Inhibitory effects of thiol compounds on theaflavin browning and structural analysis of the causative substances. (1st August 2022)

• Record Type: Journal Article
• Authors: Narai-Kanayama, Asako; Chiku, Kazuhiro; Ono, Hiroshi; Momoi, Takamitsu; Hiwatashi-Kanno, Miho; Kobayashi, Akiko; Matsuda, Hiroko; Yoshida, Mitsuru; Nakayama, Tsutomu
• Is Part Of: Food chemistry. Volume 384(2022)
• Publication Date: 2022-08-01
• Subjects: DTNB 5, 5-dithiobis(2-nitrobenzoic acid) -- EGCg (−)-epigallocatechin gallate -- GSH glutathione -- MeCN acetonitrile -- NAC N-acetyl-l-cysteine -- SOD superoxide dismutase; Theaflavin -- Thiol group -- Cysteine -- Glutathione -- N-acetyl cysteine; Food -- Analysis -- Periodicals; Food -- Composition -- Periodicals; 664
• DOI: 10.1016/j.foodchem.2022.132488
• Languages: English
• ISSNs: 0308-8146

Abstract

Highlights: Theaflavin, a phenolic pigment of black tea, is unstable in aqueous solutions. Browning of theaflavin solutions was inhibited in the presence of thiol compounds. Theaflavin and thiol compounds decreased in the solutions to form reaction products. Chemical structures of the products were first identified. Abstract: Theaflavin, a polyphenol responsible for the bright orange color and various bioactivities of black tea exudates, is susceptible to autoxidation at neutral and mild alkaline pH, changing its color to brown. In the presence of cysteine (Cys), glutathione (GSH), or N -acetyl cysteine (NAC), the browning of theaflavin solution was inhibited concomitantly with time-dependent decreases in the concentrations of both theaflavin and thiol group. The rank order of the decrease was Cys ≅ GSH > NAC, suggesting the relevance of the nucleophilic property of the thiol group to its reaction with theaflavin. LC-MS analysis of the reaction products indicated formation of novel derivatives that were mono- or di-molecular adducts of thiol compounds. We determined the chemical structures of theaflavin-Cys and theaflavin-GSH adducts by NMR and proposed the reaction mechanisms. It was found that the theaflavin-Cys adduct was not a simple adduct, to which a new cyclic structure was added.