Linoleic acid assay

Antioxidant activity is also a measure for substance ability to prevent free radical concentration increment, oxidative stress, and risk for development-related diseases. And for the purpose of measuring antioxidant activity, many assays are applied such as 2,2-diphenyl-l-picrylhydrazyl (DPPH) assay, 2,2 -azino-bis(3-ethylbenzthiazoline-6)-sulfonic acid (ABTS) assay, p-carotene bleaching test, ferric and cupric reducing power, and linoleic acid assay (Akrout et ah, 2011 Chabir et ah, 2011 Jia et al, 2010 Serrano et al, 2011). 

For the assessment of the antioxidant activity of canolol, the 3-carotene-linoleic acid assay as well as the DPPH method was used. Using the 3-carotene-linoleic acid assay model system, rapid discolouration was observed in the absence of an antioxidant. The free linoleic acid radical, formed by abstraction of a hydrogen atom from one of its methylene gronps, attacks the P-carotene molecnles resnlting in the loss of double bonds and its characteristic orange colour. The rate of bleaching of the P-carotene solution was determined by measuring the difference between the initial... 

FIGU RE 17.9 Purified canolol from oil of roasted canola seeds 3-carotene-linoleic acid assay. 

Thompson, S. and Smith, M.T. (1985). Measurement of the diene conjugated from of linoleic acid in plasma by high performance liquid chromatography. A questionable non-invasive assay of free radical activity. Chem. Biol. Interactions 55, 357-366. 

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. 

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acid emulsion (9) was placed in a test tube along with 10 pi of a sample to be assayed, and from this, 200 pi were withdrawn and mixed with 2 ml of 100% methanol and 6 ml of 60% methanol-water.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 ... 

Oxidation of linoleic acid Linolenic acid ABAP Spectrophotometric (assay of conjugated dienes) L14... 

Enzyme Assays. Cytochrome P-450 peroxidase activity was determined by the method of O Brien and Rahimthula (27) as modified by Reddy, et al, with cumene hydroperoxide (CHP), linoleic acid hydroperoxide (LHP) and 15-HPETE as substrates and tetramethyl-P-phenylene diamine (TMPD) as electron donor. Prostaglandin H synthase activity was measured as previously described (19). 

Several fatty acids and derivatives were isolated from the dichloromethane extract of Angelica pubescens Maxim f. biserrata Shan et Yuan (Umbelliferae) by following in vitro 5-LOX and COX-1 inhibitory assays. Linoleic acid showed potent inhibition against PGE2 production from purified COX-1 enzyme. Falcarindiol, which is an acetylenic alcohol, showed higher potency against LOX than COX (Table 3) [122]. Linolenic acid is an... 

An assay which is based on the increase in absorption at 234 nm depends on the fact that the linoleic acid hydroperoxide formed by the action of the enzyme possesses two double bonds in a conjugated system. When arachidonic acid is used as substrate, the maximum is at 238 nm 105). The diene conjugation method, introduced by Theorell et al 91), is sensitive and convenient for kinetic studies, especially when used with a recording spectrophotometer. When preparations of low speciflc activity are used, interference from protein absorption can be a problem. In this case the lipid products can be extracted with hexane. For routine work it is convenient to use Surreys substrate mixture 106). 

Linoleic acid is probably the best substrate for assay. It is readily dispersed at alkaline pH, and at acid or neutral pH it is no more difficult to suspend than the methyl ester or the glyceride. Although some species of lipoxygenase show more favorable action with esters than others, we know of no instance where such enzymes do not also act well on linoleic acid. The poor water solubility of linoleic acid and its changing dissociation in the pH range of interest are a disadvantage and usually require emulsifiers. The sulfate ester of linoleyl alcohol, which does not possess this disadvantage, has been proposed by Allen (108) and appears to be a welcome improvement. 

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. 

Red wines have been shown to have higher antioxidant capacity than rose and white wines when analyzed by a linoleic acid peroxidation assay based on measuring chemiluminescence (Kondo et al., 1999). The higher antioxidant activity was related... 

Grapes, wine and other berry products are acidic, and the anthocyanins are in the flavylium form. A hypothesis that the anthocyanins may be pH-transformed into their carbinol pseudo-base and quinoidal base, or the chalcone, in the intestine and blood system during digestion has been proposed by Lapidot et al. (1999). These compounds have been shown to have antioxidant activity and are also most likely absorbed from the gut into the blood system. The pseudo-base and the quinoidal base of malvidin and malvidin-3-glucoside remained as very effective antioxidants, both when tested by a linoleate-oxidizing assay and by a microsomal lipid peroxidation assay. 

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