32 FOOD & DRINK TECHNOLOGY
Figure 2 – Fat (Oil) Content in foodstuffs.
Calibration obtained for fat content in foodstuffs; standard deviation of the linear fit is 0.20 per cent 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.
samples, indicating an excellent linear correlation between the NMR response and the concentration of fats in the products.
Instrument repeatability was tested by measuring one sample ten times. Prior to each measurement the sample was placed in a heating block for 20 minutes.
Since the magnet is temperature stabilised at 40°C, precision is enhanced by conditioning the sample at 40°C prior to inserting it into the NMR magnet.
Conditioning samples prior to measurements aids repeatability, since the NMR signal is temperature sensitive.
In addition, some samples must be heated to melt the fat so it becomes visible to the NMR. Te sample only needs to be returned to the block for a further 20 minutes if the
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measurement is going to be repeated on that sample.
Laboratory managers reported that the testing results exceeded their expectations, and the group purchased an MQC low-field, benchtop NMR analyser. Currently, about 90-95 per cent of the laboratory’s samples are run on the MQC instrument and the lab has increased its efficiency because of the rapid measurement capability.
Fig. 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: “Troughput has increased from 80 to 200 samples per day. With solvent extraction, each sample took approximately six hours from set-up to completion, or a rate of about one sample per hour.
“With NMR, it is usually less than one minute per sample after sample set-up.”
“NIR calibration is complex because measurements are sensitive to product granularity and other physical characteristics and can be affected by additives such as seasoning, making it difficult to maintain accurate calibrations on a large variety of product types.”
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