entire molecules instead of exciting the electrons within the atoms of an element. This interaction affects the vibrational motion of the molecules, specifically, the bonds that hold the atoms together within a molecule.

When near-infrared radiation is present, a molecule will absorb the electromagnetic photons and begin a process called vibrational transition which involves stretching, shrinking, bending, and rocking back and forth. Due to this mechanism, NIRS is often referred to as vibrational absorption spectroscopy. This process observes how molecules behave during vibrational transitions to determine their chemical composition based on their specific vibrational modes.

“Let’s consider a molecule of water as an example,” tec5USA writes. “A molecule of water consists of two partially positively charged atoms of hydrogen connected to a partially negatively charged atom of oxygen. When exposed to specific frequencies of infrared radiation, the water molecule is excited to one of the following higher-energy vibrational modes:

  • Asymmetric stretch, during which one of the hydrogen bonds shrinks while the other extends
  • Symmetric stretch, during which both hydrogen bonds shrink or stretch
  • Scissoring bend, during which both hydrogen atoms rock back and forth toward each other as if they were impaled by a pair of scissors.”

Determining a molecule's vibrational mode and the frequency of infrared radiation needed to excite it is the basis of NIRS.

Using NIRS To Detect Food Allergens

U.S. regulations specify nine major food allergens: milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, sesame, and soybeans. Cross-contamination can occur during refining, manufacturing, and packaging if cleaning is neglected.

According to Optica, “The seeds of the quinoa plant — which are often referred to simply as quinoa — have been growing in popularity as a gluten-free food, high in protein and vitamins. Quinoa itself does not contain any of the major food allergens. But if allergenic grains or legumes get into the equipment that grinds quinoa into flour, consumers with allergies to those contaminants may suffer.”

Illinois researchers added sesame, peanut, and wheat flour at ratios that varied from 3% to 98% allergen contamination into ground quinoa flour to test the ability of a compact NIR-spectroscopy setup to detect contaminants. The specimen set also included samples of pure allergen flour for comparison.

“The Illinois researchers scanned the flour samples with two instruments: a benchtop Fourier-transform NIR spectrometer, which scanned the wavelength range of 867 to 2500 nm, and a filter-based NIR spectrometer that scanned at 10 predefined wavelengths between 1680 and 2336 nm,” Optica writes. “Then the team developed a partial-least-square regression model to analyze the spectral plots for multiple allergens. Additional mathematical preprocessing improved the model’s ability to distinguish among the types of flour.”

The engineers discovered that choosing nine spectral bands from the benchtop system and creating a regression model yielded more precise outcomes compared to using the full-spectrum or predefined-wavelength data. This approach has the potential to create an affordable filter-based spectroscopic tool that can detect food allergens and can be utilized in commercial kitchens, industrial settings, and even at home.

“Detecting adulterated allergenic components in food could benefit millions of people around the world who suffer from food allergies,” said Qianyi (Lisa) Wu, an undergraduate student in the Department of Agricultural and Biological Engineering, part of the College of Agricultural, Consumer and Environmental Sciences and The Grainger College of Engineering at U of l, and lead author on the paper.

“NIR spectroscopy offers numerous advantages. It is non-destructive, non-invasive, and doesn’t use chemicals. It provides results in real-time, and with a short training period, anyone can perform the analysis,” added Mohammed Kamruzzaman, assistant professor in ABE and Wu’s faculty advisor and corresponding author on the paper.

NIRS In The Real World

NIRS is a helpful tool for detecting the presence and amount of sugar and ethanol in chemical compounds, making it a common method for quality control during the production of beverages that contain these compounds, like beer. Proper proportions of alcohol, fermentable sugar, non-fermentable sugar, diacetyl, and alpha acids are crucial for the quality of the final product in beer brewing.

“All of these components are organic compounds that can be accurately measured at any point during the fermentation and brewing process using NIRS testing,” tec5USA writes, adding, “Considering how useful NIRS testing can be in beverage production, it only makes sense that it is equally useful in the quality control of food products.

“That’s because near-infrared spectroscopy is capable of identifying and measuring essential food components and nutrients, from the sugar that we mentioned to fats, proteins, carbohydrates, and more. Near-infrared light is not blocked or interrupted by translucent materials, such as glass. As a result, NIRS can be used to evaluate the quality of food products without disturbing the final packaging.”