Linoleic acid Lipophilicity

Alpha-tocopherol is a highly lipophilic compound, and is an excellent solvent for many poorly soluble drugs.Of widespread regulatory acceptability, tocopherols are of value in oil- or fat-based pharmaceutical products and are normally used in the concentration range 0.001-0.05% v/v. There is frequently an optimum concentration thus the autoxidation of linoleic acid and methyl linolenate is reduced at low concentrations of alpha tocopherol, and is accelerated by higher concentrations. Antioxidant effectiveness can be increased by the addition of oil-soluble synergists such as lecithin and ascorbyl palmitate. " ... 

The antioxidant activity of a compound depends upon which free radical or oxidant is used in the assay (Halliwell and Gutteridge, 1995), and a different order of antioxidant activity is therefore to be expected when analyses are performed using different methods. This has been demonstrated by Tsuda et al. (1994) in their study of antioxidative activity of an anthocyanin (cyanidin-3-O-p-D-glucosidc) and an anthocyanidin (cyanidin) in four different lipophilic assay systems. Both compounds had antioxidative activity in all four systems, but the relative activity between them and their activity, compared with Trolox, varied with the method used. Fukumoto and Mazza (2000) reported that antioxidant activity of compounds with similar structures gave the same trends, although not always the same results, when measured by P-carotene bleaching, DPPH and HPLC detection of malonaldehyde formation in linoleic acid emulsion. 

A very different type of reaction is represented by the conjugation of xenobiotic alcohols with fatty acids, yielding highly lipophilic metabolites accumulating in tissues. Thus, ethanol and haloethanols form esters with palmitic acid, oleic acid, linoleic acid, and lin-olenic acid enzymes catalyzing such reactions are cholesteryl ester synthase (EC 3.1.1.13) and fatty-acyl-ethyl-ester synthase (EC 3.1.1.67) (71). Larger xenobiotics such as tet-rahydrocannabinols and codeine are also acy-... 

The physical states of lipid systems affect the distribution of antioxidants and influence their activity. a-Tocopherol and Trolox exhibit complex interfacial properties between air-oil and oil-water interfaces that significantly affect their relative activities in different lipid systems (see Chapter 10). In the bulk oil system, the hydrophilic Trolox is apparently more protective by being oriented in the air-oil interface (Figure 10.8). In the emulsion system, the lipophilic a-tocopherol is more protective by being oriented in the oil-water interface. Because of its tendency to form micelles, linoleic acid is not an appropriate lipid for testing antioxidants since their behavior in this substrate would be significantly different from that in foods composed mainly of triacylglycerols. 

TRAP Decay of artificial radical in presence of linoleic acid, electrode end-point or luminol chemiluminescence Not suitable to test lipophilic antioxidants and metal chelators, not sensitive WaynerefaZ. (1985, 1986)... 

The lipophilic a-tocopherol and its hydrophilic analog Trolox also behave quite differently in linoleic acid micelles compared to phosphatidylcholine liposomes. With micelles of linoleic acid in SDS initiated with a water-soluble initiator [2,2 -azobis-(2-amidino propane) dihydrochloride, ABAP], a-toco-pherol was much less active than Trolox (Table 10.16). With phosphatidylcholine liposomes initiated with a lipid-soluble initiator AMVN, a-tocopherol and Trolox had about the same antioxidant activity. Linoleic acid and SDS form mixed micelles in the aqueous phase in which the polar antioxidant Trolox equilibrates more rapidly and becomes more effective than in liposomes. Also, Trolox can efficiently trap radicals from the water-soluble initiator ABAP. 

The lipid peroxidation inhibitory activities of EOs are assessed by the P-carotene bleaching tests (Yadegarinia et al., 2006). In this method, the ability to minimize the coupled oxidation of P -carotene and linoleic acid is measured with a photospectrometer. The reaction with radicals shows a change in this orange color. The P-carotene bleaching test shows better results than the DPPH assay because it is more specialized in lipophilic compounds. The test is important in the food industry because the test medium is an emulsion, which is near to the situation in food, therefore allowable alternatives to synthetic antioxidants can be found. An only qualitative assertion uses the TLC procedure. A sample of the EOs is applied onto a TLC plate and is sprayed with P-carotene and linoleic acid. Afterwards, the plate is abandoned to the daylight for 45 min. Zones with constant yellow colors show an antioxidative activity of the component (Guerrini et al., 2006). 

The esters utilized oleic, palmitic, linoleic, stearic, palmitoleic, myristic, and laurlc acids, but collectively these lipophilic conjugates represented <0.1% of the applied dose. The hydroxyethyl groups of dlpyrldamol (a coronary vasodilator) and mopldamol (a cytostatic agent) are esterified with oleic and palmitic acids (35). These lipophilic derivatives of both drugs are excreted In feces (about 4X of the applied dose for rats and humans). 

Fruits obtained from this species of palm are very rich in fats, including oleic, lauric, myristic, capric, palmitic, stearic (all saturated) and linoleic fatty acids as well as ethyl esters of these fatty acids. The lipophilic constituents also include numerous sterols, diterpenes, sesquiterpenes, triterpenes, carotenoids and high-molecular-weight alcohols (Winston 1999). Water-soluble polysaccharides with high molecular weights are also found in the seed, but not in the widely used liposterolic extracts. 

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