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

Abstract

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. IntroductionFlavour encapsulation is widely used in the food industry since flavour oils are often volatile and therefore subjected to significant losses during processing of food materials. In general, encapsulation is a technique by which the active core material, e.g. flavour oils, perfumes or pharmaceuticals, is coated by, or entrapped within a second material, referred to as matrix, shell, wall material, carrier or encapsulant to form a core-shell composite structure. The active core can thus be protected from moisture, heat, oxidation or other extreme conditions during storage and processing [1,2]. The release of the active can be triggered by pH change, mechanical stress, temperature, enzymatic activity, time or osmotic forces [3], thereby allowing controlled release of the flavour from the shell at a specific time or under predefined conditions. Therefore encapsulation products are also referred to as delivery systems. Flavour delivery systems have enhanced flavour functionality and performance in applications where stability to long shelf life and heavy thermal processing are required. The determination of the flavour oil con...

Oil droplet size determination in complex flavor delivery systems by diffusion NMR spectroscopy

“…Using those as starting values for the bimodal fitting procedure and after having adjusted the parameter a representing the relative fraction in number of the two populations, usually consistent and reproducible fitting results were achieved. Contrary to YES samples no background signals of the GES matrix could be detected [35] and the values of R do not depend on the diffusion time D in the range between 50 ms and 800 ms (data not shown). The fitting values for Orange GES 1 and Orange GES 2 are reported in Table 2.…”

“…Hence, with standard, liquid-state high-field NMR methodology usually only the liquid part is observable, while the signals of the solid matrix are broadened beyond detection. Nevertheless, for YES it could be shown that the constituents of the phospholipid bilayer which is an integral part of the dried yeast cell wall are still sufficiently mobile to be detectable by high-resolution magic angle spinning NMR spectroscopy (HR-MAS) [35]. This background signal from the yeast matrix overlaps with the signal of the encapsulated oil in static NMR spectra and this is presumably the reason for the observed dependence of the droplet sizes in YES on the diffusion time D. Measurements of empty YES showed that the mobile lipid molecules show non-zero diffusion coefficients (D $ 10 À13 m 2 /s) which supposedly is due to slow diffusion along the phoshoplipid interface.…”

“…Bulk diffusion coefficients of the pure oils used in the model were 1.28 Â 10 À9 m 2 /s for limonene and 1.17 Â 10 À9 m 2 /s for banana flavor oil. Values of flavor oil loading are taken from Hafner et al [35]. Table 1. sample material, therefore offering a much higher sampling; (iv) for TEM the cells are cut through different levels of a quasi spherical yeast cell.…”

“…The bulk diffusion coefficient of pure Orange oil used in the model was 1.20 Â 10 À9 m 2 /s. Values of flavor oil loading are taken from Hafner et al[35].Fig. 7.…”

Testing Tools and Physical, Chemical, and Microbiological Characterization of Microencapsulated Systems

“…1À2000 Fieber et al, 2011Hafner et al, 2011;Kalogeropoulos et al, 2010;Sillick and Gregson, 2012;Sosa et al, 2013. X-ray diffraction Non-invasive, non-destructive, high resolution, threedimensional structure can be seen.…”