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Kinetic Study of the Radical Scavenging of Capsaicin in Homogeneous Solutions and Aqueous Triton X‐100 Micellar Suspensions
Author(s) -
Watanabe Atsushi,
Seno Shinichiro,
Kogure Eiki,
Seki Kensuke,
Sakamoto Takeshi,
Okada Youji,
Shimazu Hideaki
Publication year - 2015
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/1750-3841.12798
Subject(s) - chemistry , aqueous solution , radical , triton x 100 , micellar solutions , methanol , reaction rate constant , scavenging , nuclear chemistry , inorganic chemistry , kinetics , micelle , organic chemistry , antioxidant , pulmonary surfactant , physics , quantum mechanics , biochemistry
A kinetic study of capsaicin (CAP) toward radicals has been performed using stopped‐flow spectrophotometry in detail. The second‐order rate constants ( k 2 ) for the reaction of CAP toward 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and galvinoxyl have been measured in methanol, ethanol, 2‐propanol/water (5:1, v/v), and aqueous micellar suspensions containing 5% Triton X‐100 (pH 4.0 to 10.0), respectively. The decay rates of DPPH and galvinoxyl for the reaction with CAP increased linearly in a concentration‐dependent manner in homogeneous solutions and aqueous micellar suspensions. However, the k 2 for CAP obtained in an aqueous micellar suspension showed notable pH dependence; that is, the reactivity of CAP increased with an increasing pH value from 4 to 10. In addition, a good correlation between the k 2 value and the molar fraction of CAP (phenolate anion (CAP‐O − )/undeprotonated form (CAP‐OH)) was observed. These properties are associated with the p K a of CAP. Furthermore, it was found that the CAP‐O − reacts with galvinoxyl about 6 times as fast as the CAP‐OH. These results indicate that sequential proton loss electron transfer from the phenolic hydrogen of CAP may be responsible for the scavenging of radicals in an aqueous micellar suspensions.