The microencapsulation is a widely used technique to protect and add bioactive compounds to food matrices, as it is the case oils rich in omega-3 fatty acids. This type of microcapsules should be physico-chemically analysed to guarantee their adequacy, being the microencapsulation efficiency (MEE) one of the most important determinations. MEE refers the percentage of encapsulated oil in relation to total oil in the microcapsules, being needed the determination of external and total oil in the microcapsules. External oil is normally analysed gravimetrically by extraction with petroleum ether, while an acid digestion followed by an extraction with hexane is carried out to calculate total oil [1], which are time and solvent consuming and tedious, require large amounts of samples, and may degrade oil due to extreme conditions. To solve these drawbacks, this study aims to test 1H-NMR (proton Nuclear Magnetic Resonance), due to its reduce cost and time for analysis, minimal sample handling, and no need extraction to determine total oil in fish oil microcapsules.
For this purpose, 15 mg of microcapsules were dissolved in pyridine and analysed in the NMR spectrometer (Spinsolve Ultra 80, Magritek). Once the spectra have been obtained, a processing sheet and a script were applied to obtain the numerical data from the signals belonging to the hydrogens attached to the alpha carbons of the carbonyl group of all the fatty acids. These data are substituted in a calibration line built from standards, in which a fixed amount of wall material was dissolved and variable amounts of oil were added, this line directly gives the total oil values [2]. Total oil were also determined by the usual procedure [1]. Results did not show significant differences between usual and 1H-NMR methods, indicating the goodness of the proposed technique to quantify oil in oil microcapsules.