Spectroscopic Techniques for Food Analysis to Combat Adulteration and Fraud

Consumers in developed countries rarely think about the authenticity of their food and drink. Perhaps they should, as the threat from fake foods is real and the potential health ramifications dire.

Food fraud takes many forms, including adulteration, package tampering, outright counterfeiting of products or ingredients, mislabeling, intentional use of illegal or substandard ingredients, manufacturing shortcuts to lower production costs, and many others.

Quantifying the financial impact of food fraud is difficult. The oft-repeated figure is $49 billion (US) per year, as proclaimed by NSF International, the U.S.-based Grocery Manufacturer’s Organization, venerable organizations like Battelle and the U.S. Food and Drug Administration, and many others. Unfortunately, these claims reference and lead to each other, not any original study, and online searching failed to turn anything close to this number from primary research. 

The likelihood a food will be fake depends on incentives and opportunity, tempered by market forces. Fakes of high-value items are the most lucrative, but “high-value” means something different in Europe than in south Asia. Product volume plays into the equation, as does ease of carrying out the fraud (think tap water for “spring” water). Moreover, trade agreements create legalistic opportunities, for example declaring Syrian olive oil as “Italian” if the ship carrying it passes through the Strait of Messina.

A good deal of food fraud also involves the use of bogus or substandard, but otherwise legal ingredients, the use of pesticides to boost yields of “organic” produce, or production shortcuts resulting in contamination with insect debris or metal shavings.

Thanks to modern technology, detecting food fraud is mostly an analytical chemistry exercise, with choice of methodology depending on the quality attribute the food detective is looking for. For example fat content as a proxy for butter quality, microbe titer for the viability of probiotics in yogurt, mineral content of boutique waters, or nutrient composition. 

Look but Don’t Touch – Non Destructive Testing

High-value aged meats are a food market where the need for rapid, non-destructive analysis tools are obvious. TellSpec (Toronto, Ontario) has developed a handheld near-infrared (NIR) instrument that differentiates beef cuts based on aging. 

In one study, conducted with two Hungarian research groups, TellSpec scientists demonstrated a handheld near-infrared (NIR) instrument for authenticating the extent of aging in sirloin and tenderloin samples.

NIR spectrometers measure light that is emitted, absorbed, or scattered by food samples. “Allowing us to identify and quantify the chemical composition of foods,” says TellSpec CEO Isabel Hoffman. “Analysis occurs not by the sensor but within an analytic cloud platform that connects our sensors and others to a patented food analysis engine.” Results appear on a handheld device through a mobile app.

Hoffman, recently presented a Ted Talk on detecting food adulteration using portable spectroscopic sensors. She talks of an “internet of things” approach whereby relatively inexpensive detectors transfer data to powerful remote computers, which make the analytic determinations and communicate them back to decision-makers. The company’s 136-gram handheld Enterprise Food Scanner is based on DLP(r) technology from Texas Instruments, which “interrogates” food samples with light in the NIR 900-1700 nm range, providing a readout in ten seconds. DLP is the basis of many “smart” home applications.

NIR is particularly suited to the characterization of foods, and several small form-factor point-of-use instruments are on the market. One, from the Israeli company Scio, uses a narrower spectral range, 700nm to 1000nm, than TellSpec’s. Other companies with handheld NIR devices include Pasco, BwTech, ASD.

Types of Spectroscopic Techniques for Food Analysis

Spectroscopy is a useful analytical platform for food screening because it is rapid, mobile, and nondestructive. 

Absorbance Spectroscopy 

This technique investigates a food’s chemical composition directly via wavelengths absorbed when light passes through it. Absorbance is most often used for liquids. Methods for confirming the quality of spices, for example, employ absorbance measurements. 

Absorbance can also be effective in detecting adulterated wine and spirits. Certain wines produce specific UV-Visible spectral absorbance profiles that can be used as the basis for a screening device for fast, field-based testing. Data can be compiled into libraries and help speed the testing process.

Reflectance 

Like absorbance, reflectance is a nondestructive method and yields the most information from food samples when near-infrared (NIR) and visible reflectance are over the 400-2500 nm wavelength range. Two instruments from Ocean Optics, the Flame-S-VIS-NIR and NIRQuest512-2.5, cover this region of the spectrum. Another device, the Flame-NIR, covers 950 to 1650 nm.

For spices, reflection spectroscopy can be used to identify fillers and adulterants such as less expensive spices and dyes, which are used to mask ageing. Even sawdust has been used as an adulterant, and although it’s virtually impossible to detect visually, spectroscopic analysis reveals the higher water content of sawdust compared with the spice. 

NIR

Near-infrared spectroscopy is particularly suited to nondestructive analysis of high-moisture foods, for example fruit, fish, meat and grains. NIR radiation penetrates deeply, with less scattering, than other types of spectroscopy, which creates opportunities to probe a food’s surface as well as to some depth. Due to spectral complexity, IR and NIR analyses are often followed by chemometric analysis.

Fluorescence Spectroscopy

Fluorescence spectroscopy utilizes native fluorophores in foods, yielding a wealth of information on ingredients, geographic origin, degree of aging in cheese, egg freshness, toxins in nuts and grains, and quantification of nutrients and gristle in meats. 

Surface-Enhanced Raman Spectroscopy (SERS)

Used to detect trace levels of contaminants in foods, SERS can also detect banned or substitute substances, such as banned antifungal or coloring agents, bacterial pathogens, and restricted antibiotics.

Spectroscopy has applications both in rapid screening and lab analysis, with the potential for integration into process lines. However, its greatest potential involves rapid onsite analysis, with government inspectors an obvious market. “Spectroscopic testing even could evolve to the point where it’s affordable and simple enough for consumers to use,” says Marco Snickers, who heads business development at Ocean Optics (Dunedin, Florida).

The application of chemometrics, which extracts information from very large data sets, is a relatively recent development aiding the application of spectroscopy for the detection of food fraud, particularly with large incoming data streams from multiple screening or analytical systems.

Most spectroscopy methods are today available in portable or handheld formats, says Marco Snikkers, Business Development at Ocean Optics, “in keeping with larger technology trends pushing devices that are smaller, faster, and more user-friendlly, especially as microprocessing power, instrument connectivity and power management have all advanced.”

Technique selection depends on what the user is trying to achieve. Often two or more methods used together, provide confirmation of authenticity or the presence of a contaminant. 

For example, some researchers have applied fluorescence analysis to honey, whose constituents and adulterants have identifiable fluorescence responses. In complementary fashion NIR absorbance and reflection can detect honey’s water content.

Ocean Optics (Largo, Florida, USA) offers two large-format posters, free of charge, that describe spectroscopy applications in food science.

Battle of the Analysis Methods

Food scientists rely on any and all available analytical platforms to detect fraud. Some are more definitive than others.

Extra virgin olive oil has been a product of concern due to its premium price. Authentication methods range from simple spectroscopic analyses to GC-MS, to the most elegant stable isotope quantitation methods by MS.

Sciex (Framingham, Massachusetts, USA) has described an LC-MS method which, when subjected to appropriate statistical tools, generated a principal components analysis (PCA) which they applied toward detecting adulteration of extra virgin olive oil.

Investigators created blends of authentic extra virgin oil with seed oils in various ratios, and diluted the blends with organic solvents for LC-MS analysis alongside the individual component oils and processed olive oils. Food oils share many fats and natural flavors, but principal component analysis showed groups of compounds in each of the oils that were absent in the other oils. Phil Taylor, Global Marketing Manager for Food, Environmental, and Forensics, refers to these compounds as “unique identifiers.” 

The same approach has been used to identify horse meat in processed food products where it should not be present, a method for which Sciex has presented data and a method. 

PCR has also been used to detect contamination in meat, including the presence of enteric bacteria and non-advertised species (e.g. pork in “beef” meatballs). PCR is rapid, sensitive, and specific, but MS is more versatile.

“With PCR you can only look at one species at a time,” Taylor notes. “LC-MS can detect multiple analytes and species.” For example the same LC/MS platform can detect chemical patters indicative of horse meat in beef as well as pesticide and drug exposure or any number of other quality attributes in another without any downtime to your productivity. Where a typical LC/MS analysis runs in less than 30 minutes, PCR temperature cycling can go on for hours, involves more detailed sample preparation, suffers from cross-reactivity, and processing may destroy the “evidence.”

“LC/MS is just more versatile and less susceptible to extraneous factors related to the analysis or how the food product was processed,” Taylor says.

Additionally, a collaboration between PerkinElmer (Waltham, MA) and researchers from North Texas University has resulted in a method for authenticating virgin olive oil by its thermal properties using differential scanning calorimetry (DSC). DSC is used commonly in food science labs as a quality control test. 

Investigators found that commercial olive oils show distinct thermal properties during cooling, with pomace and extra virgin showing the most distinct differences. To test whether these differences could distinguish pure extra virgin oil from product cut with pomace oil, they created blends and tested their thermal properties. Investigators found that the addition of 7% or more of pomace to extra virgin was detectable, and on this basis concluded that the supermarket brand was adulterated with up to 15% of the lower-grade product.

Conclusion

Food fraud may occur at any point in the value chain. “We receive inquiries not just from big producers but from manufacturers of ingredients, and even retailers, but most requests come from the middle of the supply chain. Adulteration or fraud can even occur during transportation,” according to Rob Packer, Ph.D., Infrared Portfolio Director at PerkinElmer.

In PerkinElmer’s experience, fraud occurs mostly in high-value products (spices, honey, oil) or in mass-produced foods whose standard authenticity tests are easily defeated by clever formulators. Examples include melamine-laced milk powder and dog food, which surfaced in U.S. markets in 2007 and 2009, respectively. A standard quality measure of those products is protein content, for which “total nitrogen” serves as a proxy. Melamine, a poison, contains lots of nitrogen.

No authentication test is 100% invulnerable. To combat fraudsters, stakeholders must develop new tests and novel combinations thereof, presenting counterfeiters with the nearly impossible task of guessing which tests will be applied.

This raises the question of screening vs laboratory testing? As testing every food production lot at various steps along the supply chain is out of the question, the availability of rapid, accurate screens (followed by confirmatory tests if needed) is essential.

In those instances, notes Packer’s colleague, General Manager for Mass Spectrometry Kaveh Kahen, Ph.D., mass spectrometry has become the go-to confirmatory method. “Mass spec generates a distinct molecular signature in olive oil. It can analyze for low-level adulterants as well as macro ingredients, and can even establish the origin of food products.”