Lipid stability measurements

The oil stability index (OSI) method provides results in a matter of hours instead of months (required for studies done at ambient temperatures). These OSI results are useful as comparative measures of oxidative stability, i.e., to determine the effect of a treatment or antioxidant compared to a control sample. Meaningful predictions of the actual shelf lives of specific commodities require that such shelf life studies be performed at ambient conditions. If only accelerated tests are to be performed, two or more tests based on different principles of lipid oxidation measurement should be conducted the effect of accelerated storage temperature should also be investigated. 

FRAP measurements of surface diffusion in surfactant or lipid-stabilized thin films... 

The zeta potential of the formulations was determined by Doppler velocimetry and PCS on a Zetasizer 4 (Malvern Instruments, U.K.), without further dilution. The zeta potential of LC-AmB under these conditions was —44 mV, slightly lower than that measured for the same lipid composition without AmB, —55 mV, but remaining consistent with colloidal stability. This reduction in the absolute value of the zeta potential could be due to the presence of AmB at the surface, because free AmB dispersed in water under the same conditions had a less negative zeta potential about —27 mV. 

Figure 4 Effect on the serum stability of the incorporation of 5% cholesterol poly(ethy-lene glycol) (PEG) into cationic lipoplexes [hpopolyamine RPR209120/DOPE1/1, ratio (mol) lipid/DNA = 10 in 150 mM NaCl]. Lipoplexes were incubated in DMEM + 10% SVF, at 37°C, aliquots were regularly sampled and monitored by dynamic diffusion. Results represent a mean between three measurements. Error bars are not presented to simplify the graph, but differences among PEG, PEG-1, and PEG-2 are significant. Abbreviations PEG, poly(ethylene glycol) DOPE, dioleylphosphatidylethanolamine DMEM, Dulbecco s Modified Eagle Medium.

The complex formation constants presented in Tables 2—4 were measured in water, methanol or ethanol. There is no guarantee, however, that the selectivity sequences thus found will apply in lipid membranes. This being so, it becomes necessary to investigate the stability of a given complex as a function of the embedding medium. 

Entrapment of the enzyme inside the lipid vesicles led to a stabilization of the enzyme against inhibition by externally added Cu + ions, as measured withp-nitrophenyl-D 3-D-glucopyranoside as substrate. 

The improved DPMD" decolorization assay is suitable for water-soluble as well as lipid-soluble antioxidants [33]. A stock solution of DMPD cation radical is diluted to A5i7 5n > =0.7-70.8 and after equilibration at 25°C stabilized with ethanol or an acetate buffer (pH 5.6). The experiment is conducted at 30°C and the absorbance of the reaction mixture is read out after 6 minutes. The measurement values obtained by the method with the cation radical DMPD are comparable with those obtained in the ABTS assay. As the cost of the DPMD is several times lower, it could be successfully used as an alternative for the ABTS assay [33]. 

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