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Determination of Solid Fat Content (SFC) in
Oils and Fats by Spin Track NMR Analyzer
Solid Fat Content (SFC) is the generally accepted analysis of fats and oils in the food industry. The traditional methods for SFC determination are slow, irreproducible and require additional chemicals. Direct measurements of SFC by NMR can be performed quickly and accurately. NMR as a method of analysis has been established by the following standards:
 | AOCS Cd 16b-93 revised in 2000 (in USA)
| ISO 8292 (in Europe) | |
Solid Fat Content determination by NMR is based on direct ratio measurment between the solid and liquid parts of the sample observed in the NMR FID.
After excitation of the sample by 90o RF pulse FID (Free Induction Decay) is detected. The FID is the signal accompanying the relaxation process of hydrogen proton magnetic spins moving back to equilibrium state after they are disturbed by the RF pulse. The FID contains contributions from both solid and liquid parts. The proton spins of the liquid content of the sample relax back to equilibrium much more slowly than those of the solid phase component. Thus, a long lasting signal is observed for the liquid phase protons and a rapid decaying signal is observed for the solid-phase component.
Fig. 1. Principle of SFC Determination Using FID
The SFC value is determined by taking two measurment points on the FID. FID amplitude at point S (corresponding to total solids plus liquids), and at point L (corresponding liquids only). The specific ratio can be found using equation shown on Fig. 1. This ratio is considered to be the SFC value.
An F-factor (f) allows the prediction of the FID amplitude value immediately after RF pulse that is impossible to observe directly due to dead-time of the receiver and the ringing time of the probe. The F-factor increases the measurements accuracy and can be determined during calibration procedure.
The Spin Track Portable NMR spectrometer is an ideal instrument for SFC measurements because of it's fine technical characteristics which make measurements very reproducible and accurate. The small weight and portability allow use of the Spin Track in routine production measurements and in advanced laboratories for complicated analyses. Spin Track meets the requirements of international standards such as AOCS Cd 16b-93, AOCS Cd 16-81 revised in 2000, ISO 8292, IUPAC 2.150.
The volume of the sample is 1-3 ml. SFC measurements cycle to produce a 6 point melting curve using a special container for samples and thermostat:
| investigated compound is melted at 80..100oC
and held for 15 min. 6 samples are prepared.
| temperature of all samples is maintained at
60oC for 5-15 min.
| temperature of all samples is maintained at 0oC
for 60 min.
| Each sample is held at required temperature
for measurement (typically 10oC / 15oC / 20oC
/ 25oC / 30oC / 35oC) for 30 -35 min.
| Every sample is placed into the probe and the
measurement process is started. Full cycle requires 110 min. Every NMR
measurement takes not more then 6 s. It is possible to use only one sample
for whole cycle with consequent holding at all temperatures, but this
approach requires approximately 230 min. | |
The procedure of calibration can be performed using the set of original calibration samples developed by Resonance Systems Ltd.