In Situ Quantitative Proton Nuclear Magnetic Resonance Spectroscopy Analysis Of Milk Fat Fusion

Abstract

In situ quantitative proton nuclear magnetic resonance spectroscopy, a fast and easy to implement method, was applied to the study of milk fat melting between 20.00 °C and 70.00 °C. Several milk fat fractions (high melting point, intermediate melting point and low melting point) were investigated, both as isolated fractions and inside dairy gels. Two “fusion indexes” FCH3FAR and FCH2FAR were defined from methylene and methyl protons resonances of fatty acid residues in order to determine the liquid fat proportion and the composition of triglycerides (TG) (in terms of length of alkyl chains of TG) for a temperature T. Modeling the variation of these indexes in function of temperature by a Gauss error function leads to the determination of the distribution of TG in function of their fusion temperature. Statistical tests performed on experimental data showed no significant differences between isolated milk fat and milk fat inside a dairy gel in terms of melting behaviour. In this assumption, it has to be deduced that nucleation sites brought by dairy gel casein network have no significant influence on the fat melting behaviour, especially on the liquid fat proportion. This new method of direct analysis of dairy gels helps to understand the influence of the quantity and composition of TG on the making of milk gels as well as on the release of milk fat flavor compounds. It can also be used to study fat melting behaviour in other low-fat content food products with no preliminary fat extraction, as milk, cheese, chocolate….