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Keywords:

  • calcium;
  • magnetic resonance imaging;
  • NMR relaxometry;
  • whey protein gels

Abstract:  Divalent salts are used commonly for gelation of polymer molecules. Calcium, Ca+2, is one of the most common divalent ions that is used in whey protein gels. Manganese, Mn+2, is also divalent, but paramagnetic, enhancing relaxation decay rates in magnetic resonance imaging (MRI) and can be used as a probe to understand the behavior of Ca+2 in whey protein gels. The objective of this study was to investigate the diffusion of Ca+2 and Mn+2 ions in heat-set whey protein gels by using MRI and nuclear magnetic resonance (NMR) relaxometry. Whey protein gels were immersed in solutions containing MnCl2 and CaCl2 at neutral pH. Images obtained with gels immersed in MnCl2 solution revealed a relaxation sink region in the gel's surface and the thickness of the region increased with time. These “no signal” regions in the MR images were attributed to uptake of Mn+2 by the gel. Results obtained with CaCl2 solution indicated that since Ca+2 did not have the paramagnetic effect, the regions where Ca+2 diffused into the gel exhibited a slight decrease in signal intensity. The relaxation spectrums exhibited 3 populations of protons, for gels immersed in MnCl2 solution, and 2 populations for gels in CaCl2 solution. No significant change in T2 distributions was observed for the gels immersed in CaCl2 solution. The results demonstrated that MRI and NMR relaxometry can be used to understand the diffusion of ions into the whey protein gel, which is useful for designing gels of different physical properties for controlled release applications.

Practical Application:  Design of food systems for delivery of bioactive compounds requires knowledge of diffusion rates and structure. Utilizing magnetic resonance imaging the diffusion rates of ions can be measured. Relaxation spectra could yield information concerning molecular interactions.