What is NIR and how is it used in Food Testing
Introduction to NIR Measurement
Near Infrared, or NIR, spectroscopy is an analysis technique for fast, accurate food testing. NIR measurement is a widely-used method in the food and drink and agricultural industries, and it is a convenient, low cost alternative to chemical analysis.
This introduction to NIR measurement explains how NIR works, what it measures, and why it is a rigorous, effective means of food testing.
Essential Quality Control for Foodstuffs
Food quality is a critical issue in the food and drink and agricultural sectors, and food contamination is a continuing issue, with meat and alcohol being two of the most frequently adulterated items.
Food suppliers, retailers and their customers all need to have complete confidence in the food that is readily available, on a domestic and global scale.
NIR measurement is highly effective in the quality control of a broad range of foodstuffs and supports various aspects of food processing, including:
· Identifying ingredients and additives
· Composition analysis for food labelling
· Detecting food fraud
· Optimising manufacturing and production processes.
What is Infrared Energy?
Infrared energy is electromagnetic energy from molecular vibration. It is radiant and invisible to the human eye.
All objects emit some level of infrared (IR) radiation. When atoms absorb the release energy, these produce the frequencies that release energy as IR.
The electromagnetic infrared spectrum is similar to the visible light spectrum, in that it has a range of wavelengths, from shorter, near infrared waves to longer, far infrared waves.
Near infrared (NIR) waves are closer to visible light on this spectrum and do not emit detectable heat.
Infrared Sensing Applications
The IR spectrum is a highly effective application in sensing and detection. Typical applications include electronic sensors in infrared cameras and night-vision goggles.
Infrared spectroscopy measures infrared emissions from materials using specific wavelengths. A substance will have its IR bandwidth, which shows peaks and dips where electrons in molecules emit or absorb light photons.
NIR represents a particular region of the electromagnetic spectrum, and in NIR measurement, various instruments can analyse materials using infrared light.
How NIR Measurement Works
The NIR region of the electromagnetic spectrum is about 700 to 2500 nanometers.
NIR spectroscopy measures light that is scattered off and through sample material, and this can rapidly determine the material’s properties.
This process has no effect on the material itself.
NIR measurement then converts this information into data which forms the basis for further action, whether this is in the field of research, quality control or production.
This form of analysis requires little or no preparation of samples, and it can measure multiple parts in a single scan. It can also examine irregular surfaces.
NIR is therefore ideal as a method for analysing different foodstuffs.
What Can NIR Measure?
The most common uses of NIR spectroscopy in the food and drink and agricultural industries are for measuring food content such as protein, carbohydrate, moisture, fat, food oils and different polymers.
In food production, ingredients, additives and stabilisers are commonplace for colouring, flavouring, thickening and blending purposes.
Raw materials such as grains naturally have various properties.
As a quality assurance and control method, NIR can measure organic, pure substances, as well as some inorganic minerals and salts.
These substances include:
· Vitamins and nutrients
· Amino Acids
· Fats and fat replacers
· Stabilisers, binders and thickeners
· Sweeteners and sugar replacements.
What NIR Measurement Tells Us About Food
These various substances in food give off unique infrared emissions. Therefore, NIR measurement can tell us what proportion of these substances there is in a specific food compound.
It is about the balance of these elements. For example, it can show the proportion of moisture or fat.
The concentration of these elements is expressed through the various levels of intensity of specific infrared colours.
But what causes these compounds to display different IR colours?
Different NIR Processes
There are two processes in NIR measurement, reflectance and transmission. Which process you use depends on the foodstuff you wish to analyse.
Different compounds display different IR colours because certain molecular bonds absorb distinct infrared light wavelengths.
The reflectance process involves reflecting light from the sample, measuring its absorbent qualities by how much light is reflected back.
With transmission, the infrared light passes through the sample, measuring how much light the sample absorbs.
Depending on the type of foodstuff, one process or the other will be better suited to NIR measurement.
For example, transmission works well with wholefoods, such as inspecting food for its ripeness, or whether it contains pests or defects.
It is also useful for measuring fat and protein content in various dairy products; and for measuring wine quality, including tannin content.
Reflectance is good for measuring content in wholegrains such as protein, moisture and oil content.
It can be a challenge to interpret and analyse bulk items of food, while ensuring that these processes do not affect the subject material in any way.
NIR measurement is the perfect solution to bulk analysis of items such as grains, fruit, meat and fish.
NIR light can penetrate deeply to analyse internal composition.
It is also especially valuable in gluten screening when sorting unprocessed grains.
The Importance of Calibration
An NIR measurement device must first know the parameters of the substance it is measuring.
For accuracy, this means calibrating the device through a comparison of its initial IR data with reference analysis data.
This comparison is in the form of mathematical equation.
This is how the process works: the device takes a first infrared absorption reading of a substance or material it has not measured previously. This is the basis of the equation on which the device will then calibrate itself for subsequent readings.
It stores this calibration in its memory.
Instruments for NIR measurement will have pre-set factory calibrations, but there are several calibration techniques which you can then apply to produce the necessary algorithm for a specific calibration.
These techniques include basic multi-linear regression (MLR) and the more advanced partial least squares (PLS).
The calibration model you use will depend largely on the food compound you wish to analyse and the type of instrument you are using.
All analytical methods have a certain degree of variability, and NIR generally has an accuracy of 1.5 times the variability of the reference method it bases itself on.
Modern NIR measurement technology uses highly accurate prediction equations, based on vast databases, which draw on comprehensive NIR to wet-chemistry comparisons.
For analysis and testing of multiple samples quickly, NIR is an efficient, accurate method.
Bringing the Lab to the Sample
NIR measuring devices are continually evolving, becoming increasingly versatile and portable.
There is a new generation of handheld analysers which are making NIR measurement that much more convenient.
These include highly accurate devices such as the Spectrolytic Oil Seed Analyser.
Modern, cutting edge NIR instruments allow for the swift, large-scale analysis of both liquid and solid food samples.
They play an essential part in food analysis and testing throughout the supply chain, from raw materials to intermediate and finished food and drink products.
For a broad variety of food producers and industry professionals, NIR measurement offers these principal benefits:
· It cuts down significantly on waste, with no sample preparation required
· There are no errors associated with traditional lab-testing methods
· It is suitable for a wide range of solid and liquid compounds
· NIR provides a highly effective, speedy solution to analysing multiple components
· Instruments are extremely user-friendly, and do not require any special skills.