Free radical scavenging activity of curcuminoids
Three natural curcuminoids (curcumin (CAS 458-37-7), demethoxycurcumin, bisdemethoxycurcumin) and acetylcurcumin were compared for their ability to scavenge superoxide radicals and to interact with 1,1-diphenyl-2-picryl-hydrazyl (DPPH) stable free radicals. The results showed that curcumin is the most potent scavenger of superoxide radicals followed by demethoxycurcumin and bisdemethoxycurcumin. Acetylcurcumin was inactive. Interaction with DPPH showed a similar activity profile. The study indicates that the phenolic group is essential for the free radical scavenging activity and presence of methoxy group further increases the activity. 
Radical scavenging ability of polyphenolic compounds towards DPPH free radical
Free radical scavenging activity of different polyphenolic compounds commonly present in wine has been evaluated using DPPH method. The experiments were performed with different amounts of phenols within the linear interval of response and with an excess of DPPHradical dot in all cases. In these conditions, for most of the compounds tested, the reaction was biphasic. Total stoichiometry values n confirm the implication of more than one step in the process. Flavan-3-ol compounds showed the highest values, especially procyanidins B1 (9.8) and B2 (9.1). In this family, n values coincide with the number of hydroxyl groups available. EC50 and TEC50 parameters have been calculated. EC50 values are extremely diverse, being the procyanidins B1 and B2 the most potent scavenging compounds and resveratrol the less one. TEC50 considers the rate of reaction towards the free radical. (+)-Catechin and (−)-epicatechin are the phenolic compounds that need more time to react. In contrast, caftaric and caffeic acids are the phenolic acids that react more rapidly. Antioxidant efficacy (AE) is a parameter that combines both factors. Compounds as kaempferol, with a high EC50 value, could be considered as an antioxidant with low relevance, but instead shows the highest AE value of the phenolic compounds tested, due to its fast rate of reaction, what is of great biological importance. 
Methods Used to Evaluate the Free Radical Scavenging Activity in Foods and Biological Systems
Free radical generation is directly related with oxidation in foods and biological systems. Therefore, the search for methods to determine free radical scavenging is important. In this work are described the methods used for this purpose in both substrates as well as in specific cases of their application. The main methods comprise superoxide radicals scavenging (O2·-); hydrogen peroxide scavenging (H2O2); hypochlorous acid scavenging (HOCl); hydroxyl radical scavenging (HO.); peroxyl radical scavenging (ROO.), among them are the methods that use azo-compounds to generate peroxyl radicals, such as the “TRAP” method (Total Radical-Trapping Antioxidant Parameter) and the “ORAC” method (Oxygen-Radical Absorbance Capacity); the scavenging of radical cation 2,2-azinobis-(3-ethylbenzothiazoline-6-sulphonate) or the ABTS or the “TEAC” method (Trolox Equivalent Antioxidant Capacity); the scavenging of stable radical 2,2-diphenyl-1-picrylhydrazyl or DPPH . method and the scavenging of radical cation N,N-dimethyl-p-phenylenediamine or DMPD method. At present, in spite of the diversity of methods, there is a great need to standardize measurements of antioxidant activity. The search for more specific assays, giving us chemical information that could be related directly to oxidative deterioration of foods and biological systems could be the objective of future research. 
Free Radical Scavenging and In-vitro Antioxidant Effects of Ethanol Extract of the Medicinal Herb Chromolaena odorata Linn
The ethanol extract of the leaf of Chromolaena odorata (Linn) was assessed for free-radical-scavenging and antioxidant potentials. Ability of the extract to scavenge reactive intermediates (superoxide ion O2Î‡-, hydrogen peroxide H2O2, nitric oxide NOË™, hydroxyl radical OHË™) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, were used to assess its free radical scavenging potentials. Antioxidant potential was studied by assessing in-vitro inhibition of lipid peroxidation in both the brain (Neuro-protective potentials) and liver homogenates of Fenton-oxidant stressed rabbits. Inhibition of protein oxidation was assessed in-vitro by loss of protein thiol (P-SH), while assessment of the reducing power of the extract was further used to assess antioxidant capacity. Results obtained showed the ability of the extract to scavenge free radicals and reactive intermediates in a dose-response manner. The plant also had good antioxidant capacity. The secondary plant metabolites found earlier in the extract may explain reasons for the bio-efficacy of the plant. These findings are of great importance in view of the availability of the plant and its observed possible diverse applications in medicine and nutrition.
Chemical Evaluation, Free Radical Scavenging Activities and Antimicrobial Evaluation of the Methanolic Extracts of Corn Silk (Zea mays)
Corn silk is thought to possess medicinal properties according to Nigerian folklore. This study was undertaken to appraise its phytochemical constituents and anti-microbial activities. Data obtained revealed that alkaloids, flavonoids, tannins, saponins, steroids, glycosides and cardiac glycosides were detected in the fresh mature and dried mature samples (FMCSS and DMCSS). The antioxidant activity of the extracts was determined by the DPPH inhibition method. The crude extract of the FMCSS exhibited a stronger free radical scavenging activity than that of the DMCSS (76.14: 73.54, 75.76: 68.23, 68.18: 61.46 and 64.18: 41.58% for the fresh versus the dried samples at 5, 3, 2 and 1 mg/ml concentrations). Results showed that when tested against Staphylococcus aureus, Pseudomonas aeruginosa, Klebsciella pneumonia, Escherichia coli and Salmonella thypi, the zones of inhibition obtained ranged from 10 to 16 mm for the fresh samples and between 12 to 20 mm for the dried samples. Mineral analysis revealed the presence of calcium (0.1869: 0.0610 mg/g), iron (0.005: 0 mg/g), magnesium (0.1939: 0.0934 mg/g), copper (0.0073: 0.0094 mg/g), manganese (0.0109: 0.0027 mg/g) and zinc (0.0165: 0.0146 mg/g) in the dried immature/mature silk. The results obtained suggested that the DMCSS sample studied plant possess better anti-bacterial activity with the major activity tailored to the phyto-constituents. GCMS analysis of the hexane extract of the silk showed the presences of straight chain alkanes and poly unsaturated methyl esters. 
 Sreejayan, N. and Rao, M.N., 1996. Free radical scavenging activity of curcuminoids. Arzneimittel-forschung, 46(2), pp.169-171.
 Villaño, D., Fernández-Pachón, M.S., Moyá, M.L., Troncoso, A.M. and García-Parrilla, M.C., 2007. Radical scavenging ability of polyphenolic compounds towards DPPH free radical. Talanta, 71(1), pp.230-235.
 Sánchez-Moreno, C., 2002. Methods used to evaluate the free radical scavenging activity in foods and biological systems. Food science and technology international, 8(3), pp.121-137.
 Alisi, C.S., Ojiako, O.A., Osuagwu, C.G. and Onyeze, G.O.C., 2011. Free Radical Scavenging and In-vitro Antioxidant Effects of Ethanol Extract of the Medicinal Herb Chromolaena odorata Linn. Journal of Pharmaceutical Research International, pp.141-155.
 Emmanuel, S.A., Olajide, O., Abubakar, S., Akiode, S.O. and Etuk-Udo, G., 2016. Chemical evaluation, free radical scavenging activities and antimicrobial evaluation of the methanolic extracts of corn silk (Zea mays). Journal of advances in medical and pharmaceutical sciences, pp.1-8.
Free radical scavenging activity of curcuminoids