Lecithin water systems

W. Harbich, R. M. Servuss, W. Helfrich. Passages in lecithin-water systems. Z Naturforsch 55a 1013-1017, 1978. 

Einally, LDPE SPMDs with grass carp lipid were exposed for 21 d to 14C-2,2, 5,5 -TCB, 14c-3,3, 4,4 -TCB, i c-mirex and i c-fenvalerate, whereas SPMDs with triolein or lecithin were exposed to only " C-2,2, 5,5 -TCB. After 21 d, the largest mass fraction of these test chemicals ( " C-mirex was an exception) was in the triolein. The C-2,2, 5,5 -TCB log triolein-water partition coefficient was 6.01, whereas the " C-2,2, 5,5 -TCB partition coefficients for the grass carp lipid-water and lecithin-water systems were 30% and 35% lower, respectively. Comparison of these data to literature log AlowS of 2,2, 5,5 -TCB showed that the partition coefficients for the grass-carp lipid and the lecithin were not significantly different from median values reported for the log ATow of " C-2,2, 5,5 -TCB. However, the partition coefficient of 2,2, 5,5 -TCB in triolein and water in direct... 

One type of lipid that is dominant in biological interfaces is lecithin, and lecithin-water systems have therefore been examined extensively by different physical techniques. Small s binary system (3) for egg lecithin-water is presented in Figure 2. The lamellar phase is formed over a large composition range, and, at very low water content, the phase behavior is quite complex. Their structures as proposed by Luzzati and co-workers (4) are either lamellar with different hydrocarbon chain packings or based on rods both types are discussed below. 

The L -phase dominates in all lecithin-water systems. Tardieu et al., (1973) found a phase below the chain melting transition in dimyristoyl-lecithin with two sets of long-spacing values, one corresponding to the bilayer thickness and the other considerably larger. The structure was proposed... 

Figure 8.60 Phase diagram of egg lecithin of low water content (a) and of the dimyristoyl-lecithin-water system (b) after Tardieu et al. (1973).

The NaC-lecithin-water system described above is very similar to the conjugated bile salt-lecithin-water system. Minor differences are discussed in (4). 

The phase diagreun of a pure soybean lecithin-water system is shown in Fig. 5.5. The excess water region, relevant to emulsions based on this surfactant, consists of a dispersion of the lamellar hquid crystalline phase in the form of liposomes. 

Fig. 5.5 Binary phase diagram of soybean lecithin-water system.

Little work seems to have been done on thin oriented layers of lyotropic liquid crystals although there is one recent report of preparation of such a layer of the lecithin-water lamellar phase (JO). As indicated by Brochard and de Gennes (II), theories of the hydrodynamics of thermotropic smectic materials can be adapted to describe oriented layers of lamellar liquid crystal in lyotropic systems. 

Pyler (183) reports that hydroxylated lecithin improves dough extensibility. It has been suggested (179) that hydroxylated lecithins are particularly valuable in bakery products because of their apparent synergy with mono- and diglycerides in addition to their high dispersibility in water systems in contrast to the oil solu-bihty of most lecithins. 

FIG. 10 Regulation of the catalytic activity of solubilized enz5unes by variation of the surfactant concentration at a constant degree of hydration in the systems ( ) AOT-water-octane (A) dodecylammonium propionate-water-riiethyl ether/benzene (O) Brij 96-water-cyclohexane ( ) lecithin-water/methanol/pentanol-octane. Dashed lines show levels of corresponding catalytic activities in aqueous solution. (From Ref. 10.)... 

There also exist special situations of W/O systems of the microemulsion type that exhibit rheological behavior very different from that of typical microemulsions. An example of such a case is found in the system lecithin-water-oil. The addition of water to a low viscosity reverse micellar solution of lecithin leads to an increase in the viscosity of the solution by a factor of up to 10 ... 

Monoolein, a common food emulsifier, gives rise to a bicontinuous cubic liquid crystalline phase when added to water, as illustrated in Fig. 4. If a triglyceride oil is introduced into the monoolein-water system, a microemulsion (L2) phase is formed above about 10 wtVo oil as discussed in Sect. II.B. If lecithin is added, the cubic phase is preserved up to about 30 wt% lecithin, beyond which a lamellar (L ) phase is formed [8]. Adding a bile salt, e.g., sodium taurocholate, in sufficient amount will convert the cubic phase to a micellar solution (L,) [9]. 

The effect of adding various lipids to monoolein was discussed above. These lipids are soluble in either water (bile salt) or oil (triglyceride) or hardly soluble at all (lecithin). If a substance that is soluble in both water and oil, e.g., propylene glycol, is added to the monoolein-water system, the cubic liquid crystal undergoes a transition to a sponge or L3 phase [13], as shown in Fig. 5. The structure of the sponge phase has been described as a melted bicontinuous cubic phase [14]. 

One food-grade system that has received much attention as a microemulsion vehicle is the lecithin-triglyceride oil-water system. It is difficult, however, to make a microemulsion with high amounts of oil and water and a small amount of lecithin or any other type of emulsifier [19]. This is not the case if the vegetable oil is replaced by hexadecane, which... 

Fjellesiad (44) discovered that for lecithin-stabilized soja oil-water-systems... 

Ternary systems consisting of lecithin/water/tri-glyceride oil described by Rydhag and Wilton (1981) are dominated by a three-phase region where water, oil and the lamellar L -phase exist in equilibrium. 

Electron-density profiles have been obtained from X-ray studies of many lipid-water systems in the lamellar phase. Fig. 9.30 shows an electron-density profile for a bilayer consisting of lecithin and cholesterol at a 3 2 molar ratio and 100% relative humidity (Franks, 1976). The main features of the profile are two electron-density peaks, in this case about 4.4 nm (44 A) apart, corresponding to the phosphate of the lecithin head-groups, and a pronounced minimum in the electron density at the centre of the bilayer due to the lipid hydrocarbon chain, in particular, the terminal methyl groups. The shoulders, about 1.1 (11 A) from the bilayer... 

Lactoferrin is a glycoprotein found in mammalian milk that tightly binds two ferric ions producing an iron complex more physically and chemically stable than the uncomplexed protein. Bovine lactoferrin inhibited oxidation in com oil-in-water emulsions and lecithin liposome systems (Table 10.8). At the same molar concentration, lactoferrin was less effective than EDTA in inhibiting hydroperoxide formation in a com oil emulsion. This lower antioxidant activity of lactoferrin may be explained by its partial iron saturation and lower affinity for ferric ions. The formation constant for ferric-EDTA is 1.3 x 10 compared to 10 ° for the ferric-lactoferrin complex. Lactoferrin was a better iron chelator in the liposome than in the emulsion systems. Inhibition in liposomes with iron-lactoferrin mixtures was in the order 1 2 > 1 1 > 2 1. This order suggested that lactoferrin also chelated metal impurities as well as added iron to inhibit lipid oxidation. Lactoferrin did not inhibit the copper-catalysed... 

From Huang et al. (1999). Oil-in water emulsions were prepared with 10% corn oil and 1% lecithin emulsifier. Liposomes were prepared with 1% lecithin. Both systems were made up in phosphate buffer (25 mM) (pH 6.6) and oxidized at 50°C. Inhibition values were taken after 2 days for runs with lactoferrin and lactoferrin + EDTA, and after 3 days for runs with Fe and Fe + lactoferrin, and for all liposome runs. 

Fig. 63. The quaternary system cholic acid-lecithin-sodium cholate-water. Expressed as wt%. The tetrahedron at the left represents this quaternary system. HC, cholic acid L, lecithin NaC, sodium cholate W, water. Also a, lamellar liquid crystalline phase b, cubic liquid crystalline phase c, hexagonal liquid crystalline phase d, micellar phase. The shaded areas represent four sections of the quaternary system, taken at different proportions of cholic acid and sodium cholate. These sections are from top to bottom cholic acid-lecithin-water 50% cholic acid 50% sodium cholate-lecithin-water lecithin-water. Note that the top triangle HC-L-H2O has only the lamellar liquid crystalline phase (42).

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