Development of a Rapid Method for the Evaluation of DPPH Radical Scavenging Activity of Ginger ( Zingiber officinale ) F
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Development of a Rapid Method for the Evaluation of DPPH Radical Scavenging Activity of Ginger (Zingiber officinale) Foods Based on Cyclic Voltammetry Liu Jiang 1 & Xin Li 1 & Dongfeng Wang 1
Received: 19 August 2016 / Accepted: 17 October 2016 # Springer Science+Business Media New York 2016
Abstract A new and rapid method based on cyclic voltammetry (CV) was proposed for the evaluation of 2,2-diphenyl-1picryhydrazyl (DPPH) radical scavenging activity (RSA) of ginger (Zingiber officinale Roscoe) foods. The extraction conditions of samples were optimized by an orthogonal L9(3)4 test. Under optimum condition (methanol, solid–liquid ratio 1:3 and ultrasonic for 30 min), the ginger extracts were prepared and the electrochemical parameters of extracts were determined. The results show that two electrons and two protons are involved in the electrochemical oxidation. The evaluation method of DPPH-RSA was developed using the CV method. Eight kinds of ginger foods were evaluated using the proposed method. The results from the CV method and the classical spectroscopic method show insignificant difference ( solvent > solid– liquid ratio > immersing time. The optimum conditions are A3B3C1D3, that is, to use methanol as solvent with the
Table 2 Analysis of an orthogonal L9(3)4 test
solid–liquid ratio equals to 1:3 and ultrasonic for 30 min. This condition was used to prepare the ginger extracts and those of the ginger foods. CV Behavior of Ginger To study the CV behaviors of ginger extracts, the fresh ginger extract and the dry ginger extract (made from the same amount of fresh ginger) were tested. Fig. S1 shows the CV curves of ginger extracts in 0.05 M PBS buffer solution (pH 7.0) in the potential range from −0.6 to 0.8 V with a scan rate of 0.20 V· s−1, where a, b, and c are CV curves of fresh ginger extract, dry ginger extract, and GCE, respectively. As shown in the figure, the GCE shows no peak in PBS buffer solution. After 1.0 mL of ginger extract was added, a pair of redox peaks was observed with the anodic peak potential (Epa) and the cathodic peak potential (Epc) equaled to 0.10 and 0.18 V, respectively. The absolute difference |Epa − Epc| was greater than 0.057 V, inferring that the electrode reaction of ginger extract on GCE is a quasi-reversible oxidation-reduction (Mabbott 1983; Wang 2006). In addition, there is a distinct peak in oxidation at Epa = 0.46 V, which was suspected to be the irreversible oxidation reaction of antioxidant in the ginger extract or oxygen. Indeed, the ginger antioxidant substances are a complex mixture where gingerol, shogaol, and diphenylheptane compounds are the major components (Shukla and Singh 2007). From the molecular point of view, these major components share the same electroactive group, the guaiacol group, but the main difference between them is the number of carbon atoms
No.
(A) Method
(B) Solvent
(C) Solid–liquid ratio (g/mL)
(D) Immersing time (min)
ipa (10−8 A)a
1 2 3 4 5 6 7
1 1 1 2 2 2 3
1 2 3 1 2 3 1
1 2 3 2 3 1 3
1 2 3 3 1 2 2
4.51 3.83 5.31 7.75 7.83 10.4
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