NMR

Using Nuclear Magnetic Resonance toTest Fat Content in Foods

Case Study

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 andIreland, 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.

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
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 andproduct additives• Non-destructive, facilitating repeatability
measurements

Standard 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 ratherservice. 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 thepersonnel. In addition, many of the hazardous chemicals

oil measurement is slow, with measurements taking as long

used are becoming increasingly unacceptable according toas 6 hours. This situation led to serious bottlenecks that wereinternational environmental standards.

Using Nuclear Magnetic Resonance to Test Fat Content in Foods

Alternatives investigated to speed testing throughput
The lab began seeking a rapid technique that would

In contrast to the standard wet chemistry methods and various

improve turnaround time without increasing operating

secondary techniques, low ﬁeld nuclear magnetic resonancecosts, but would also be comparable to the industry(NMR) provides a fast, direct and user friendly method forstandard Soxhlet technique.

determination of the fat and oil content in foodstuffs. The

There are a number of analytical methods that can be used
to conduct the testing. Such 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 to the traditional extractionobtained from fat in the product, and quantiﬁcation of thefat content by simple and direct calibration without the use ofchemometrics. The instrument is extremely easy to operate anddoes not require the use of skilled chemists or NMR specialists.

techniques, secondary techniques must be correlated against

NMR can be calibrated to cover a concentration range fromthe reference technique used. Although they may be fast in

0.5 to 100 percent fat. The user can produce a primaryuse, many secondary techniques need to be calibrated andcalibration using a single sample of fat. NMR is very stable overmaintained regularly. Maintenance and consumables add

the long-term, and therefore requires infrequent recalibration.

signiﬁcantly to the cost of ownership.

Sample measurement time is short, typically about 20 seconds,

For example, Supercritical Fluid Extraction (SFE) is reasonably
fast, but it requires high maintenance and the cost ofcompressed CO2 that is used to extract oil is also signiﬁcant.
Near Infra-Red (NIR) is sometimes used, but it is generally

2technique is based on measurement of the NMR response

allowing a high throughput of samples and efﬁcient laboratory
operation. Minimal sample preparation is required because
the entire sample is normally loaded into a tube and measured
directly, and there are several different size tubes available.

sensitive to the surface rather than the bulk of the sample,

With NMR, no solvents are required since the sample isand has substantial calibration and calibration maintenanceanalyzed in its natural state. The instrument facilitates bulk

issues. NIR calibration is complex because measurements

measurement; the signal is generated from the whole sample,

are sensitive to product granularity and other physicalensuring that the result embodies everything inside the sample,

characteristics and can be affected by additives such as

not just on the surface. NMR is virtually insensitive to sample

seasoning, making it difﬁcult to maintain accurate calibrations

granularity and such additives as spices, ﬂavors, colours and salt.

on a large variety of product types. This gives NIR limited

Finally, unlike Soxhlet, the NMR technique is non-destructive, soapplicability for the quality control of fat content in foodstuffs.

any required repeatability measurements can be made easily.

Fat content in food

NMR selected to solve throughput
challenges

Table 1Comparison of wet chemistry and NMR-MQC instrument

After reviewing the potential alternative solutions to bottlenecks
associated with fat measurements, the laboratory contactedSample

Given fatcontent %(wet chemistry)

Measured fatcontent %(NMR – MQCinstrument)

Baked cheese

6.1

5.8

Muesli

2.3

2.2

Milk Powder

2524.2Chicken powder

40.2

40.1

Garlic Bread16.1

16.0

Macaroni cheese

2.8-3.4

3.4

Meat

9.9

9.2

Sandwich ﬁller

21.7

21.6

Oxford Instruments, which offers a benchtop NMR instrument
widely used in industry to measure the oil content in foodstuffs
and oil seeds. Oxford Instruments recommended its powerful
but compact MQC benchtop NMR analyzer for this application
because it offers the analyst the beneﬁts of accurate quantitative
results, combined with sampling ease and convenience.
To verify whether the MQC NMR instrument would meetthe laboratory’s needs, applications specialists from Oxford
Instruments collected and tested samples of some of thefoods the lab typically analyzes and compared NMR
measurements on dried samples with fat measurement values
obtained with the Soxhlet method also after oven drying.
The goals of the testing process were to analyze 80 percent ofsamples using the MQC NMR instrument, achieve correlation
to within 5 percent of the wet chemistry method, and achievea repeatability of within 5 percent.
Applications specialists sampled a range of foods, with fat
contents ranging from 2.1 to 40.2 percent by mass, including

As shown on Table 1, the NMR results compared very closely

baked cheese, muesli, milk powder, chicken powder, triﬂe,

to wet chemistry.

garlic bread, macaroni and cheese, meat, and chicken sandwich
ﬁller. Sampling was conducted using an Oxford Instruments
MQC-23 benchtop NMR analyzer equipped with a 26 mm
diameter probe.

3

Fat content in foodFigure 1
Fat (Oil) Content in Foodstuffs
Figure 1 shows a calibration for thesamples, indicating an excellent linear
correlation between the NMR response
and the concentration of fats in theproducts. Instrument repeatability wastested by measuring one sample tentimes. Each sample was conditioned byplacing it in a controlled-temperature
heating block at 40 ºC for 20 minutes
prior to measurement. NMR istemperature sensitive, and with astabilised magnet temperature of40 ºC, repeatability and precision areoptimised by pre-conditioning thesample at that temperature.
In addition, some samples must be
heated to melt the fat so it becomesvisible to the NMR.
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 analyzer equipped with a 26 mm diameter probe.

Table 2 Results of instrument repeatability test
Given fatcontent %(wet chemistry)
16.1

Results (%) of Repeat NMR Measurements

15.79

15.80

15.80

15.81

15.82

15.81

15.82

15.82

15.83

15.81

MeanValue%Standard
Deviation%

15.81

0.01

Table 2 illustrates the repeatability test results, which were well within the anticipated range.

4Fat content in foodThroughput results achievedLaboratory managers reported that the testing results exceeded

Since there is a slight calibration drift over about six months totheir expectations, and the group purchased an MQC low-ﬁeld,

a year, the laboratory will still need to recalibrate periodicallybenchtop NMR analyzer. Currently, about 90-95 percent of theagainst the primary technique or with set-up samples suppliedlaboratory’s samples are run on the MQC instrument and the labby Oxford Instruments. During installation, set-up samples

has increased its efﬁciency because of the rapid measurement

can be made to physically capture and maintain the originalcapability.

calibration, saving time during instrument recalibration. They

Table 3 compares the number of analyses per hour and the skills
required for the NMR technique versus that of Soxhlet. According
to Kulsum Jassat, sales manager for the UK and Europe,“Throughput has increased from 80 to 200
samples per day. With solvent extraction, eachsample took approximately six hours from set-up
to completion, or a rate of about one sample perhour. With NMR, it is usually less than one minuteper sample after sample set-up.” She adds, “Thecompany achieved a return on investment (ROI)
within 5 months of purchasing the instrument.”
The purchase of the NMR MQC instrument allowed thelaboratory to replace four of its Soxhlet units. This signiﬁcantly
reduced the cost of purchase and disposal of solvents, increased

also save time by allowing calibrations to be transferred to othersimilarly conﬁgured Oxford MQC NMR instruments.
While not required by most potential users of NMR instruments,
this particular contract lab chose to get its new fat measurement
method accredited by the United Kingdom Accreditation
Service (UKAS); the national accreditation body that uses a setof internationally agreed standards to assess organizations thatprovide certiﬁcation, testing, inspection, and calibration services.
The lab developed a universal method using a sample blending
process, sample conditioning to ensure the optimal temperature
for reading the NMR signal, followed by analysis using the MQCinstrument. They used hundreds of data samples from Soxhlet
and NMR-MQC to prove that the results obtained from theMQC reproducibly fell within acceptable tolerance. This method
has been UKAS-validated and fully accredited since 2009.

available laboratory space, reduced running costs, achieved
environmental beneﬁts associated with reduced solvent usage,
and facilitated better deployment of laboratory staff.
Table 3 – Measurement comparison

Technique

Solvent
extraction

MQC/NMR

5Analyses per hour at room
temperature

Skills required

1

Highly skilled operator, usually a chemist

60 (1 per minute)Non-skilled operator

Fat content in food

NMR can eliminate quality control bottlenecks

Oxford Instruments
Magnetic Resonance

NMR provides a fast and reliable method to increase throughput for quality control testing of
fat content in foodstuffs. Although past history may have placed the venerable Soxhlet solvent
extraction technique in the role of industry standard, for those seeking to eliminate
quality control bottlenecks, the MQC NMR analyzer is poised to take over the lead.

For more information please email:magres@oxinst.com
UK
Tubney Woods, Abingdon
Oxfordshire, OX13 5QX, UKTel.: +44 (0) 1865 393 200
Fax: +44 (0) 1865 393 333
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No. 800 Nanjing East Road
Shanghai 200001, China
Tel: +86 21 6132 9678
Fax: +86 21 6360 8535
USA300 Baker Avenue, Suite 150
Concord, Massachusetts 01742, USA
Tel: +1 978 369 9933
Fax: +1 978 369 8287

visit www.oxford-instruments.com for more informationwww.oxford-instruments.com

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