Isolation and characterization of a ‘quinone‐trapping’ substance from a crude Carica papaya protein preparation

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.

Extraction and Characterization of Polyphenol Oxidase in Pawpaw (Asimina Triloba) Fruit

“…2005). PPO catalyzes mono‐ and o ‐diphenol conversion to o ‐quinones during ripening and during postharvest handling, storage and processing (Richard‐Forget et al. 1998; Nkya et al.…”

“…The enzyme PPO (EC 1.10.31) is found in the tissue of a wide range of fruits and vegetables, and is responsible for the browning discoloration observed in many plant food materials (Dry and Robinson 1994;Broothaerts et al 2000;Chen et al 2000;Okot-Kotber et al 2002;Leja et al 2003;Yang et al 2004;Casado-Vela et al 2005). PPO catalyzes mono-and o-diphenol conversion to o-quinones during ripening and during postharvest handling, storage and processing (Richard-Forget et al 1998;Nkya et al 2003;Casado-Vela et al 2005;Selles-Marchart et al 2006;Spagna et al 2005).…”

“…PPO extracted from most plants and fruits is capable of oxidizing o-diphenol, while mushroom PPO can catalyze both mono-and o-diphenol oxidation (Cash et al 1976). Because PPO-catalyzed oxidative reaction in fruits and vegetables could negatively affect the appearance, its presence in fresh products could reduce their shelf life and consumer acceptance, and therefore, their economical value (Richard-Forget et al 1998;Nunez-Delicado et al 2005).…”

Inhibition of endive (Cichorium endivia L.) polyphenoloxidase by a Carica papaya latex preparation

“…These products do not aect the oxygen uptake, but react with the 4-methylcatechol oxidation products as reported by Richard-Forget et al (1998). This lag phase is caused by cysteine and a dipeptide (glutamic acid±cysteine) in the commercial papaya latex preparation.…”

“…Thus, low molecular weight compounds exhibiting PPO-inhibitory properties have been detected in cultures of Dactylum dendroõÈ des (Harel et al, 1967), in potato (Nilova et al, 1973) and mushroom (Madhosingh, 1975) extracts. Richard-Forget et al (1998) have demonstrated that commercial papain preparations (from papaya latex) contain some substances which act as`quinone-trapping' materials. Tan & Harris (1995) found that products of the Maillard reaction inhibited apple PPO; similar observations were made by Tong et al (1995) with pectin preparations.…”