Comparison of ultrasonic and pulsed NMR techniques for determination of solid fat content |
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Authors: | Anand?Pal?Singh D?J?McClements Email author" target="_blank">A?G?MarangoniEmail author |
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Affiliation: | (1) Center for Food and Soft Materials Science, Department of Food Science, University of Guelph, N1G2W1 Guelph, Ontario, Canada;(2) Biopolymers and Colloids Research Laboratory, Department of Food Science, University of Massachusetts, 01003 Amherst, Massachusetts |
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Abstract: | In this work an ultrasonic velocity technique was compared to direct pulsed NMR (pNMR) spectroscopy for the determination
of the solid fat content (SFC) of anhydrous milk fat (AMF), cocoa butter (CB), and blends of AMF and CB with canola oil (CO)
in the range 100 to 70% (w/w). In situ measurements of ultrasonic velocity were carried out during cooling (50–5°C) and heating (5–50°C) of the fat samples, and
SFC values were calculated. The SFC were also determined simultaneously by pNMR. Peak melting temperatures determined by DSC
were used as an indicator of the polymorphic state of the different fats and fat blends. Estimates of SFC obtained using pNMR
and ultrasonic velocimetry did not agree. Our results suggested that ultrasonic velocity was highly dependent on the polymorphic
state of the solid fat. Ultrasonic velocity in fat that contained crystals in a more stable polymorphic form was consistently
higher than in fat that contained crystals in a less stable polymorphic modification. A high attenuation of the signal was
observed in milkfat and CB at lower temperatures, particularly after sitting for 24 h. This high attenuation could be a product
of scattering by crystallites or by microscopic air pockets formed upon solidification of the material, or it could be due
to high ultrasonic absorption associated with phase transitions. This research highlights some of the problems associated
with applying ultrasonics to the determination of SFC. |
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Keywords: | Cocoa butter crystallization melting microstructure milk fat polymorphism SFC ultrasonic velocity |
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