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Keywords:

  • dairy gel;
  • in situ quantitative nuclear magnetic resonance spectroscopy;
  • liquid fat content;
  • melting behavior;
  • milk fat

Abstract

Dairy gels (DG), such as yoghurts, contain both solid and liquid fats at the time of consumption, as their temperature rises to anything between 10 and 24 °C after being introduced into the mouth at 4 °C. The mass ratio between solid and liquid fats, which depends on the temperature, impacts the organoleptic properties of DG. As the ordinary methods for determining this ratio can only be applied to samples consisting mainly in fat materials, a fat extraction step needs to be added into the analytical process when applied to DG, which prevents the study of the potential impact of their colloidal structure on milk fat fusion behavior. In situ quantitative proton nuclear magnetic resonance spectroscopy (isq 1H NMR) was investigated as a method for direct measurements in DG: at temperatures between 20.0 and 70.0 °C, the liquid fat content and the composition of triacylglycerols of the liquid phase (in terms of alkyl chains length) were determined. Spectra of isolated milk fat also enable the quantification of the double bonds of triacylglycerols. Statistical tests showed no significant difference between isolated milk fat and milk fat inside a DG in terms of melting behavior: the fat globule membrane does not seem to have a significant influence on the fat melting behavior.

Practical Application

In situ quantitative nuclear magnetic resonance spectroscopy (isq 1H NMR) was used to directly determine the liquid fat content in dairy gels (DG) as a function of the temperature, no preliminary fat extraction being required despite the high water content of DG. This method therefore provides useful information for the formulation of dairy products and the understanding of their sensory characteristics. Isq 1H NMR could also be used to directly quantify the liquid fat content in all foodstuffs containing fat: milk, cream, cheese, chocolate, fish, meat, sauces, eggs, and so on.