Isolation and characterization of a 'quinone-trapping' substance from a crude Carica papaya protein preparation |
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Authors: | Florence Richard-Forget Muriel Cerny Nina Fayad Thierry Saunier & Patrick Varoquaux |
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Affiliation: | 1 INRA, Station de Technologie, Domaine St Paul, Site Agroparc, F-84914 AVIGNON cedex, France; CNAM, Chaire de Biochimie Industrielle et Agro-Alimentaire, 292 Rue Saint Martin, 75141 Paris Cedex 03, France |
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Abstract: | The oxidation of different phenols 4-methylcatechol, chlorogenic acid, (?)-epicatechin and (+)-catechin] by endive polyphenoloxidase (PPO) was investigated in the presence of an extract from Carica papaya . The occurrence of cysteine and another 'quinone-trapping' substance in the extract was demonstrated. The unknown substance was purified, as a 4-methylcatechol conjugate form, by a combination of Bio-gel Pz chromatography and semipreparative high-performance liquid chromatography (HPLC). Use of liquid chromatography/tandem mass spectroscopy (LC–MS/MS) equipment and an amino acid analyser allowed us to identify this agent as a dipeptide cysteine-glutamic acid, commercially available as γ-Glu-Cys. γ-Glu-Cys formed one adduct compound with 4-methylcatechol and chlorogenic acid, and two with the flavan-3-ols. The thiol adducts were not substrates for endive PPO but, in the case of the 4-methylcatechol conjugate, they acted as competitive PPO inhibitors. |
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Keywords: | Enzymatic browning inhibition papain polyphenoloxidase thiol compounds |
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