Food adulteration has been around since the Victorian times when cheese was often coloured with lead salts, beer and milk were watered down and flour was bulked out with chalk dust or ground bones .
Governments apply stringent legislation and quality standards to food products but the practice of adulteration, driven by greed and profit, is still seen.
FTIR spectroscopy is a suitable method for the characterization of food samples, detecting pollutants, measuring nutrients and even detecting fraudulent contents.
There have been some very notable cases of food adulteration that highlight a problem rife in world markets . In November 2015 the Times of India  reported that Indian police had discovered spices were being adulterated with potentially toxic chemicals such as varnish, paint and glue to make them more attractive before selling them to the public. With the Indian spice market worth almost US $2.5 billion a year  adulteration is a serious problem for both business and public confidence.
The Chinese milk scandal in 2008  resulted in the melamine poisoning of 300,000 babies across China. In this case the Chinese company responsible was prosecuted and two of their executives were executed for the crime.
The horse meat scandal in 2013  showed that Europe is not immune to food adulteration and the reputation of many well-known food companies was questioned. This resulted in the public throwing away 18 million ready meals; public confidence in the food supply hit an all-time low and the ready meal market collapsed .
Companies have found out the hard way that the integrity and provenance of the supply chain is directly linked to their business reputation and they have a legal and public obligation to make sure their products are safe and genuine.
Fourier transform infrared (FTIR) spectroscopy is an attractive technology for the food industry for testing the authenticity of produce; it is simple, rapid and provides non-destructive measurements . The Specac Pearl FTIR transmission spectrometer accessory and Quest ATR spectrometer accessory are two great options for this analysis.
The globalized import and export of produce means there is a new focus on the safety and provenance of raw materials before they enter manufacturing. FTIR has long been used to supplement quality and process control in the food industry. It is the perfect way to detect food adulteration. A high degree of accuracy, multivariate data analysis methods and its ease of operation make FTIR an ideal method for rapidly screening large volumes of produce whilst characterizing food components down to concentrations as low as parts per billion.
The four most adulterated foods
Four of the most commonly adulterated foods are alcohol (such as wine and spirits), olive oil, powdered milk and meat products.
It is not unknown for alcohol to be laced with industrial chemicals such as methanol or ethylene glycol which, if ingested, can lead to blindness or death. Olive oil contamination is a constant battle for the authorities in Spain and Italy, as extra virgin olive oil is a high value item the illegal adulteration with cheaper oils is a common occurrence. Milk powder is a common ingredient in food manufacturing and has to undergo stringent checks for moisture, fat and protein content to be sold at the highest prices.
There have been cases where melamine or other industrial chemicals have been added to increase the nitrogen content and try and fool tests for the quantitative analysis of protein. The water content of meat is a constant battle for food authorities and the amount allowed for flavouring or texture enhancement has strict limits.
Alcohol adulteration is a global problem but is of particular concern in India and the Far East as alcoholic drinks are so expensive.
Spirits and wine, particularly budget varieties, have been found to contain industrial dyes, toxic alcohols and even chemicals such as ammonium nitrate  and this kills over 100 people every year . A study in India in 2006  showed that 64% of alcoholic beverage samples tested had toxic methanol content and very few had no methanol at all. Ingesting only 30 mLl of methanol can cause death .
The use of near infra-red (NIR) spectroscopy with attenuated total reflectance is a reliable way to analyse alcohol for adulteration. NIR and ATR are used to overcome the problems of strong absorbance in the mid IR region where the IR chemical fingerprint signals for contaminants are detected. Other NIR methods have used multivariate analysis and chemo-metrics to enhance the mid IR region signals and provide greater accuracy  .
The Pearl™, a liquid transmission accessory for FTIR produced by Specac, can be used to determine the presence of any adulteration in liquid alcohol samples. The Pearls’ injection port means a definitive analysis can be carried out even if the spirit in question contains highly volatile components.
Extra virgin Olive oil is a high value flagship product in European countries such as Spain, Italy and Greece and production volumes are low. To maximise profits, some suppliers have been known to adulterate their olive oil with cheaper alternatives such as palm, peanut or even industrial oil.
In 2013 the Workshop on Olive Oil Authentication in Madrid released figures that showed one in four olive oils sampled in Spain, and nearly one in three in Canada, failed official fraud tests . The contamination of extra virgin olive oil for profits is rife and has led to a demand for more stringent testing . A research project on olive oil authentication has been included in the European Union’s Horizon 2020 research program.
FTIR is an excellent analysis method for oils particularly when used with ATR. It only requires minimal sample preparation and is able to detect and quantify adulterants by identifying ‘tell-tale’ functional groups using a fingerprint technique.
In a 2015 study examining the adulteration of extra virgin olive oil with peanut oil  an FTIR method with an attenuated total reflectance sampling technique and multivariate analysis, was developed. The study examined two sets of frequencies to establish a robust regression model, which were from 600 to 1,800 cm−1 in the fingerprint region and from 2,750 to 3,050 cm−1 in the functional group region. A method was developed that could detect contaminant oils at a level of 0.5% v/v and the FTIR spectra obtained confirmed that every oil has a unique fingerprint.
The Pearl™ can be used to establish the authenticity of olive oil samples in their native state. The Pearl’s’ high accuracy means the chemical fingerprint of low-grade oils can be detected even at low concentrations and its design means even the most viscous of oils are removed easily following measurement; which prevents error in future experiments.
Milk powder is a major ingredient in food manufacturing and as a commodity can come from various sources. There have been a number of cases in Brazil, India and China concerning adulteration of powdered milk using chemicals such as urea or melamine to increase nitrogen content and in some countries, for example India , the practice is common. In 2012 the Food Safety Standards Authority of India (FSSAI) found that 70% of milk samples from across the country were contaminated .
FTIR is routinely used by food companies to determine moisture, fat, protein and lactose content for QA/QC and in-line process control and its use has now been extended to detect dangerous contamination . A study in 2011  showed how FTIR spectra collected in the mid infrared (MIR) region between 4000 and 600 cm−1 could be used to detect melamine contamination. FTIR data was processed using regression and multivariate analysis and spectral changes in the amide I and II regions (1700–1400 cm−1) and the fingerprint region (1800–700 cm−1) were used to identify and quantify contamination and provide a model for future analysis.
Powdered milk samples can be accurately analysed for any contamination using the Quest™ ATR accessory. As there is no need for sample preparation the Quest™ facilitates high throughput quality control.
Adding water to meat is a controversial subject and EU regulations actually allow a significant amount of water to be added. Chicken can contain 7% added water and ham up to 25% but often they contain much more. Canned and prepared meats routinely contain lots of hydrolysed protein, polyphosphates, salt, lactose or dextrose and these all retain water.  Some prepared meats are only around 54% meat the rest being water, gelatine and starch.
In 2000 the FSA found that one third of supermarket chickens tested had much more than the 7% water limit allowed and in some cases this was up to 37%.
A qualitative model for discriminating water-injected meat, gum-injected meat from normal meat was developed in 2014 by a Chinese research group . Using near infrared spectroscopy (NIR), principal component analysis (PCA) and discriminant analysis the accuracy in distinguishing between normal and adulterated meat was 94.23% when the amount of water injection was 1.25%–20%, and this was increased to 96.96% upon water injection at levels between 3.75% and 20%.
The Quest™ can also be used to measure completely solid samples, such as a cut of meat. This characteristic wavelengths of water (or any other adulterants) to be observed and quantified with no damage done to the product itself. This form of non-destructive testing is highly suitable for food quality control purposes.
The Pearl™ is a liquid transmission accessory, designed by Specac to handle FTIR sample analysis in the near and mid Infrared range. This system enhancement is able to significantly reduce the time and difficulty of liquid sample analysis.
The Oyster™ cell also has an injection port allowing volatile samples to be examined. The Pearl™ was designed to provide a much more accurate path length than traditional liquid transmission accessories, with pathlengths repeatable to within 1 µm.
The Pearl™ can also be fitted with ZnSe or CaF2windows, which can be interchanged in seconds and the Oyster™ cells are available in path lengths of 50µm, 100µm, 200µm, 500µm and 1000µm.
The specific benefits of the Pearl™ include:
- ease of FTIR sampling
- faster and more reliable than traditional liquid cells
- accurate and repeatable pathlengths
- available as parallel or wedged cells to eliminate fringing
- handles viscous materials such as oils with ease
The Pearls’ highly accurate liquid transmission capabilities, alongside a conventional ATR IR spectrometer, can be used to identify almost any form of food adulteration regardless of if the sample is an aqueous solution, an oil, a powder or a solid. It’s ease of use means, alongside FT-IR processing software, a low level of skill is required to use the instrument, allowing its integration easy integration into food processing environments.
Original article link:
- Atkins, P.J. (2011), ‘The Material Histories of Food Quality and Composition’, Endeavour, 35: 74‒9.
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