DPPH (1,1-diphenyl2-picrylhydrazyl) is a stable free radical because of its spare electron delocalization over the whole molecule. The DPPH assay, which is one of the best-known, frequently employed, and accurate methods. The delocalization causes a deep violet color with λmax around 520 nm. When a solution of DPPH is mixed with a substrate acting as a hydrogen atom donor, a stable nonradical form of DPPH is obtained with simultaneous change of the violet color to pale yellow[1].
DPPH assay has been successfully utilized for investigating antioxidant properties of wheat grain and bran, vegetables, conjugated linoleic acids, herbs, edible seed oils, and flours in several different solvent systems including ethanol, aqueous acetone, methanol, aqueous alcohol and benzene [2,3]. DPPH assay is a convenient method for the antioxidant assay of cysteine, glutathione, ascorbic acid, tocopherol and polyhydroxy aromatic compounds [4], for olive oil, fruits, juices and wines [5].
DPPH（1,1-二苯基-2-丙酰肼基）是一种稳定的自由基，因为它在整个分子上具有多余的电子离域作用。DPPH测定法是最著名、常用且准确的方法之一。离域导致深紫色竹最大约520纳米。当DPPH的溶液与充当氢原子供体的底物混合时，获得稳定的非自由基形式的DPPH，同时紫色变为浅黄色[1]。
DPPH测定法已成功用于研究小麦颗粒和麸皮、蔬菜、共轭亚油酸、草药、食用籽油和面粉在几种不同溶剂体系中的抗氧化性能，包括乙醇、丙酮水溶液、甲醇、乙醇水溶液和苯[2，3]。DPPH测定法是对橄榄油、水果、果汁和葡萄酒中半胱氨酸、谷胱甘肽、抗坏血酸、生育酚和多羟基芳香族化合物[4]进行抗氧化测定的一种方便方法[5]。
References:
[1]. Szabo M, Idi?oiu C, Chambre D, et al. Improved DPPH determination for antioxidant activity spectrophotometric assay[J]. Chemical Papers, 2007, 61(3): 214-216.
[2]. Yu L. Free radical scavenging properties of conjugated linoleic acids[J]. Journal of Agricultural and Food Chemistry, 2001, 49(7): 3452-3456.
[3]. Parry J, Su L, Luther M, et al. Fatty acid composition and antioxidant properties of cold-pressed marionberry, boysenberry, red raspberry, and blueberry seed oils[J]. Journal of agricultural and food chemistry, 2005, 53(3): 566-573.
[4]. Nishizawa M, Kohno M, Nishimura M, et al. Non-reductive scavenging of 1, 1-diphenyl-2-picrylhydrazyl (DPPH) by peroxyradical: a useful method for quantitative analysis of peroxyradical[J]. Chemical and Pharmaceutical bulletin, 2005, 53(6): 714-716.
[5]. Sanchez-Moreno C. Methods used to evaluate the free radical scavenging activity in foods and biological systems[J]. Food science and technology international, 2002, 8(3): 121-137.
