2. NEAR-INFRARED SPECTROSCOPY
Measurements in the near-IR (NIR) spectral region (0.7–2.5 μm,
equal to 700–2500 nm) are more widely used for quantitative
analysis. Several commercial instruments are available for
compositional analysis of foods using NIR spectroscopy. A major
advantage of NIR spectroscopy is its ability to measure directly the
composition of solid food products by use of diffuse reflection
techniques.
3. NEAR-INFRARED SPECTROSCOPY
NIR absorption spectra are less useful for identification and more useful for
quantitative analysis of compounds containing functional groups made up of
hydrogen bonded to carbon, nitrogen, and oxygen.
NIR spectroscopy is used most extensively for quantitative applications, using
either transmission or diffuser flection measurements that can be taken directly
from solid foods. By using multivariate statistical techniques.
NIR instruments can be calibrated to measure the amounts of various constituents
in a food sample based on the amount of IR radiation absorbed at specific
wavelengths.
4.
5. PRINCIPLES
When radiation strikes a solid or granular material, part of the
radiation is reflected from the sample surface. This mirror-like
reflection is called specular reflection, and gives little useful
information aboutthe sample.
Most of the specularly reflected radiation is directed back toward
the energy source. Another portion of the radiation will penetrate
through the surface of the sample and be reflected off several
sample particles before it exits the sample.
6. PRINCIPLES
This is referred to as diffuse reflection, and this diffusely reflected radiation
emerges from the surface at random angles through 180◦. Each time the
radiation interacts with a sample particle, the chemical constituents in the
sample can absorb a portion of the radiation. Therefore, the diffusely reflected
radiation contains information about the chemical composition of the sample, as
indicated by the amount of energy absorbed at specific wavelengths.
The amount of radiation penetrating and leaving the sample surface is affected
by the size and shape of the sample particles. Compensation for this effect may
be achieved by grinding solid or granular materials with a sample preparation
mill to a fine, uniform particle size, or by applying mathematical corrections
when the instrument is calibrated
7. How Does Near Infrared Spectroscopy Work?
NIR works because specific organic molecules absorb specific
wavelengths of NIR (near infrared) light energy. The absorptions are
directly correlated with the concentration of the organic molecules.
This relationship must be scaled by a primary technique, otherwise
known as the wet chemistry laboratory. Therefore, the NIR is
dependant upon the wet chemistry methods to attain the linear
relationship between the molecular absorptions and the actual
constituent concentrations.
9. NEAR INFRARED SPECTROSCOPY
Near infrared spectroscopy is routinely deployed in food, agricultural, dairy,
pharmaceutical, chemical, petrochemical and feed industries. The application of the
technology varies in each industry, and many applications are custom designed to suit
different companies and their specific products and needs. NIR spectroscopy has been
successfully used in the production of cheese, meat and meat products, fish, egg
products, milk, butter, beer, wine, fruit juices, baked goods, cereal, produce, jams,
jellies, nutritional supplements and more. Some of the common applications include
measuring:
-Fat levels -Sugar content
-Moisture content -Blend uniformity analysis
-Starch content -Protein
-Oil content
10. NEAR INFRARED SPECTROSCOPY
-To evaluate composition and quality of red meats and processed meat
products poultry and fish.
-measuring specific chemical constituents in a food that affect its end-use quality, -
-for monitoring changes that occur during processing or storage, and for directly
predicting processing characteristics of a commodity that are related to its
chemical composition
11. NEAR INFRARED SPECTROSCOPY
-Incoming raw materials can be analysed by NIR to verify
that suppliers are sending a quality material.
-The product mix (dough, etc.) can be analysed by NIR to ensure that
all ingredients were added correctly.
12. NEAR INFRARED SPECTROSCOPY
-Finished product can be analysed by NIR to ensure product quality
and to verify label claims.
-Raw fruit can be analysed by NIR to determine optimum oil and
moisture content before harvest
-Expenditure and dependence on expensive Wet Chemical analysis
can be significantly reduced
-Real time results can be achieved for industries requiring fast
process analysis
13. NEAR INFRARED SPECTROSCOPY
-Determination of property concentrations
-Identification of raw materials in intermediate and finished products
(qualitative analysis)
-Specific properties concentrations (quantitative analysis) can be
analysed based on their importance in the process (for example):
◦ Moisture control (important because it affects the taste of the
product and has microbiological impacts on shelf life)
◦ Fat or oil (affects the taste of the product)
◦ Control of fat added to product, in the form of spray oil, etc., (an
important cost savings for food plants).
14. NEAR INFRARED SPECTROSCOPY
ADVANTAGES
NIR spectroscopy is a proven and accepted method of food
analysis and is used to monitor product quality parameters
within the food, beverage, and dairy industries and offers
significant advantages:
-Real-time analysis
-Measure multiple constituents simultaneously
-Non-destructive testing
-No chemical waste stream, environmentally friendly
-Less sample waste
-Decrease operation costs, increase yield!
15. NEAR INFRARED SPECTROSCOPY
DISADVANTAGES
-Must still measure reduced set of samples with wet chemistry
-Calibration is less accurate than wet chemistry
-Measurement outside of range of calibration samples is invalid
-Small calibration sample sizes can lead to over confidence
16.
17.
18.
19.
20. Absorption Bands in the NIR
Region
The absorption bands observed in the NIR region are
primarily overtones and combinations.
The bonds involved are usually C—H, N—H, and O—H.
The amount of radiation penetrating and leaving
the sample surface is affected by the size and shape
of the sample particles. Compensation for this effect
may be achieved by grinding solid or granular materials
with a sample preparation mill to a fine, uniform
particle size, or by applying mathematical corrections
when the instrument is calibrated
21. NIR region arise primarily from functional groups that have a hydrogen atom attached to a carbon, nitrogen ,or
oxygen, which are common groups in the major constituents of food such as water, proteins, lipids, and
carbohydrates.
Note that strong absorption bands associated with the −OH groups of water are centered at ca. 1450 and 1940 nm.
These bands are the dominant features in the spectrum of cheese, which contains 30–40% moisture, and they are
still prominent even in the lower moisture wheat and egg white samples. Bands arising from the −NH groups in
protein.
