DPPH method

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... 

The interaction of acrolein with a catalyst was investigated using a DPPH method (27), in which an acyl radical formed by the initiation was trapped by DPPH, and the rate of consumption of DPPH, corresponding to the rate of formation of the radical, was determined by visible light spectra. The rate equation for acyl radical formation is... 

Ozgen M, Reese RN, Tulio AZ Jr, Scheerens JC, Miller 7VR. Modified 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (abts) method to measure antioxidant capacity of Selected small fruits and comparison to ferric reducing antioxidant power (FRAP) and 2,2 -diphenyl-l-picrylhydrazyl (DPPH) methods. Journal of Agricultural and Food Chemistry. 2006 54(4) 1151-1157. 

Bhandari P, Kumar N, Singh B, Ahuja PS. Online HPFC-DPPH method for antioxidant achvity of Picrorhiza kurroa Royle ex Benth. and characterization of kutkoside by Ultra-Performance FC-elechospray ionizahon quadrupole ttme-of-flight mass spectrometry. Indian Journal of Experimental Biology. 2010 48 323-328. 

L18. Lissi, E. A., Modak, B., Torres, R., Escobar, J., and Urzua, A., Total antioxidant potential of resinous exudates from Heliotropium species, and a comparison of the ABTS and DPPH methods. Free Radic. Res. 30, 471-477 (1999). 

Since the crocin-bleaching method is based on competition kinetics, it can also be used to detect pro-oxidant activity (POA), for example, of early MRPs the DPPH method cannot. In fact, in the presence of antioxidants, the crocin-bleaching rate [reaction (1)] is slowed down, because the antioxidant reacts with the radical first and the antioxidant radical formed [reaction (2)] reacts only slowly with the crocin [reaction (3) ]. On the contrary, the pro-oxidant competes with the radical for the crocin [reaction (4)], thus increasing the extent of crocin bleaching 446... 

Peroxy radicals are known to be responsible for the bleaching of carotenoid pigments, such as crocin. Such bleaching can be inhibited by antioxidants.468 492 493 In determining the residual radical scavenging activity of tomato juice, crocin bleaching and the DPPH method gave parallel results 446... 

The free radical scavenging effects of compounds 57 derived from dihydro-pyrimidines 56 (Scheme 12) was also examined by the DPPH method and by measuring hydroxyl radical scavenging activity (RSA) [33]. It was found that compounds derived from the thioureas had the best antioxidant activities. Compounds 58 and 59 were the most potent and had comparable activity to quercetol (Table 4). 

Free radicals react most efficiently with other free radicals, and the chemicals that have relatively stable free radicals, such as 2,2-diphenyl-1-pricylhydrazyl (DPPH), could be used, in principle, to quantitatively estimate the amount of free radicals (DPPH method). The peroxide formed on the surface that derived from free radical could be quantitatively analyzed by the determination of iodine liberated from KI solution, which could be used to calculate the amount of the original free radical from that peroxide was derived (iodine method). 

Figure 30.24 Peroxide concentration on the various kinds of plasma-treated X-ray opaque powder surfaces determined by DPPH method.

The development of free radical scavenging capacity as determined by the DPPH method was studied during aging of selected red Spanish wines (Larrauri et al.,... 

Antioxidative assay. Antioxidative activity was measured by DPPH method [10,11]. 

Telysheva, G., Dizhbite, T., Tirzite D., Juijane V. Applicability of a free radical (DPPH-) method for estimation of antioxidant activity of lignin and its derivatives. 5th International lignin institute, Forum, Commercial outlets for new lignins and definitions of new projects, Bordeaux, France, Proceedings, pp. 153-160. (2000)... 

Catechin and epicatechin Extrusion Antioxidant activity evaluated with the DPPH method 65... 

Figure 7 Antioxidant capacity measurements obtained by the DPPH method. EPR signal intensities were determined at 60 s after mixing of the DPPH assay solution with each of the samples listed at the bottom of the automatically generated chart. From left to right, the test solutions were distilled water (control), ascorbic acid at 5, 2.5, 1.25, 0.625, and 0.3125 mM, distilled water, white wine, red wine.

Effect of radical density as a function of UV irradiation time as determined by the DPPH method. 

As previously mentioned, DPPH is soluble in organic solvents however, depending on the type of compound to be analyzed (extracts, cosmetics, foods), the solvent polarity may need to be raised by adding water for analyte dissolution, but this can cause precipitation of the DPPH radical. Therefore, Stasko et al. (2007) studied limits for water as a component of the mixed water-ethanol solvent in the analysis of antioxidant capacity by the DPPH method. They concluded that 50% water is a suitable choice for lipophilic and hydrophilic antioxidants, and the reaction rate increases considerably with increasing water ratios. However, in solutions that are more than 60% water, the antioxidant... 

The development of the DPPH method in aqueous solution using surfactant aggregates or micelles has also been studied (Noipa et al., 2011). When surfactants are added to DPPH radical aqueous solution at concentrations higher than the critical micelle concentration, they spontaneously form micelles with the hydrophobic tails pointed toward the center and the hydrophilic head groups pointed toward the surface of the micelle. Laguerre et al. (2014) utilized sodium dodecyl sulfate (SDS) as a surfactant. In this study, the concentration of SDS was varied (10, 20, and 60 mmol L ). After 25 min, a decrease of just 5% of the DPPH radical initial concentration was observed at all SDS concentrations. 

TABLE 29.2 Summary of Conditions Reported in Publications Using the DPPH Method... 

According to the results shown in Table 29.2, it can be observed that reaction time, solvent, and DPPH concentration vary according to the proposed method. Therefore, the comparison of antioxidant capacity obtained by the DPPH method for the same compounds is limited. Table 29.3 lists different ICjg (pM) values for some standard antioxidants, and the differences are probably due to the varied conditions used in each work. 

FIGURE 29,5 FIA system associated with the DPPH method and spectrophotometer detector. 

The SIA technique consumes even smaller volumes, and reagents and samples can be drawn sequentially and stacked into the mixing coil before mixing while being pushed in the reverse direction into the detector the system can also be programmed to stop for a desired period of time (Hartwell, 2012). This technique was adapted for the DPPH method (Polasek et ah, 2004 Koleckaf et ah, 2007 Rehakova et al., 2008). 

Multisyringe FIA is an automatic-flow method that combines the multichannel operation of FIA and the flexibility of multicommutation flow systems. In this system, the antioxidant capacity can be determined by the DPPH method for several samples using the stopped-flow condition, which enables the monitoring of the absorbance decrease with time and evaluation of the reaction kinetics (Magalhaes et al., 2006 Magalhaes et al., 2009 Kedare and Singh, 2011). The absorbance in the presence and absence of an antioxidant is measured, and the AA% or IC50 can be calculated as in the static spectro-photometric method. 

The antioxidant capacity obtained by the DPPH method can be determined by other spectroscopic techniques such as ESR, also known as electron paramagnetic resonance (EPR). This technique directly detects paramagnetic compounds (i.e., containing unpaired electrons). 

In the DPPH method with the ESR technique, the DPPH radical concentration in the sample is directly measured. The decrease in the ESR spectral amplitude becomes observable, indicating a decrease in the DPPH radical concentration. Eigure 29.7 shows the ESR spectra of a DPPH solution before and after reaction with an antioxidant, allowing observation of the decrease in the amplitude. 

TABLE 29,5 Antioxidant Capacity in Food Samples Obtained by the DPPH Method Using the ESR Technique... 

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