Pulsed nuclear magnetic resonance pNMR

Pulsed nuclear magnetic resonance (pNMR) has become the preferred method for measuring the percentage of solid fat in a partly solidified fat sample in most parts of the world because of its speed, precision and utility (Kaylegian and Lindsay, 1994). In contrast to dilatometry, pNMR measures the true solid fat content (SFC) rather than an index of this. 

Solid Fat Content Many methods for measuring SFC have been developed. These include dilatometry, calorimetry, and pulsed nuclear magnetic resonance (pNMR). Dilatometry and calorimetry use measurements of volume or heat content ratios between the completely liquid and the completely solid states (42). Dilatometry and calorimetry methods are time consuming and tend to be applicable only when the SFC is less than 50% (42). Therefore, pNMR has become the most commonly used method for SFC determination. 

The dilatometric method is time-consuming and subject to the bias introduced by the convention described. More recently pulsed Nuclear Magnetic Resonance (pNMR) has been used to measure the relative amounts of liquid and solid fat in a sample, based upon the difference in rates of relaxation of protons in the two phases after the sample has been pulsed (AOCS Method Cd 16-81). With proper calibration this gives a direct determination of the percentage of solid fat, and the results are termed sohd fat content (SFC). The analysis takes less time than dilato-metry, but the equipment is more expensive. 

Fig. 2. Cooling curves for samples in pulsed nuclear magnetic resonance (pNMR), tur-bidimetric, light-scattering, and image analysis experiments.

The solid fat content (SFC) profile may be used to compare the physical properties of the various fractions. SFC can be measured by using one of the standard pulsed nuclear magnetic resonance (pNMR) methods [55,56]. In Figure... 

Solid fat contents (SFCs) of the samples were measured by pulsed nuclear magnetic resonance (pNMR). The number of hydrogen nuclei in the liquid and the total number of hydrogen nuclei in liquid and solids were measured. The percentage of solid content is given by the equation... 

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