Antioxidants evaluation methods

In fats and oils, the process of oxidation is similar to that oxidation of any other unsaturated organic material and requires an initiation process, in order to generate free radicals from the substrate. As antioxidants inhibit oxidation or autoxidation process, the mechanism(s) involved need(s) to be discussed. Figure 1 explains the relationship of antioxidant activity and oxidation of a lipid as examined by a typical evaluation method. 

Afrormosin, 243, calycosin, 245, and odoratin, 252, have been found to be the antioxidative components of the methanolic extract of A. membranaceus by using the evaluation method on the air oxidation of linoleic acid [243]. Some isoflavonoids have also been determined in root cultures of A. membranaceus by reverse phase HPLC [324]. 

The activity of natural antioxidants is greatly affected by complex interfacial phenomena in emulsions and multi-component foods. The methodology to evaluate natural antioxidants must be carefully interpreted depending on whether oxidation is carried out in bulk oils or in emulsions, and which analytical method is used to determine extent and end-point of oxidation (Chapter 10). To understand and better predict how natural antioxidants may protect foods against oxidation, the following complex questions need to be carefully considered for the judicious choice of antioxidant evaluation protocols a) What are the protective properties of antioxidants b) What substrates are oxidized and what products of oxidation are inhibited c) In a multiphase food system is the antioxidant located where oxidation takes place d) Are there any... 

Each antioxidant evaluation should thus be carried out under various conditions of oxidation, using several methods to measure different products of oxidation related to real food quality. There cannot be a short cut approach to determining the activity of antioxidants. Various testing protocols should consider the following parameters and recommendations ... 

The present study describes antioxidant activity of the eight Okinawan herbs, their constituents and antioxidant evaluation measured by several methods. 

The effectiveness of antioxidants as preservatives for fats and oils is evaluated by determining the rate of peroxide development using the Active Oxygen Method (AOM) (29). The development of a rancid odor is used to evaluate the stabiUty of food items (Schaal Oven StabiUty test) (30). 

Tawa, R., and Sakurai, H. (1997). Determination of four active oxygen species such as H2O2, OH, OJ and 02 by luminol-and CLA-chemiluminescence methods and evaluation of antioxidative effects of hydroxybenzoic acid. Anal. Lett. 30 2811-2825. 

KUMAMOTO M and soNDA T (1998) Evaluation of the antioxidative activity of tea by an oxygen electrode method , Biosci Biotechnol Biochem, 62, 175-7. 

BRAND-WILLIAMS w, cuvELiER M E and BERSET c (1995) Use of free radical method to evaluate antioxidant activity, Lebensm Wiss Technol, 28, 25-30. 

FRANKEL E N and MEYER A s (2000) The problems of using one-dimensional methods to evaluate multifunctional food and biological antioxidants, JSci FoodAgric, 80,1925-41. 

Many different methods have been used to evaluate the antioxidant capacities of isolated molecules, carotenoids, and other natural antioxidants and of foods and food extracts containing antioxidants. It is not the purpose of this chaper to review all the methods, but some general points can be made. First, when using only one test to evaluate the antioxidant capacities of carotenoids, one should be very careful in the interpretation of obtained data. Indeed, different results can be obtained with different tests applied to the same molecules. At least two different methods should be used to evaluate the antioxidant activity of a molecule or a food extract. " Second, lipophilicity is an important factor to consider in testing the antioxidant activities... 

Experimental evidence in humans is based upon intervention studies with diets enriched in carotenoids or carotenoid-contaiifing foods. Oxidative stress biomarkers are measured in plasma or urine. The inhibition of low density lipoprotein (LDL) oxidation has been posmlated as one mechanism by which antioxidants may prevent the development of atherosclerosis. Since carotenoids are transported mainly via LDL in blood, testing the susceptibility of carotenoid-loaded LDL to oxidation is a common method of evaluating the antioxidant activities of carotenoids in vivo. This type of smdy is more precisely of the ex vivo type because LDLs are extracted from plasma in order to be tested in vitro for oxidative sensitivity after the subjects are given a special diet. 

This method is relatively easy to use for anhydrous systems, but not for emulsions, foods, or biological media where the presence of water is detrimental. The method has been applied for determining antioxidant activity of both individual natural polyphenols and vegetable extracts. Methods based on this one have been used to evaluate the peroxide value in walnuts (Wilson-Kakashita and others 1995), mango seeds (Joseph 1995), almonds (Uthman and others 1998), and coconut cream powder (Yusof and others 2007). 

The ORAC assay proposed by Ou and others (2001) is limited to hydrophilic antioxidants because of the aqueous environment of the assay. However, lipophilic antioxidants play a critical role in biological defense systems. Huang and others (2002) expanded the assay to the lipidic fraction by introducing a randomly methylated 13-cyclodextrin (RMCD) as a water-solubility enhancer for lipophilic antioxidants. Various kinds of foods, including fruit juices and drinks, fruits, vegetables, nuts, and dried fruits, have been evaluated with this method (Zhou and Yu 2006 Wu and others 2004 Kevers and others 2007 Wang and Ballington 2007 Almeida and others 2008 Mullen and others 2007). 

Many methods are available for determining food antioxidant capacity, which is an important topic in food and nutrition research. However, there is a great need to standardize these methods because the frequent lack of an actual substrate in the procedure, the system composition, and the method of inducing oxidation could limit their accuracy. In fact, antioxidant activities in complex systems cannot be evaluated satisfactorily using a single test, and several test procedures may be required. The search for more specific assays that can be more directly related to oxidative deterioration of foods and biological systems should be the objective of future investigations. 

Cervellati R, Renzulli C, Guerra MC and Speroni E. 2002. Evaluation of antioxidant activity of some natural polyphenolic compounds using the Briggs-Rauscher reaction method. J Agric Food Chem 50(26) 7504-7509. 

Frankel EN. 1993. In search of better methods to evaluate natural antioxidants and oxidative stability in food lipids. Trends Food Sci Technol 4(7) 220-225. 

Stewart RJ, Askew EW, McDonald CM, Metos J, Jackson WD, Balon TW and Prior RL. 2002. Antioxidant status of young children response to an antioxidant supplement. J Am Diet Assoc 102(11) 1652—1657. Stratil P, Klejdus B and Kuban V. 2006. Determination of total content of phenolic compounds and their antioxidant activity in vegetables evaluation of spectrophotometric methods. J Agric Food Chem... 

Antioxidant capacity can be measured by several techniques, each of which has its own limitations. Antioxidant capacity of fruit juices and purees was evaluated by the DPPH method (which measures the radical-scavenging activity against a nonphysio-logical free radical), and treatment of these products with PEF or HHP resulted in losses... 

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