Linoleic acid emulsion

Azuma K, Ippoushi K, Ito H, Higashio H and Terao J. 1999. Evaluation of antioxidative activity of vegetable extracts in linoleic acid emulsion and phospholipid bilayers. J Sci Food Agric 79(14) 2010-2016. 

Kristensen, L. and Andersen, H.J. 1997. Effect of heat denaturation on the pro-oxidative activity of metmyoglobin in linoleic acid emulsions. J. Agric. Food Chem. 45 7-13. 

Assays for Antioxidative Activity Spectrophotometric and polarographic (9) assays were utilized to monitor levels of antioxidative activity. In the spectrophotometric assay, a 2-ml portion of linoleic acid emulsion (9) was placed in a test tube along with 10 pi of a sample to be assayed, and from this, 200 pi were withdrawn and mixed with 2 ml of 100% methanol and 6 ml of 60% methanol-water. The remainder of the 2 ml of emulsion and sample mixture was then incubated at 37°C for 15 to 20 h. Meanwhile, the absorbance of the methanol solution to which the 200 pi of sample had been added was measured at 234 nm. After incubation, the absorbance of 200 pi of the emulsion and sample mixture was also measured at 234 nm in the same manner. Antioxidative activity (A.O.A.) was calculated using the equation ... 

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. 

The antioxidant activity of phenols used and standards was determined according to die ferric thiocyanate method with minor modifications. Each sample of treated wool (200 mg) was mixed with 2 mL distiUed water and 5 mL linoleic acid emulsion (0.02 M, pH 7.0) and 5 mL phosphate bufier (0.2 M, pH 7.0). Linoleic acid emulsion was prepared by mixing 0.5608 g of linoleic acid with 0.5608 g of Tween 20 as emulsifier, and 100 mL phosphate buffer (0.2 M, pH 7.0), and then the mixture was homogenised. The reaction mixture was incubated at 37 C. Aliquots of 0.1 mL wm taken at different intervals during incubation. The degree of oxidation was measured by sequentiaUy adding 4.7 mL ethanol (75%), 0.1 mL ammonium diiocyanate (30 %), 0.1 mL sample solution and 0.1 mL ferrous chloride (0.02 mg, in 3.5% HCl). The mixture was... 

Table 10.7. Prooxidant activity of free iron, hemin and metmyoglobin, before and after heating, in linoleic acid emulsions"...

Linoleic acid emulsion Trolox > a-tocopherol = camosol > carnosic acid (2)... 

B) TEARS Measurement in the Model Lipid Emulsion System. The TEARS generated in a model linoleic acid emulsion system containing Glu-Lys and Fru-Lys MRPs, in the absence of metal ions, is presented in Table 2 i.e., %AO). Unlike the oxygen depletion measurements which identified both the antioxidant or prooxidant activity of individual Glu-Lys and Fru-Lys model experiments, no potential prooxidant effect of MRPs was identified using the TBARs measurement. As such, all Glu-Lys and Fru-Lys MRPs derived from different experimental conditions, reduced lipid peroxidation in the lipid emulsion system. However, despite the finding that all experiments show antioxidant activity as assessed using TBARs endpoint measurements, many of the products derived from different Fru-Lys experiments exhibited relatively low e.g. below 5%) antioxidant activity. 

The essential fatty acids in humans are linoleic acid (C-18 2 N-6) and a-linolenic acid (C18 3 N-3). Arachidonic acid (C20 4 N-6) is also essential but can be synthesized from linoleic acid. Administration of 2% to 4% of total daily calories as linoleic acid should be adequate to prevent essential fatty acid deficiency in adults (e.g., infusion of 500 mL of 20% intravenous lipid emulsion once weekly).7 Biochemical evidence of essential fatty acid deficiency can develop in about 2 to 4 weeks in adult patients receiving lipid-free PN, and clinical manifestations generally appear after an additional... 

Dopamine, a strong water-soluble antioxidant, was identified in banana fruit (Musa cavendishii) by Kanazawa and Sakakibara (2000). Banana fruit contained high levels in the pulp and peel 2.5-10 mg/100 g and 80-560 mg/100 g, respectively. A banana water extract was reported to suppress the autoxidation of linoleic acid by 65-70% after a 5-day incubation in an emulsion system, as determined from peroxide value and thiobarbituric acid reactivity (Kanazawa and Sakakibara 2000). 

This assay, developed by Taga and others (1984), is based on the coupled oxidation of (3-carotene and linoleic acid. The method estimates the relative ability of antioxidant compounds to scavenge the radical of linoleic acid peroxide (LOO ) that oxidizes (3-carotene in the emulsion phase. 

Spin trapping has also been applied to the investigation of lipid peroxidation catalysed by myoglobin in linoleate emulsions,204 as well as the oxidation of phospholipids in low-density lipoproteins (18.1) by HOC1.205 Hiramoto et al. have shown that, by quenching the attacking radicals, linoleic acid can protect DNA from oxidation.206 Lipid peroxidation has also been monitored by spin labelling.207... 

Linoleic acid and alpha-linoleic acid are essential fatty acids that are provided in any long-term parenteral nutrition by administering fat emulsions at least twice a week. Fatty acid deficiency is a common complication of severe end-stage liver disease. The ability of short-term intravenous lipid supplementation to reverse fatty acid deficiencies has been studied in patients with chronic liver disease and low plasma concentrations of fatty acids (914). Shortterm supplementation failed to normalize triglycerides. 

Linoleic acid is used in topical transdermal formulations, in oral formulations as an absorption enhancer, and in topical cosmetic formulations as an emulsifying agent. It is also administered in parenteral emulsions as a dietary supplement. 

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