C. Characterization of linseed fish oil emulsions (LSFE) oxidative stability and structural changes during thermal oxidation, using H1 LF-NMR energy relaxation time analysis and supportive methodologies.
LSFE was prepared, as described in the Material and Methods section by the addition of fish oil rich in the long chain PUFAs EPA and DHA. The chemical and morphological structure of LSFE is characterized by oil bodies vesicles with an amphiphilic interface surface and lipophilic core encapsulating PUFA-rich linseed and fish oil. The1H LF-NMR energy relaxation TD fingerprinting for LSFE before (T 0) and after thermal oxidation at 55 oC for 96 hours (T 96 h) are shown in Fig. 6.
It is interesting to note that before and after thermal oxidation at 55oC for 96 hours only minimal phase separation could be observed in the LSFE samples (see supplemental 1). The analysis of Fig. 6 shows that LSFE T 0 h and LSFE T 96 h have similar characteristics T1 and T2 energy relaxation time graphics. The 1D T2 energy relaxation time graphics of LSFE T 0 h and LSFE T 96 h shows fours small peaks corresponding to the four segmental motions of the PUFA-rich oil molecules within the core of the oil bodies emulsion and one peak of higher intensity related to the oil energy relaxation time in the surface of the oil bodies vesicles. The 2D T1-T2 relaxation time graphics of LSFE T 0 h and LSFE T 96 h shows small peaks assigned as the PUFA-rich oil molecules within the OB core and one peak of higher intensity related to the energy relaxation time in the OB’s vesicle surface.
In Table 5 the T1 and T2 energy relaxation times values of LSFE T 0 h and LSFE T 96 h are tabulated. It can be seen that the relaxation time values of T1 and T2 of the main peak assigned as the vesicles surface are somewhat lower for LSFE after the thermal oxidation of 96 hours as are most of the other peaks that could be observed. These data are in the same general pattern of the results obtained for LSE described above (Table 3).
Microscopic images of LSFE oil bodies emulsion of non-heated fresh sample and after 96 h of thermal heating (Fig. 7), show some increase of oil bodies after the heating period. Interesting to note that in both cases before and after heating only minimal phase separation could be observed in the LSFE samples. A similar pattern for LSFE (Table 6), some increase of droplet particle size distribution from 1374 to 1951 nm for fresh and heated sample, respectively was obtained. Zeta potential values were -27.3 and -25.1 mv for the two samples, suggested of a moderate rate of stability of the emulsion samples. The rate of self diffusion was slightly reduced from 2.902 to 2.734 10^-9m*m/s, respectively. All these supportive analyses well correlated with the T1-T2 energy relaxation time information obtained from NMR analyses (Fig. 6) that is also summarized in the small increase of T1/T2 ratio.