Antioxidants testing

Tea extracts and tea polyphenols inhibit copper- and peroxide-induced oxidation of LDL in vitro (116,123,124). The inhibitory concentration for 50% reduction (IC q) values for inhibition of copper-induced oxidation of LDL by some phenoHc antioxidants are Hsted in Table 7. The IC q for epigaHocatechin gaHate was found to be 0.075 p.mM, which was the most potent of all the phenoHc antioxidants tested (123,124). Similar results have been reported elsewhere (115,116,125,126). 

As everyone knows, plants have been used for centuries in herbalism, homeopathy, and aromatherapy because of their medicinal qualities. The long-term use of plants has led to recent observations about their antioxidant properties (1, 2). Many scientists have observed antioxidant activities in compounds derived from the volatile constituents (3, 4) and essential oil extracts - of plants. They have reported that ingestion of these volatile chemicals can prevent lipid peroxidation, which is associated with diseases such as cancer, leukemia, and arthritis. In the present study, analysis and antioxidative tests on the volatile extract isolated from a commercial beer were performed. Why did we choose beer We chose beer because... 

Josephson (1943) reported that butterfat prepared from butter heated to 149°, 177°, and 204.5°C was extremely stable to oxidation, while that heated to 121 °C oxidized readily when stored at 60°C. When butter oil itself was heated from 121 to 204.5 °C, it also oxidized rapidly. However, the addition of 1% skim milk powder to butter oil prior to heating at 204.5°C for 10 min also resulted in a significant antioxidative effect, which Josephson concluded was the result of a protein-lactose reaction (carmelization). Wyatt and Day (1965) reported that the addition of 0.5% nonfat milk solids to butter oil followed by heating at 200 °C and 15 mm Hg for 15 min caused the formation of antioxidants which protected the butter oil against oxidative deterioration for 1 year, surpassing the effectiveness of many synthetic antioxidants tested. 

A qualitative and quantitative HPLC method for analysis of mixtures of 12 antioxidants was described Grosset et al. (121). For the identification of the components present, gradient elution with a convex profile from 35 65 water-methanol to pure methanol is used, on a Waters 5-/xm C18 column, with UV detector. Propyl gallate was not separated by this system. For quantitative analysis, with UV and electrochemical detectors in series, the water-methanol mixture or pure methanol was used as the eluent, under isocratic conditions, with lithium perchlorate as supporting electrolyte. An applied potential ranging from +0.8 to +1.7 V allows detection of all the antioxidants tested. Both modes of detection were very sensitive, with limits of detection as low as 61 pg. 

Let us now examine the antioxidant test results for the various phenols alkylated by a-olefins. They have been evaluated in several tests, but data are presented in Table III for only four different test procedures, chosen to illustrate the effect of increasing severity of test conditions. The least severe of these is the 140°C. stress-crack life test using a 65-mil thick molded bar. The 160 °C. oven-life test using the same molded bar is somewhat more severe. Increasing severity is shown by the 140°C. oven-life test and the 160°C. oven-life test using 5-mil film test pieces. The relatively thick bars used in the first two tests provide a reservoir of antioxidant to replace that lost from the surface. These tests probably measure the inherent effectiveness of the antioxidant. In the tests using... 

Certain phenolic antioxidants in combination with ultraviolet absorbers improve substantially the light stability of polystyrene. Combinations of this type can be used advantageously to prevent polymer discoloration in indoor fluorescent lamp fixture applications. However, studies of this type require further investigation, and an explanation must be sought for the striking differences in behavior of the various antioxidants tested. 

Most of the studies on the antioxidant activity of SF have been performed using y-oryzanol or the addition of rice bran oil (containing also other components with antioxidant activity), and from those studies it is not possible to evaluate the activities of single compounds. Further, the information obtained on the relative antioxidant activities of the different FSs varies from one study to another (Table 10.2). One reason for this may be that the range of antioxidant tests used in these studies is wide and the results, therefore, are not necessarily comparable. More studies are definitely needed to fully understand the possible differences in the antioxidant activity of different SFs in different oxidation systems. 

Antioxidants added before rendering improve the fat stability. Sims and Hilfman (42) studied the stabilization of lard and edible beef fats during pressure steam rendering. Antioxidants tested included butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate and citric acid combinations, and a mixmre of BHA and BHT. Best results for a given stabihzer level were obtained with the individual phenolics BHA and BHT. Poorer results were obtained with the mixtures in propylene glycol. 

Vegetable oil (none) or antioxidants in vegetable oil were added as ingredients in the raw meat emulsions for bologna manufacture. The antioxidants tested were 500 ppm sodium erythorbate (eiythorbate), 200 ppm sodium nitrite (nitrite), and 0.075% rosemary extract (rosemary). The emulsions were cased, cooked, and irradiated at 3 kGy. Volatile compounds measured die next day, and expressol as square root of peak ar count. The numbers were means of four replicates. Adopted from ref (26). 

The Antioxidant Test procedure for Superoxide is provided by the sup>pher of the test kit (Hipler and Knight, 2001). The amount of sample was optimised to obtain not more than 90% and typically 50% signal inhibition. This signal was then corrected for sample dilution 10 iL of sample was used, however, red wines and rose wines were first diluted with water (1 10) while white wines were not. 

Hipler, B., and J. Knight. (2001). ABEL Antioxidant test kit with Pholasin for Vitamin C type antioxidants. Knight Scientific Ltd., Application note 108. 

Semisynthetic a-tocopherol is a mixture of the diasteroi-somers about configuration 2EJS, A R, and % R. The anti-oxidative effect of the different tocopherols may not be identical. It has been shown in antioxidation tests with foodstuffs that the antioxidative activity of the tocopherols increases in the order 7-, 8-, (3-, and a-tocopherol. Vitamin E occurs principally in wheat germ, vegetable oil, and vegetables. 

The reported and claimed activities of different antioxidants and formulations are difficult to evaluate because of the different testing conditions used. For example, when tested at 45°C, ascorbic acid was less effective in stabilizing soybean oil than ascorbyl palmitate, which was in turn more effective than BHA and BHT, but not as active as PG and TBHQ. TBHQ was the most active of the antioxidants tested (Table 9.4). However, when tested at 98°C under conditions of the active oxygen method (AOM), the relative antioxidant activities of ascorbic acid and ascorbyl palmitate were reversed and ascorbic acid became more active than PG and TBHQ. These results must be interpreted with caution. The peroxide value used to follow oxidation is not reliable when oils are heated at 98°C because a large fraction of the hydroperoxides is decomposed at this temperature (Chapter 7). The peroxide value of 70 used as an end-point is also questionable since flavor deterioration occurs in soybean oil at peroxide values below 10. 

Randonic, A. and M. Milos, 2003. Chemical composition and antioxidant test of free and glycosidically bound volatile compounds of Savory (Satureja montana L. susp. montana) from Croatia. Nahrung/Food, 47(4) 236-237. 

FIA methods based on ferric reducing power similar to the FRAP principle reaction have been used for the determination of ascorbic acid, vitamin E, and total iron. Table 30.1 summarizes most of these studies. Spectrophotometric detection is also used in many of these studies because of the chromogenic effect from Fe oxidation, which changes with complex ligands, such as TPTZ, o-phenanthroline, cyanide, and DPPH. Different FIA manifolds have also been investigated and proposed, from single to multiple lines. Therefore, like other chromogenic antioxidant tests, the FRAP assay has the potential for several flow injection adaptations. 

PE is characterized by a very low water absorption, e.g. HDPE water absorption index = 0.04%. All antioxidants tested by us are insoluble in water, but they are distributed in PE melt perfectly (the classical feature required of any antioxidant [7]). Furthermore, according to the notion of diffusion, in cross-linked struetures such processes are hampered. That is why there is a low probability of the examined antioxidants migration from PEX-A - a conclusion, which is supported by the received experimental results. 

Phosphorus-containing antioxidants, tested as candidates for catalysts. 

The studies referred to above use LDL in an in vitro assay, but the ultimate antioxidant test is whether these compounds work in animals or humans. There are very few examples of an in vivo antioxidant action of a carotenoid in humans. The best recent examples come from studies with children suffering from cystic fibrosis who are known to have relatively low levels of carotenoids in their serum. These patients are supplemented with large amounts of vitamin E, but still show significantly elevated levels of malondialdehyde in their serum. Two groups have supplemented patients with this disease with p-carotene, and in each case, they reported a decrease in the malondialdehyde levels [27, 20] as well as increased resistance of LDL to oxidant stress [27]. 

---