Determination of flavour loading in complex delivery systems by time-domain NMR

The determination of the flavour content of a newly developed encapsulation system based on yeast was attempted using time-domain NMR (TD-NMR) and compared to thermo gravimetric analysis (TGA). Flavour content as measured by TD-NMR is systematically higher than by TGA. The constant discrepancy between the two techniques is attributed to the presence of the phospholipidic membrane inside the yeast. These phospholipids also contribute to the NMR signal as was revealed by high field NMR studies under magic angle spinning conditions. The signal obtained for the empty yeast matched the extra-contribution to the signal of the flavoured yeast encapsulation system. A classical glassy encapsulation system was used as a comparison to highlight further the presence of the phospholipids in the yeast system. A two step procedure is proposed to correct the reading of the flavoured yeast for the contribution of the yeast cells themselves. Practical applications: TD-NMR is routinely used for the determination of the liquid content encapsulated in a solid matrix, where the liquid can be any oil, including lipids, or flavour and fragrance oils. As shown in the present study, in order to obtain accurate values of the oil loading, the nature of the carrier material of the encapsulation system must be taken into account. For example, with the conventional TD-NMR method, flavour loading in encapsulation systems in yeast cells is systematically overestimated since the phospholipid bilayer contributes to the NMR signal of the flavour oil. With the two-step procedure presented in this article, by subtracting the baseline value obtained for empty yeast cells, accurate loading values for yeast cell carriers can be determined. The modified testing approach is highly accurate and widely applicable to a variety of liquids including flavours, perfumes or nutritive fish oils encapsulated in solid delivery systems.