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Cover
Title Page
List of contributors
1 Nomenclature and general classification of antioxidant activity/capacity assays
1. 1.1 Introduction
2. 1.2 Nomenclature of antioxidant activity/capacity assays
3. 1.3 Classification of antioxidant activity/capacity assays
4. 1.4 Conclusions
5. References
2 Assays based on competitive measurement of the scavenging ability of reactive oxygen/nitrogen species
1. 2.1 Introduction
2. 2.2 Kinetics is more important than thermodynamics when it comes to scavenging ROS
3. 2.3 Peroxyl radical scavenging capacity assay based on inhibition of lipid autoxidation
4. 2.4 Application of molecular probes for quantification of antioxidant capacity in scavenging specific ROS/RNS
5. 2.5 Conclusion: a unified approach for measuring antioxidant capacity against different ROS?
6. Acknowledgment
7. References
3 Evaluation of the antioxidant capacity of food samples: a chemical examination of the oxygen radical absorbance capacity assay
1. 3.1 Introduction
2. 3.2 Chemical assays to evaluate the antioxidant capacity of food samples
3. 3.3 Chemical examination of the ORAC assay: advantages and drawbacks
4. 3.4 Future perspectives to improve the antioxidant capacity evaluation of food samples
5. 3.5 Conclusions
6. Acknowledgments
7. References
4 Electron transfer‐based antioxidant capacity assays and the cupric ion reducing antioxidant capacity (CUPRAC) assay
1. 4.1 Introduction
2. 4.2 ET‐based TAC assays
3. 4.3 CUPRAC assay of antioxidant capacity measurement
4. References
5 The ferric reducing/antioxidant power (FRAP) assay for non‐enzymatic antioxidant capacity: concepts, procedures, limitations and applications
1. 5.1 Introduction: concepts and context
2. 5.2 The ferric reducing/antioxidant power (FRAP) assay: a brief overview
3. 5.3 Working concepts, what results represent, potential interferences, and limitations
4. 5.4 Method outline and detailed procedures for manual, semi‐automated, and fully automated modes
5. 5.5 Technical tips for the FRAP assay
6. 5.6 Issues of standardization (calibration) and how results are expressed
7. 5.7 Issues of sample handling, storage, and extraction
8. 5.8 Modifications to the FRAP assay
9. 5.9 Illustrative applications
10. 5.10 Cautions and concluding remarks
11. Acknowledgments
12. References
13. Further reading
6 Folin–Ciocalteu method for the measurement of total phenolic content and antioxidant capacity
1. 6.1 Introduction
2. 6.2 Is the Folin–Ciocalteu method an antioxidant assay?
3. 6.3 Folin–Ciocalteu assay to quantify phenolic compounds
4. 6.4 Folin–Ciocalteu index in wines
5. 6.5 Improving the method: more sustainability, less time, and lower cost
6. 6.6 Beneficial effects of polyphenols measured by the Folin–Ciocalteu assay in human biological samples: a biomarker of polyphenol intake
7. References
7 ABTS/TEAC (2,2’‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid)/Trolox®‐Equivalent Antioxidant Capacity) radical scavenging mixed‐mode assay
1. 7.1 Introduction
2. 7.2 Use of ABTS as a sensor of antioxidant activity: the TEAC assay
3. 7.3 Advantages and disadvantages
4. 7.4 TEAC assay in hyphenated and high‐throughput techniques
5. 7.5 TEAC in pure compounds
6. 7.6 TEAC in foods
7. 7.7 Future perspectives
8. References
8 DPPH (2,2‐di(4‐tert‐octylphenyl)‐1‐picrylhydrazyl) radical scavenging mixed‐mode colorimetric assay(s)
1. 8.1 Overview
2. 8.2 Characteristics of the DPPH radical
3. 8.3 The concept behind the development of the DPPH colorimetric assay (Blois 1958)
4. 8.4 How can antioxidants scavenge the DPPH?
5. 8.5 The evolution of ideas on the underlying mechanism
6. 8.6 The DPPH colorimetric assay(s)
7. 8.7 Toward the standardization of a DPPH assay to address structure–activity relationship issues
8. 8.8 Toward the establishment of a DPPH assay for regulatory and market needs
9. 8.9 Concluding remarks – À la rechèrche du temps perdu
10. References
9 Biomarkers of oxidative stress and cellular‐based assays of indirect antioxidant measurement
1. 9.1 Introduction
2. 9.2 Oxidative stress
3. 9.3 Biomarkers of oxidative stress
4. 9.4 Cell‐based assays of indirect antioxidant measurement
5. 9.5 Conclusion
6. References
10 Nanotechnology‐enabled approaches for the detection of antioxidants by spectroscopic and electrochemical methods
1. 10.1 Introduction
2. 10.2 Spectroscopic nano‐based approaches for antioxidant detection
3. 10.3 Electrochemical detection
4. 10.4 Conclusions and future research needs
5. Acknowledgments
6. References
11 Novel methods of antioxidant assay combining various principles
1. 11.1 Introduction
2. 11.2 Lipid peroxidation and formation of primary and secondary oxidation products
3. 11.3 Use of gas chromatography for antioxidant assays
4. 11.4 Novel gas chromatographic antioxidant assays
5. 11.5 Conclusion
6. References
12 Physico‐chemical principles of antioxidant action, including solvent and matrix dependence and interfacial phenomena
1. 12.1 Introduction
2. 12.2 Mechanism and kinetics of peroxidation
3. 12.3 Initiation of lipid peroxidation chains
4. 12.4 Antioxidants
5. 12.5 How to recognize a good chain‐breaking antioxidant
6. 12.6 Determination of reactivity of a CBA towards peroxyl radicals
7. 12.7 Basic mechanisms of antioxidant action
8. 12.8 Interfacial phenomena – studies in heterogeneous lipid systems
9. 12.9 Effect of temperature
10. Acknowledgments
11. References
13 Evaluation of antioxidant activity/capacity measurement methods for food products
1. 13.1 Introduction
2. 13.2 Antioxidant assay selection for different food products
3. 13.3 General conclusions and future perspectives
4. References
14 Antioxidants in oxidation control
1. 14.1 Introduction
2. 14.2 Oxidation
3. 14.3 Antioxidants
4. 14.4 Synthetic antioxidants
5. 14.5 Natural antioxidants
6. 14.6 Tocols
7. 14.7 Ascorbic acid
8. 14.8 Carotenoids
9. 14.9 Polyphenols
10. 14.10 Bioavailability of phenolic antioxidants
11. 14.11 Structural and other modification of phenolic antioxidants
12. 14.12 Protein‐derived antioxidants
13. 14.13 Phospholipids
14. 14.14 Other antioxidants
15. References
15 Kinetic matching approach for rapid assessment of endpoint antioxidant capacity
1. 15.1 Introduction
2. 15.2 Kinetic matching strategy
3. 15.3 Expression of results as common standard
4. 15.4 Application to samples
5. 15.5 Conclusion
6. Acknowledgments
7. References
Index
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List of Tables

Chapter 01
1. Table 1.1 Nomenclature of antioxidant activity/capacity assays.
2. Table 1.2 General classifications of antioxidant activity/capacity assays
Chapter 02
1. Table 2.1 Antioxidant capacity of phenolic compounds in a microemulsion system (ORAC_E).
2. Table 2.2 Superoxide scavenging activity of phenolic compounds (SORAC values are expressed as epicatechin equivalence which has SORAC value of 14,417 units of SOD equivalent per mole, n > 3).
3. Table 2.3 NO₂ scavenging capacity of phenolic compounds.
4. Table 2.4 Singlet oxygen scavenging activity of selected compounds.
5. Table 2.5 HClO scavenging capacity of biological antioxidants.
Chapter 03
1. Table 3.1 Main characteristics and shortcomings of the in vitro assays to evaluate antioxidant activity.
Chapter 05
1. Table 5.1 Preparation of working aqueous ascorbic acid standards from a freshly prepared stock standard.
2. Table 5.2 Illustrative applications of the FRAP assay for NEAC; for specific relevant sources, the reader is referred to the reference list.
Chapter 06
1. Table 6.1 Possible interfering substances in urine that may react with the Folin–Ciocalteu reagent.
2. Table 6.2 Folin–Ciocalteu assay after the clean‐up procdure.
Chapter 07
1. Table 7.1 Proposed mechanisms for the reduction of ABTS^•+ by antioxidant.
2. Table 7.2 Trolox Equivalent Antioxidant Capacity (TEAC) values of some relevant pure compounds, using the ABTS^•+ chromogen.
3. Table 7.3 Trolox Equivalent Antioxidant Capacity (TEAC) values of some beverages, using the ABTS^•+ chromogen.
4. Table 7.4 Trolox Equivalent Antioxidant Capacity (TEAC) values of some fruits, using the ABTS^•+ chromogen.
5. Table 7.5 Trolox Equivalent Antioxidant Capacity (TEAC) values of some vegetables, using the ABTS^•+ chromogen.
6. Table 7.6 Trolox Equivalent Antioxidant Capacity (TEAC) values of some meats, using the ABTS^•+ chromogen.
Chapter 08
1. Table 8.1 Commercial sources for DPPH^• (CAS number: 1898‐66‐4) and relevant information provided.
2. Table 8.2 Solvent effect on DPPH^• scavenging by phenolic antioxidants.
3. Table 8.3 Observed rate constants,^a^,^b k₁ (M⁻¹ s⁻¹), and stoichiometric factors,^c n, for the reaction of DPPH^• with selected phenolic compounds in methanol and ethanol at 25 °C.
Chapter 09
1. Table 9.1 Nomenclature of common reactive species.
2. Table 9.2 Major oxidative stress biomarkers and methods of detection.
Chapter 10
1. Table 10.1 Summary of analytical characteristics of reviewed studies that utilize nanotechnological tools for antioxidant assessment using spectroscopic and electrochemical procedures.
Chapter 11
1. Table 11.1 Typical secondary oxidation products from various lipids oxidized by different methods.
2. Table 11.2 Antioxidant studies using GC/MA assay.
3. Table 11.3 Antioxidant activity of various plants and their major components evaluated by aldehyde/carboxylic acid assay.
Chapter 12
1. Table 12.1 Examples of structures of lipid‐soluble and water‐soluble azo‐initiators, the kinetic parameters of their decomposition, and structures of primary and secondary (peroxyl) radicals formed.
2. Table 12.2 The rate constants for the reactions of peroxyl radicals with six phenolic CBAs (structures presented in the text) in homogeneous solution and in dilinoleoylphosphatidylcholine (DLPC) membranes.
Chapter 13
1. Table 13.1 Most widely used antioxidant activity/capacity measurement assays.
2. Table 13.2 Studies comparing different antioxidant activity/capacity assays with various food products.
Chapter 14
1. Table 14.1 Major food sources and contents (mg/100 g) of flavonoids, phenolic acids, lignans, and stillbenes.
2. Table 14.2 Phenolic compounds identified from fruits, vegetables, cereals, legumes, and oilseeds.
3. Table 14.3 Food‐derived protein hydrolysates with antioxidant activities.
Chapter 15
1. Table 15.1 Kinetic matching standards selected for different samples upon application of different chemistries for evaluation of total antioxidant capacity.

List of Illustrations

Chapter 02
1. Figure 2.1 (Left) Emulsion (milky tube) and microemulsion (transparent tube) containing methyl linoleate immediately after preparation. (Right) Same tubes after 2 hours of preparation. Phase separation occurs for emulsion but not for microemulsion, which is thermodynamically stable.
2. Figure 2.2 (Top) Kinetic curves of different concentrations of Trolox showing protection of ML from oxidation in microemulsion. Concentrations of Trolox from curves 1–6 are 0, 5.2, 10.4, 20.8, 41.6, and 83.3 (μM) respectively. The reaction was carried out in a microreactor fitted with an oxygen electron for monitoring of the oxidation progress at 37 °C. Reaction volume was 0.60 mL and AAPH concentration was 17 µg/mL. (Bottom) Standard curves obtained by microplate (y = 1.7468× –2.0176, o, solid line, n = 3) and Clark oxygen electrode (y = 1.6644× –1.1508, X, dotted line, n = 3). The overlapping curves demonstrate that the high‐throughput microplate method is comparable with the low‐throughput oxygen electrode approach.
3. Figure 2.3 Reaction products of HE with superoxide anion in the presence or absence of myricetin or quercetin.
4. Figure 2.4 Linear plots of relative initial rates versus concentration of different antioxidants. EC, epicatechin; ECG epicatechin gallate; EGC, epigallocatechin; EGCG, epigallocatechin gallate; EAC, epiafzelechin.
5. Figure 2.5 Plausible reaction mechanism and products (observed) of the reaction between NO₂ with EC and gallic acid.
Chapter 03
1. Figure 3.1 (a) The basic structure of PC. Four groups are presented: benzoic and cinnamic acids, flavonoids, and stilbenes. (b) Chemical structures of six subgroups of flavonoids.
2. Figure 3.2 Possible reactions involved during the antioxidant activity of polyphenols in cell cultures. FR, free radicals; GSH, glutathione; PC‐OH, phenolic compounds.
3. Figure 3.3 Kinetic profiles of the luminescence of a solution of luminol and AAPH in the absence and presence of a tea bag extract of yerba mate. (a) In the presence of aliquots of yerba mate, 5 μL (curve a), 7.5 μL (curve b), and 10 μL (curve c). The original extract was diluted 100 times. (b) In the presence of aliquots of yerba mate, 1 μL (curve a), 5 μL (curve b), and 10 μL (curve c). The original extract was diluted 1000 times.
4. Figure 3.4 (a) Chemical structure of FL. (b) Kinetic profiles of FL consumption mediated by AAPH‐derived free radicals. Curve a: FL 70 nM + AAPH 10 mM. Curves b, c, d, and e represent the kinetic profiles obtained with increasing Trolox concentrations; 2.5, 5.0, 7.5, and 10 μM, respectively.
5. Figure 3.5 (a) Chemical structure of PGR. (b) Kinetic profiles of PGR consumption mediated by AAPH‐derived free radicals. Curve a: PGR 5 μM + AAPH 10 mM. Curves b and c represent the kinetic profiles obtained with increasing Trolox concentrations; 50 and 100 μM, respectively.
6. Figure 3.6 Dependence of the initial consumption rate (Ri) of PGR () and FL () with their initial concentration. Consumption of PGR and FL was followed by visible spectroscopy (at 540 nm), and fluorescence (exc. = 493 nm and em. = 515 nm), respectively. Solutions were incubated in phosphate buffer (75 mM, pH 7.4) at 37 °C in the presence of AAPH at 10 mM concentration.
Chapter 04
1. Figure 4.1 Reaction scheme for the CUPRAC antioxidant capacity assay (liberated protons are buffered in relatively concentrated ammonium acetate solution).
Chapter 05
1. Figure 5.1 Concept of oxidant/antioxidant balance as a disruption in antioxidant balance in the direction of oxidation caused by an increase in oxidant load and/or a decrease in antioxidant defence.
2. Figure 5.2 Reaction kinetics of different test samples in the FRAP assay (under standard conditions of 37 °C and pH 3.6). Samples were: A = Fe²⁺ 1 mM; B = plasma (neat); C = tea 1% w/v; D = ascorbic acid 250 μM; E = α‐tocopherol 200 μM; F = uric acid 200 μM; G = albumin 40 g/L; H = GSH 1 mM; I = cysteine 1 mM; J = glucose 5 mM. All solutions were aqueous except for α‐tocopherol, which was in ethanol. Absorbance readings were taken immediately before sample addition, 0.5 sec after sample addition, and at 15 sec intervals thereafter up to 4 min post sample/reagent mixing.
3. Figure 5.3 Effect of different pH of reaction on FRAP assay results. Test samples were human plasma (triangles), tea (diamonds), ascorbic acid (squares), uric acid (circles). FRAP values were calculated with reference to a 1000 μM Fe²⁺ standard run under the same conditions as these test samples.
4. Figure 5.4 Effect of temperature on results in the FRAP assay. Results (as FRAP values) of the same samples of human plasma (triangles), tea (diamonds), ascorbic acid (squares) and uric acid (circles) tested at 37 °C, 25 °C and 20 °C, with results obtained using a 1000 µmol/L Fe²⁺ standard tested in parallel under the same conditions. Reaction time of 4 min was used for all samples at all temperatures.
5. Figure 5.5 Typical FRAP assay dose–response lines for Fe²⁺ (circles) and ascorbic acid (squares).
6. Figure 5.6 Stability of the reaction mixture at up to 10.5 min post sample/reagent mixing (under standard test conditions of 37 °C and pH 3.6) for Fe²⁺ (open diamonds), human plasma (triangles), ascorbic acid (squares), uric acid (circles) and tea (filled diamonds).
Chapter 06
1. Figure 6.1 Comparison of results obtained with the F–C method in red and white wines from the island of Mallorca with those of two other antioxidant capacity assays.
2. Figure 6.2 Standard gallic acid curve in synthetic urine.
3. Figure 6.3 Content of total phenol in mg GAE/g creatinine excreted in morning urine.
Chapter 07
1. Figure 7.1 (a) Absorption spectrum of the ABTS and its radical cation (ABTS^•+). (b) Chemical structures of ABTS, ABTS^•+ and its dication (ABTS²⁺).
2. Figure 7.2 Strategies for antioxidant activity determination (see text).
3. Figure 7.3 Hydrophilic, lipophilic, and total antioxidant activities of tomato and Spanish gazpacho soups. The relative contribution (%) of ascorbic acid, lycopene, and β‐carotene is shown.
Chapter 08
1. Figure 8.1 Optimized DPPH^• structure (a) and calculated spin distribution (b) at the B3LYP/6‐31G(d) level in the gas phase (T = 298 K) on the basis of internal coordinates.
2. Figure 8.2 Reaction stoichiometry between DPPH^• and (a) ascorbic acid (2:1), (b) cystenine (1:1); (c) hydroquinone (2:1) according to Blois (1958); DPPH‐H: the respective hydrazine.
3. Figure 8.3 Reaction of phenols (AH) with DPPH^•; the solvent is polar.
4. Figure 8.4 Proposed mechanism for DPPH^• scavenging by curcumin in methanol or ethanol (I–V) and in dioxane and ethylacetate (V).
5. Figure 8.5 Proposed formation of the reaction products of quercetin and DPPH^• in acetonitrile (a) and methanol (b).
6. Figure 8.6 Proposed formation of the reaction products of quercetin and DPPH^• in the presence of aqueous methanol.
7. Figure 8.7 Basic steps of the proposed protocol for the evaluation of antioxidant activity evaluation by Brand‐Williams et al. (1995).
8. Figure 8.8 Outline of the basic steps for a DPPH^• protocol suitable for structure– antioxidant activity studies extracted from proposals made by Apak et al. (2013).
9. Figure 8.9 Stoichiometric coefficients (a) and rates of initial reaction with DPPH^• (b) at various concentrations of phenols.
10. Figure 8.10 The influence of dissolution solvent type (a) and solvent volume (b) in the measuring system on the kinetics of DPPH^•/BHT reaction carried out during 60 min at low concentration of BHT.
11. Figure 8.11 Basic steps for the establishment of a DPPH^• index for regulatory and market needs according to the protocol of Plank et al. (2012).
12. Figure 8.12 Schematic representation of the basic steps of the direct QUENCHER procedure.
Chapter 09
1. Figure 9.1 Pathways and potential usages of selected oxidative stress biomarkers. Advanced glycation endproducts (AGEs) derive from glycoxidation and lipoxidation of proteins and amino acids. The oxidized bases 8‐hydroxyguanosine (8‐OHG) and 8‐hydroxy‐2‐deoxyguanosine (8‐OHdG) are the most common oxidized bases, thus they are used as markers of RNA and DNA oxidation. MDA is an aldehyde derived from lipid peroxidation in vivo, as an arachidonate byproduct. 4‐Hydroxynonenal (4‐HNE) is an α,β‐unsaturated aldehyde as a peroxidation product of polyunsaturated fatty acids. Lipid hydroperoxides (LOOHs) are utilized as a marker of peroxidative damage of membrane lipids. As biomarkers of oxidative damage to lipids, thiobarbituric acid‐reactive substances (TBARS) can be measured in plasma, serum, erythrocytes, and leukocytes. Non‐enzymatic antioxidants include vitamins A, C and E, carotenoids, flavonoids, glutathione, uric acid and other antioxidants minerals such as copper, zinc, iron, ferritin, manganese, and selenium. Antioxidant enzymes include superoxide dismutase (SOD), catalase (CAT), xanthine oxidase (XO), and glutathione‐related enzymes (GPx, GR, GST, and thioredoxin reductase) and heme oxygenase.
2. Figure 9.2 Different mechanisms of antioxidant action: (1) inhibition of oxidant enzymes, (2) interaction with redox signaling pathways, (3) direct reaction with ROS/RNS. Enzymes producing ROS/RNS: NOS (nitric oxide synthase), NOx (NADPH oxidase), COX (cyclooxygenase), MPO (myeloperoxidase). Antioxidant enzymes: CAT (catalase), SOD (superoxide dismutase), Prx (peroxiredoxin), GPx (glutathione peroxidase), Trx (thioredoxin), TR (thioredoxin reductase), GR (glutathione reductase).
3. Figure 9.3 Schematic depiction of Keap1‐Nrf2‐ARE and NF‐κB‐IκB pathways activated by ROS. Increased ROS formation or exposure to electrophilic metabolites would modify or oxidize cysteine residues in Keap1, causing the dissociation of Nrf‐2/Keap1 complex. The corresponding accumulation of Nrf‐2 to reach the nucleus and its binding to the ARE result in increased transcription of genes, triggering increased expression of antioxidant enzymes. In the cytoplasm, NF‐κB is kept inactive by binding with IκB (inhibitor of NF‐κB) proteins. During exposure to oxidants, IκB proteins are rapidly degraded, releasing NF‐κB protein to the nucleus where NF‐κB could bind to certain DNA sequences, and activate the expression of specific proinflammatory and antiapoptotic genes.
4. Figure 9.4 Schematic depiction of the cellular antioxidant activity assay. Cells are loaded with antioxidant compounds and the fluorescence probe 2′,7′‐dichlorofluorescin diacetate (DCFH‐DA). The antioxidants could bind to the cell membrane and/or pass through the membrane to enter the cell. DCFH‐DA diffused into the cell is hydrolyzed by cellular esterases to form the polar molecule 2′,7′‐dichlorofluorescin (DCFH), which is trapped in the cell. 2,2′‐azobis (2‐amidinopropane) dihydrochloride (AAPH), which is able to diffuse into cells and attack the cell membrane to produce peroxyl radicals, will also generate more peroxyl radicals within cells and oxidize the intracellular DCFH to form the fluorescent dichlorofluorescein (DCF). Antioxidants could prevent the oxidation of membrane lipids and DCFH, react with ROO^• and inhibit the formation of ROS, and diminish the production of the fluorescent DCF.
Chapter 10
1. Figure 10.1 Summary of the varying NPs used to detect antioxidants.
2. Figure 10.2 Overview of colorimetric and electrochemical detection schemes based on NPs.
3. Figure 10.3 (a) AuNP spectra obtained from 10 different extra virgin olive oil (EVOO) extracts at a concentration of 140 mg mL⁻¹. The inset photograph shows a blank solution and the AuNPs formed with a sample (#5). (b) Sigmoidal curves obtained by increasing the amount of extract of the EVOO samples by 2, 4, 6, 8.
4. Figure 10.4 Schematic illustration of the fabrication of gold nanoparticles (GNPs) and their application in antioxidant capacity assay using silica (SiO₂) functionalized with (3‐aminopropyl)triethoxysilane (APTES) and GNPs to generate gold nanospheres (GNS) in the presence of antioxidants.
5. Figure 10.5 Ceria nanoparticle‐based assay for rapid detection of food antioxidants.
6. Figure 10.6 Schematic representation of the process for constructing the electrochemical sensing platform using AuNPs and graphene oxide (GO) on glassy carbon electrode (GCE).
7. Figure 10.7 The illustration of the β‐CD‐Au@PTCA‐SWCNHs nanohybrids using an electrochemical strategy for simultaneous detection of myricetin and rutin.
8. Figure 10.8 Schematic illustration of enlargement of Au nanoparticles by flavonoids at cysteamine modified electrode.
9. Figure 10.9 Schematic of the electrochemical detection mechanism of a model antioxidant, gallic acid, using biomimetic ceria NPs as an oxidation catalyst at the surface of screen‐printed electrodes and example of amperometric readings of ascorbic acid in the presence (Gray) and absence (black) of ceria NPs. In the absence of NPs, no electrochemical response is observed.
Chapter 11
1. Figure 11.1 Proposed formation pathways of secondary lipid peroxidation products.
2. Figure 11.2 Reaction scheme of N‐methypyrazle from MA and 1‐methylhydrazine.
3. Figure 11.3 A typical gas chromatogram of oxidized arachidonic acid solution after 1‐methylhydrazine treatment taken by a 30 m × 0.25 mm i.d. (d_f = 1 mm) DBWAX fused silica capillary column.
4. Figure 11.4 Oxidative conversion of aldehyde to carboxylic acid.
5. Figure 11.5 Typical results of antioxidant evaluation on licorice root extract obtained by the aldehyde/carboxylic acid assay.
Chapter 12
1. Scheme 12.1 Autoxidation of lipid initiated by primary radicals (initiators, peroxides, hydroperoxides).
2. Scheme 12.2 Thermal decomposition of ABAP in aerated solution.
3. Scheme 12.3 Mechanism of decomposition of SOTS‐1 in aerated water, pH 7, at 37 °C (Konya et al. 2000).
4. Scheme 12.4 Mechanism of photo‐initiation with benzophenone as photosensitizer.
5. Figure 12.1 Idealized kinetic traces of peroxidation process – plots of oxygen uptake by the system, Δ[O₂], or of concentration of hydroperoxides, [LOOH], in the oxidized sample versus time of oxidation. The plotted curves are obtained typically during the process of spontaneous (uninhibited) peroxidation proceeding at rate R_ox (a), inhibited peroxidation with an induction period (lag phase, τ_ind) distinguished as a separate kinetic stage: process proceeds at rate R_inh during τ_ind and at rate R_ox2 after the end of τ_ind (b) and retarded peroxidation proceeding at rate R_ret (c).
6. Scheme 12.5 Antioxidant action of a chain‐breaking antioxidant (CBA‐H). CBA‐H traps peroxyl radical and is simultaneously oxidized to a radical form, CBA^•. The reaction of CBA‐H with LOO^• can proceed by different pathways (mechanisms), not depicted in this scheme. The scheme also does not include consecutive reactions of CBA^•.
7. Scheme 12.6 Primary products of autoxidation of linoleic acid (or methyl linoleate) in the presence of chain‐breaking antioxidant (CBA).
8. Scheme 12.7 Idea of competitive methods and examples of structures of compounds applied as probes: fluorescein, pyrogallol red, and luminol.
9. Figure 12.2 (a) Schematic of a single chamber with a Clark type oxygen probe immersed in a plunger. Based on the YSI 5300A Biological Oxygen Monitor System – Operations Manual (courtesy of YSI, Inc.). (b) Block diagram of the apparatus used in the pressure sensor method. M, membrane; PC, computer; PT, pressure transducer; R, reference flask; S, sample flask; STR, strip chart recorder; TB, thermostatted bath; UPC, UPC converter card; V, three‐way Teflon valve.
10. Scheme 12.8 Comparison of two mechanisms of reaction between a phenol (PhOH) and a model radical Y^•: hydrogen atom transfer (HAT) and sequential proton‐loss electron transfer (SPLET, red frame). HAT exhibits large kinetic solvent effects in HBA solvents because PhOH that is hydrogen bonded to a solvent S does not react with a radical Y^•.
11. Scheme 12.9 Remote kinetic solvent effect for 1,4‐hydroquinone.
12. Scheme 12.10 Reaction of alkoxyl radicals with diphenylmethane (a) and diphenylamine (b).
13. Scheme 12.11 Mechanism of PCET for PhOH/PhO^• reaction (Mayer et al. 2002). The proton is transferred from its two bonding electrons to the lone pair of PhO^• and, simultaneously, the electron moves from the 2p lone pair on PhOH to the singly occupied molecular orbital (SOMO) of PhO^•.
14. Scheme 12.12 Reaction of a phenolic CBA with peroxyl radical catalyzed by acetic acid.
15. Figure 12.3 Model lipid systems for kinetic studies. Lipids can be dispersed as micelles (assembled by a single‐chain surfactant) or can form bilayer structures, such as liposomes. Depending on size, there are three types of liposomes: multilamellar vesicles (MLVs), small unilamellar vesicles (SUVs), and large unilamellar vesicles (LUVs).
16. Scheme 12.13 Schematic illustration of the floating peroxyl radical hypothesis for methyl linoleate (Barclay 1993). Methyl linoleate can be dispersed in micelles of surfactant or in liposomes formed by saturated phospholipid. The attack of initiating radical, ROO^•, on MeLin, LH, generates the lipid radical, L^•, that is instantaneously oxidized to more polar LOO^•. Polar LOO^• diffuses rapidly from the hydrophobic region of the bilayer to the lipid/water surface (dashed arrow).
17. Scheme 12.14 (a) Structural model of a typical LDL particle. (b) Rate of LDL oxidation for three different concentrations of α‐tocopherol and the mechanism of tocopherol‐mediated peroxidation.
Chapter 14
1. Figure 14.1 General structure of tocopherols and tocotrienols.
2. Figure 14.2 Chemical structure of ascorbic acid and ascorbyl palmitate.
3. Figure 14.3 The chemical structures of α‐carotene (a), β‐carotene (b), ε‐carotene (c), and lycopene (d).
4. Figure 14.4 Conversion of β‐carotene to vitamin A.
5. Figure 14.5 The chemical structures of cryptoxanthin (a), lutein (b), zeaxanthin (c), rhodovibrin (d), rhodoxanthin (e), astaxanthin (f), and fucoxanthin (g).
6. Figure 14.6 Chemical structures of phenolic acids, flavonoids, stilbenes, and lignan.
Chapter 15
1. Figure 15.1 Illustration of antioxidant capacity dependency on reaction time. (a) Experiment where the antioxidant capacity depends on the selected reaction time. Curves T₁ to T₄ represent the net absorbance values obtained for increasing concentrations of Trolox (conventional standard); TE, Trolox equivalents, determined by the interpolation of absorbance at a given reaction time in the Trolox calibration curve assessed at the same reaction time. Note: for Trolox, in this assay, the calibration curve is the same along time. (b) Experiment where the antioxidant capacity is independent of the selected reaction time. Curves AC₁ to AC₄ represent the absorbance values obtained for increasing concentrations of a given standard compound with reaction kinetics similar to the sample. This figure is based on results obtained for the ABTS^•+ assay applied to a red wine sample (ο), with Trolox (♦) and tannic acid (∆) as standard compounds.
2. Figure 15.2 Application of the kinetic matching approach to red wine samples by representing relative antioxidant capacity (AC) values along reaction time for several possible kinetic matching standards using several antioxidant assays.
3. Figure 15.3 Configuration of the SI‐LOV manifold applied for the assessment of total antioxidant capacity using the ABTS^•+ method. For the sake of simplicity, the waste tubing connected in port 1 is not represented in the scheme. ABTS^•+, 2,2’‐azino‐bis‐(3‐ethylbenzothiazoline‐6‐sulfonate radical cation prepared in acetate buffer (pH 4.6, 50 mM); CCD, spectrometer; HC, holding coil; LOV, lab‐on‐valve device; SV, two‐way valve; W, waste.
4. Figure 15.4 Peak profile (ΔAbs versus time) obtained after injecting 1 μL of Trolox and tannic acid standards using ABTS^•+ solution as carrier, as examples of fast and slow acting antioxidant compounds, respectively.

Functional Food Science and Technology series

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Measurement of Antioxidant Activity & Capacity

Recent Trends and Applications

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