Measuring Fat Content of Dairy Products by NMR

MethodFATLab Note 010

Sample*Stated fat
content (%)

Measured fat
content (%)

Difference – relative
to calibration line
derived from all
samples (%)

Butter

81.3

81.9

+0.6

Low fatstrawberry
yoghurt

0.8

1.1

+0.3

Labyoghurt
Note 010 5.5

5.3

-0.2

Low fatcrème fraiche

15.0

14.9

-0.1

Crème fraiche

30.0

30.5

+0.5

A variety of dairy
a rangefat contents
between
1% and 82%
filterproducts
sampleswith
wereplacedofinside
glass vials.
All samples
werewere analysed
Singlethecreamby NMR using an MQC-23 fitted with a 26mm 1H probe. Analyses were conducted using
conditioned
at 40ºCapplicationfor one hour,priorpackage.
to analysis. NMROIMR EasyCal‘Fat in Foodstuffs’software

19.1

19.4

+0.3

50.5

49.3

-1.3

A variety of dairy products with a range of fat contents
between 1% and 82% were analysed by NMR using an
MQC-23 fitted with a 26 mm hydrogen probe. Analyses wereconducted using the EasyCal ‘Fat in Foodstuffs’ application
software package.
Samples were prepared in duplicate by spreading 3–5 gasuring Fat ofContentof Dairy
Products
by NMR
each sample
on glass
fibre filter paper
and placing eithera) on a metal dish or b) directly inside a glass vial. All samples
were dried in an oven at 103°C for ~5 hours (drying time
Methoddependent on amount of sample). After drying, the open-

measurement time was ~32 seconds.

Raspberry

Double cream

Samples were prepared in duplicate by spreading 3-5g of each sample on glass fibre filter
paper and placing either a) on a metal dish or b) directly inside a glass vial. All samples were
The advantage of this method over extraction techniques is
Table
1: Fat content measured by NMR against the value *stated on thedried in an oven at 103°C for ~5 hours (drying time dependent on amount of sample).
Afterdrying, the open-filter
samples
wereofplaced
insidevials. All insamples
were conditionedthat a large
numbersamplescanglass
be preparedbatches.
packaged produce.
at 40ºC for one hour, prior to analysis. NMR measurement time was ~32 seconds.

Lab N

Results
The advantageof this method over extraction techniques is that a large number of samples
Figure 2 shows an excellent correlation was achieved using
can be prepared in batches.
Figure 1 shows that a good calibration (Correlation Coefficient

Results

four types of dairy produce and a zero control. By reducing

the calibration range (e.g. 0-20%), data from the previous= 1.00; Standard Deviation = 0.57) can be obtained using
Figure 2 shows an excellent correlation was achieved using four types of dairy produce (Figure 1 shows
good calibration(Correlation
1.00;which
Standard Deviation=
experimentgave a Correlation Coefficient of 1.00 andall that
the asamplesof dairy produce
andCoefficientan empty =tube
0%).
By reducing
the calibration range (e.g. 0-20%), data from the previous experiment g0.57) can be obtained using all the samples of dairy produce andan empty
tube which
StandardofDeviation
0.23%. Deviation of 0.23%.
represents 0%.
a Correlation Coefficient
1.00 andofStandard
represents 0%.
Figure 2

Figure 1(% Fat)(% Fat)Figure 1
Table 1Figure 2

Since the hydrogen density of the fat components will vary with food type (eg butter, milk

*StatedMeasured
Difference -oils
relativevegetable
and tomodified/blended oils) it is recommended that a calibration is generate
Samplecontent
calibration line derived
Since
the hydrogen Fat
densityof theFatfatcontent
components
will
vary
from
fat
derived(%)(%)
from all samples from(%) the same source material. Such a calibration may be generated bycalibration
method or a multi-point calibration covering the range of interest.
Butter with food type (e.g. butter,81.3 milk, vegetable
81.9 oils 100%
+0.6
and modified/
Low fat strawberry yoghurt
0.8
1.1
+0.3
blendedthat 5.3
a calibrationis generated
Raspberry
yoghurtoils) it is recommended
5.5-0.2
Conclusions
Low fat crème
15.0same source
14.9
from fraiche
fat derived from thematerial. Such a -0.1
Crème fraiche
30.0
30.5
+0.5 provides a means of rapidly measuring fat in dairy produce. Sample prepara
The MQC23
calibration may be generated
methodSingle cream
19.1 by a 100%
19.4 calibration
is simple+0.3
and conducive to very high sample throughput.
Double cream
50.5 covering 49.3
or a multi-point calibration
the range of interest.-1.3
MQC23– produce.
Enhanced Functionality
Table 1: Fat content measured by NMR against the value *stated on the
packaged

The instrument configuration used in this work may also be used to measure Oil in Dried
Snack Foods, Fat in Chocolate and other Cocoa Derivatives. The functionality of the
instrument may be increased to include the determination of Solid Fat Content (SFC), byaddition of a 1H-probe (10mm) and conditioning/tempering hardware as detailed in the
AOCS/ISO SFC protocols.

Conclusions

MQC – Enhanced Functionality

The MQC-23 provides a means of rapidly

The instrument configuration used in thismeasuring fat in dairy produce. Sample

work may also be used to measure Oil in

preparation is simple and conducive to very

Dried Snack Foods, Fat in Chocolate andhigh sample throughput.

other Cocoa Derivatives. The functionality of
the instrument may be increased to include

Oxford Instruments
Industrial Analysis
For more information please email:magres@oxinst.com
UK
Tubney Woods, Abingdon

the determination of Solid Fat Content

Oxon, OX13 5QX, UK(SFC), by the addition of a hydrogen probe

Tel.: +44 (0) 1865 393 200(10 mm) and conditioning/tempering

Fax: +44 (0) 1865 393 333

hardware as detailed in the AOCS/ISO
SFC protocols.

Room 1/E, Building 1
Xiangzhang Garden

NMR

Using Nuclear Magnetic Resonance to
Test Fat Content in Foods

Case Study

No. 248 Donglan Road

How one contract laboratory dramatically increased sample throughput
The quickening pace of business caused
one of Europe’s leading independent testinglaboratories to seek an alternative to thestandard solvent extraction/acid hydrolysis(Soxhlet) method for testing the amount of fat
in a variety of foods. This contract laboratory,
with numerous sites throughout the UK and
Ireland, provides quality control analyticalservices to the food industry. By convertingfrom the wet chemistry method to an MQC
benchtop nuclear magnetic resonance (NMR)
analyzer for measuring fat content of foods,
the lab reaped significant economic andenvironmental benefits. The box on the rightis a brief overview of NMR’s advantages overother secondary methods.

China

Shanghai 201102, China

Key features of NMR• Can be calibrated to cover a concentration
range from 0.5 to 100 percent fat• Primary calibration can be produced using

Tel: +86 21 6073 2925

a single fat sample• Requires infrequent recalibration• Sample measurement time is short• Minimal sample preparation necessary• No solvents are required• Excellent for bulk measurements• Insensitive to sample granularity andFax: +86 21 6360 8535

product additives• Non-destructive, facilitating repeatability
measurements

USAStandard wet chemistry methods result in bottlenecks
Customers send foodstuff samples to this contract quality

reducing throughput and affecting the lab’s ability to deliver

control laboratory, which has a specialty in fast turnaround

its promised rapid analysis service. The process is also rather

service. A typical request includes five or six measurements,

cumbersome, can be inaccurate, and requires highly skilled

including fat (oil) content. The Soxhlet method used for the

personnel. In addition, many of the hazardous chemicals

oil measurement is slow, with measurements taking as long

used are becoming increasingly unacceptable according to

as 6 hours. This situation led to serious bottlenecks that wereinternational environmental standards.

300 Baker Avenue, Suite 150
Concord, Mass 01742, USA
Tel: +1 978 369 9933
Fax: +1 978 369 8287

Case Study: Fat in Food

SNack

Measurement of Oil Content in Dried Snack Foods

Application Note 2

Summary
chemistry methods+• No hazardous solvents required; nohazardous waste produced• Easiest, most reliable technique available;of the often hazardous chemicals used are becoming increasingly
unacceptable according to international environmental standards.
Despite these issues, solvent extraction continues to be used as a

Measuring the oil content of dried snack foods is essential

Maintenance and consumables also add significantly tofor quality control to ensure that the products meet their

the cost of ownership. For example, although Supercriticalnutritional values specifications. The amount of oil used is also

Fluid Extraction (SFE) is reasonably fast, it requires highimportant in terms of the significant cost of the raw material

maintenance and the cost of compressed CO2 used to extract

and the effect it may have on the texture and perceived

oil is also significant. Near Infra-Red (NIR) is commonly used

quality of the product.

for on-line monitoring but is difficult to apply on opaque

Advantages of NMR

samples as it can only scan the surface. It is also complex tocalibrate as measurements are sensitive to product granularity

Solvent extraction techniques are commonly used forand spices, and therefore it is difficult to maintain accurate

determination of fat content. However, they tend to be

results on a large variety of product types. For that primaryslow, laborious, inaccurate and require skilled personnel. In

reason, NIR has limited applicability for the quality control ofaddition, many of the often hazardous chemicals used areoil content in snack foods.

becoming increasingly unacceptable according to international
environmental standards. Despite these issues solvent
extraction continues to be used as a reference measurement

In contrast, Nuclear Magnetic Resonance (NMR) provides a simple,
accurate and inexpensive measurement of oil content in snack
foods which is routinely used in factories around the world.

for quality control.
MethodInstrumental methods are often referred to as secondary
techniques since they are usually set up to match the results
produced by solvent extraction. To provide a result equivalent

Benchtop NMR detects the signal from oil and distinguishes itfrom signals from solids and bound water (<10% moisture).

to the traditional extraction techniques, secondary techniques
require a calibration against the reference technique used.

0 to 100% fat (oil)• NMR is very stable over the long-term, therefore requires little

Solvent extraction techniques are commonly used for determination

Application• It can be calibrated to cover a concentration range from
• A primary calibration can be produced using a single sample

of fat content. However, they tend to be slow, cumbersome andinaccurate, and require highly skilled personnel. In addition, many

Not including sample conditioning time

Advantages of benchtop NMRof products. Thus, accurate measurements of the fat and oilcontent enable the manufacturers to achieve higher standards in

Method• Simple linear calibration; no chemometrics• Insensitive to sample form and additives

Application Note 17(e.g. carbohydrates). In addition, the fat and oil content may
significantly affect the texture, perceived quality and flavour

nutritional characterisation and quality control of foodstuffs.

suitable for unskilled operators – simple,
intuitive visual software+

Fat and oil content is an important measurement of nutritional
value and product quality for many foodstuffs. In particular,
this value is widely used to determine energy content andto calculate the proportion of other components in foods• Up to 250 times faster than wet

fat

Determination of Fat and OilContent in Foodstuffs

of fat (oil)recalibration• The sample measurement time is short (typically 20 seconds)• Minimal sample preparation is required• It is virtually insensitive to sample matrix granularity and1additives such as spices, flavours, colours and salt

• The NMR technique is non-destructive, so repeatability
measurements can be made conveniently

NMR measurements are temperature sensitive. Care is required
to ensure that the entire sample is within the measurement

and margarine industries. It is important that raw materials arecharacterised according to their melting profile, and rapid andvolume of the tube as any sample smeared on the walls of the
tube contributes to the sample weight, but not to the signal,
leading to erroneous results. The Indirect Method therefore has

convenient methods are required for doing this.
The traditional method for measuring SFC has been dilatometry,
but this is now regarded as slow, inaccurate and cumbersome.
For a number of years, Nuclear Magnetic Resonance (NMR) has
been the method of choice for determination of SFC.

Advantages of benchtop NMR• Complies with all internationally-accepted official direct
methods for SFC measurement: AOCS Cd 16b-93;
ISO 8292-1; and IUPAC 2.150• NMR measurement time is short (typically 6 seconds) but
sample tempering is required (see below)

Calibration and Results

Instrumental methods are often referred to as secondary techniques
since they are usually set up to match the results produced by

A calibration can be generated using either one 100 % fat (oil)• The NMR technique is non-destructive, so repeatability

sample or a set of 3-6 samples of real products with predefinedfat (oil) contents spanning the range of concentrations of• Standards are available for calculation of f-factor (see below)

interest. Figure 1 shows a calibration for foodstuffs with fat
contents ranging from 2.1 to 40.2 % by mass. Samples of driedmacaroni cheese, baked cheese, chicken powders, chicken• NMR is very stable over the long-term, therefore requires

solvent extraction. To provide a result equivalent to the traditional
extraction techniques, secondary techniques require a correlation
against the reference technique used. Although they are fast andeasy to maintain, many secondary techniques need to be calibrated
and maintained regularly. Also, maintenance and consumables
add significantly to the cost of ownership. For example, although
Supercritical Fluid Extraction (SFE) is reasonably fast, it requires highmaintenance and the cost of compressed CO2, used to extract oil isalso significant. Near Infra-Red (NIR) is commonly used for on-line

measurements can be made conveniently

and thereafter for routine quality control checks
little re-calibration

a number of extra complexities.
In contrast, the Direct Method takes measurements of both thesolid and liquid components in the samples, and calculates theratio between them. Measurement of NMR signals from solids
can generally only be carried out on pulsed NMR instruments
operating at 20MHz or above, therefore the Direct Method islimited to such instruments.
As the Direct Method is a ratio method, it is not necessary
to weigh the samples, and it is not sensitive to sample
temperature or loading, all reasons why the Direct Method is
the most common NMR method of SFC determination.
The Direct Method
The Direct Method works by measuring both the solid andliquid signals from the Free Induction Decay (FID) of the sample.
This is possible because the signals from solids decay much
faster than signals from liquids. It is therefore possible inprinciple to take measurements at two points on the FID

sandwich fillers, milk powders, and meat pastes were used togenerate the calibration in Figure 1. As seen in the figure, NMR• Application software available in a range of languages(see Figure 1 opposite), at one point S, corresponding to thetotal solid plus liquid signal, and another at point L which

gives an excellent linear correlation between the NMR response
and the concentration of fats in the products.

Methodcorresponds to the liquid only signal, after the solid signal has
died away. Simple arithmetic then yields the ratio between the

Figure 1: Calibration
obtained for fat content
in foodstuffs; standard
deviation of the linear
fit is 0.20 % by mass,
correlation coefficient R2= 1.00. Measurements
were made using an
Oxford Instruments
MQC-23 benchtop NMR
analyser equipped witha 26 mm diameter probe.

monitoring but is difficult to apply on opaque samples as it can only
scan the surface. It is also complex to calibrate as measurements are
sensitive to product granularity and additives such as seasoning, and
it is therefore difficult to maintain accurate calibrations on a large
variety of product types. For that primary reason, NIR has limited
applicability for the quality control of fat (oil) content in many foods.
In contrast to the standard wet chemistry methods and various
secondary techniques, low resolution Nuclear Magnetic Resonance(NMR) provides a fast, direct and user friendly method for
determination of the fat and oil content in foodstuffs that can be
operated by a non NMR expert user. This technique is based on
measurement of the NMR response obtained from fat (oil) in the
product, and quantification of the fat (oil) content by calibration.

fat

Application Note 13

The measurement of Solid Fat Content (SFC) in edible oils andfats is an essential measurement in the bakery, confectionery

reference measurement for quality control.

There are two NMR methods for determination of SFC, known
as the Indirect and Direct Methods.
The Indirect Method relies on measuring only the liquid part ofthe sample, and the instrument is calibrated by referencing to
the signal from the sample when fully melted. It is necessary toweigh the samples and a correction needs to be made since thesolid and liquid signals, which is the SFC (SFC=(S-L)*100/S).
In practice, it is not possible to take a measurement at point S,
immediately after the 90º pulse, because the pulse causes the
sample probe to ‘ring’ for a few microseconds during which timemeasurements cannot be made. Instead, the first measurement
is taken immediately after this ringing period (or dead time), ata point S’. Given S’ does not represent the total signal from thesolid and liquid, a correction needs to be applied. It assumes afixed ratio (known as the f-factor) between the points S’ and S,
thus S is determined by measuring S’ and multiplying by f before
completing the rest of the calculation.

For optimal precision, samples should be conditioned at 40°C for atleast 20 minutes prior to the measurements.

1

Although they are fast and easy to maintain, many secondary
techniques need to be calibrated and maintained regularly.

No 2. Oil in Dried Snack Foods

Determination of Solid Fat Content in
Edible Oils and Fats by the Official Direct
Method (AOCS Cd 16b-93)

No 17. Fat & Oil in Foodstuffs

Figure 1: Schematic
diagram showing how
Solid Fat Content is derived
from NMR measurementby the Direct Method.

No 13. Solid Fat Content (SFC)

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