Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method. This overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. From evaluation of data presented at the First International Congress on Antioxidant Methods in 2004 and in the literature, as well as consideration of potential end uses of antioxidants, it is proposed that procedures and applications for three assays be considered for standardization: the oxygen radical absorbance capacity (ORAC) assay, the Folin-Ciocalteu method, and possibly the Trolox equivalent antioxidant capacity (TEAC) assay. ORAC represent a hydrogen atom transfer (HAT) reaction mechanism, which is most relevant to human biology. The Folin-Ciocalteu method is an electron transfer (ET) based assay and gives reducing capacity, which has normally been expressed as phenolic contents. The TEAC assay represents a second ET-based method. Other assays may need to be considered in the future as more is learned about some of the other radical sources and their importance to human biology.

https://faculty.missouri.edu/~glaserr/3700s14/Antioxidant-Capacity_jf0502698.pdf

Standardized Methods for the Determination of Antioxidant Capacity and Phenolics in Foods and Dietary Supplements

Polyphenols constitute one of the most numerous and ubiquitous groups of plant metabolites and are an integral part of both human and animal diets. Ranging from simple phenolic molecules to highly polymerized compounds with molecular weights of greater than 30,000 Da, the occurrence of this complex group of substances in plant foods is extremely variable. Polyphenols traditionally have been considered antinutrients by animal nutritionists, because of the adverse effect of tannins, one type of polyphenol, on protein digestibility. However, recent interest in food phenolics has increased greatly, owing to their antioxidant capacity (free radical scavenging and metal chelating activities) and their possible beneficial implications in human health, such as in the treatment and prevention of cancer, cardiovascular disease, and other pathologies. Much of the literature refers to a single group of plant phenolics, the flavonoids. This review offers an overview of the nutritional effects of the main groups of polyphenolic compounds, including their metabolism, effects on nutrient bioavailability, and antioxidant activity, as well as a brief description of the chemistry of polyphenols and their occurrence in plant foods.

Polyphenols: Chemistry, Dietary Sources, Metabolism, and Nutritional Significance

Publisher Summary This chapter discusses ferric reducing/antioxidant power (FRAP) assay. The ferric reducing/antioxidant power (FRAP) assay is a recently developed, direct test of “total antioxidant power.” The FRAP assay is robust, sensitive, simple, and speedy and facilitates experimental and clinical studies investigating the relationship among antioxidant status, dietary habits, and risk of disease. Measurement of the total antioxidant power of fresh biological fluids—such as blood plasma—can be measured directly; the antioxidant content of various dietary agents can be measured objectively and reproducibly and their potential for improving the antioxidant status of the body investigated and compared. The FRAP assay is also sensitive and analytically precise enough to be used in assessing the bioavailability of antioxidants in dietary agents to help monitor longitudinal changes in antioxidant status associated with an increased intake of dietary antioxidants and to investigate the effects of disease on antioxidant status.

Ferric reducing/antioxidant power assay: direct measure of total antioxidant activity of biological fluids and modified version for simultaneous measurement of total antioxidant power and ascorbic acid concentration

Phenolic compounds in plants and agri-industrial by-products: Antioxidant activity, occurrence, and potential uses

Molyneux, P. The use of the stable free radical diphenylpicrylhydrazyl (DPPH) for estimating antioxidant activity

https://rdo.psu.ac.th/sjstweb/journal/26-2/07-DPPH.pdf

The use of the stable free radical diphenylpicrylhydrazyl (dpph) for estimating antioxidant activity

The kinetic behaviour of polyphenols common in fruits as free radical scavengers was studied using 2,2-diphenyl-1-picrylhydrazyl (DPPH.). After addition of different standard concentrations to DPPH. (0.025 g litre-1), the percentage of remaining DPPH. was determined at different times from the absorbances at 515 nm. The percentage remaining DPPH. against reaction time followed a multiplicative model equation: In [DPPH.REM] = b 1n t + 1n a. The slopes of these equations may be useful parameters to define the antioxidant capacity. The steeper the slope, the lower the amount of antioxidant necessary to decrease by 50% the initial DPPH. concentration (EC50). This parameter, EC50, is widely used to measure antioxidant power, but it does not takes into account the reaction time. Time needed to reach the steady state to the concentration corresponding at EC50 (T(EC50)) was calculated, and antiradical efficiency (AE) was proposed as a new parameter to characterise the antioxidant compounds where AE = 1/EC50 T(EC50). It was shown that AE is more discriminatory than EC50. AE values are more useful because they also take into account the reaction time. The results have shown that the order of the AE (x 10(-3)) in the compounds tested was: ascorbic acid (11.44) > caffeic acid (2.75) greater than or equal to gallic acid (2.62) > tannic acid (0.57) greater than or equal to DL-alpha-tocopherol (0.52) > rutin (0.21) greater than or equal to quercetin (0.19) > ferulic acid (0.12) greater than or equal to 3-tert-butyl-4-hydroxyanisole, BHA (0.10) > resveratrol (0.05).

A procedure to measure the antiradical efficiency of polyphenols

The effect of drying temperature (60, 100, and 140 °C) on the polyphenols' content and antioxidant activity of red grape pomace peels was studied. Freeze-dried samples were used as reference. Differences on the CIE-LAB color, total extractable polyphenols, condensed tannins, UV−vis spectra, and antioxidant activity were evaluated. When drying temperature was 100 and 140 °C, a significant reduction in both total extractable polyphenols (18.6 and 32.6%) and condensed tannins (11.1 and 16.6%) was observed, as well as a decrease of 28 and 50% in the antioxidant activity of the samples, respectively. Hue angle and total color difference in the sample dried at 140 °C were significantly higher than in the freeze-dried reference material. A red color loss at 140 °C was also confirmed by lower absorbance values in the spectra at 525 nm. Drying at 60 °C did not significantly affect the sample characteristics evaluated. Keywords: Wine byproducts; grape pomace peels; antioxidant activity; drying temperature

Effect of drying temperature on the stability of polyphenols and antioxidant activity of red grape pomace peels

Free radical scavenging capacity and inhibition of lipid oxidation of wines, grape juices and related polyphenolic constituents

In this study, isolation and characterization of mango peel dietary fibre were investigated. Fresh mango peels, obtained as a byproduct of syrup production, were successively wet-milled, washed with water and dried. A peel particle size of 15 mm in wet milling and a washing time of 5 min were found to remove soluble sugars and to increase total polyphenols and soluble dietary fibre content. Mango peel dietary fibre contained high amounts of total extractable polyphenols (70 g/kg) and soluble dietary fibre (281 g/kg) and had a high water-holding capacity (11·4 g/g dry matter). These characteristics indicated that mango peel is a good source of tropical fruit fibre.

Mango peels as a new tropical fibre: preparation and characterization

Free radical scavenging capacity of the extracts from red and white grape pomace peels (RGPP, WGPP) and as a reference for two commonly used antioxidants (BHA (synthetic) and dl-α-tocopherol (natural) heated at processing temperatures (80, 100, and 120 °C) was evaluated using the 2,2-diphenyl-1-picrylhidrazyl (DPPH•) reagent. Kinetic behavior of the sample extracts did not change when they were heated, following a general multiplicative model in which remaining DPPH• was more affected by temperature than the time needed to reach the steady state. The reduction of this property in the sample extracts heated at 120 °C as compared to those at 20 °C followed an increasing order:  BHA (15.3%) < WGPP (22.9%) < RGPP (28.3%) < dl-α-tocopherol (69.8%). Color losses were also measured by a tristimulus colorimeter HunterLab and two parameters were used to express the sample extract color:  hue angle (tan b*/a*)-1 and a*/b* ratio. The higher red color losses in RGPP extracts (12.9 times in hue angle) as compared to t...

José A. Larrauri

Papers

A procedure to measure the antiradical efficiency of polyphenols

Effect of drying temperature on the stability of polyphenols and antioxidant activity of red grape pomace peels

Free radical scavenging capacity and inhibition of lipid oxidation of wines, grape juices and related polyphenolic constituents

Mango peels as a new tropical fibre: preparation and characterization

Effect of temperature on the free radical scavenging capacity of extracts from red and white grape pomace peels