Cysteine Inhibition of Enzymatic Blackening with Polyphenol Oxidase from Potatoes

Abstract

SUMMARY The possible sites of cysteine inhibition of enzymatic blackening using polyphenol oxidase from potatoes were studied. The initial site of cysteine inhibition of enzymatic blackening caused by tyrosine oxidation occurred at the oxidation of tyrosine to 3,4‐dihydroxyphenylalanine (dopa). Following the initial induction period, the oxygen uptake paralleled those treatments with no cysteine. Concentrations of cysteine (9.5 × 10‐3M) which inhibited tyrosine oxidation for 100 min did not inhibit dopa oxidation significantly. However, higher concentrations (1.9 × 10‐2M) inhibited dopa oxidation. Cysteine did not inhibit chlorogenic acid oxidation under the conditions of our study. Oxygen uptake with chlorogenic acid plus cysteine was higher than in the absence of cysteine. Cysteine concentrations which effectively inhibited tyrosine oxidation did not inhibit oxidation in the presence of tyrosine plus chlorogenic acid.

Chemistry, Biochemistry, and Dietary Role of Potato Polyphenols. A Review

“…Browning Prevention. The sulfhydryl (SH or thiol) compounds such as cysteine, N-acetyl-L-cysteine, and reduced glutathione, as well as ascorbic and citric acids, are good inhibitors of the enzyme PPO which catalyzes enzymatic browning in fruits and vegetables including potatoes (Dudley and Hotchkiss, 1989;Friedman et al, 1991;Golan-Goldhirsh et al, 1994;Langdon, 1987;Matheis, 1987a,b;Matheis and Whitaker, 1984;Muneta, 1981;Muneta and Walradt, 1968;Sanchez-Ferrer et al, 1993;Sapers, 1993;Sapers andMiller, 1992, 1995). We showed that SH-containing amino acids and peptides are good inhibitors of both enzymatic and nonenzymatic browning in freshly prepared and commercial fruit juices, apples, fresh and dehydrated potatoes, heated amino acid-carbohydrate mixtures, and protein-rich foods (Friedman and Bautista, 1995;Friedman and Molnar-Perl, 1990;Molnar-Perl and Friedman, 1990a,b; Figure 7).…”

Cysteine as an Inhibitor of Polyphenol Oxidase

“…They believed that all three mechanisms operate simultanously . Muneta and Walradt (1968) suggested that an initial effect of Cys was to directly inhibit PPO. Kahn (1985) interpreted her data to mean that Cys initially inhibited browning by reducing o-quinones to odihydroxyphenols before they can polymerize to melanin.…”

Characterization and comparison of plant and crustacean polyphenol oxidases : kinetics and inhibition by chemical methods /

“…Other compounds acting as reducing agents which reduce o-quinones to diphenols or react with plant PPO substrates to lessen the extent of enzymatic browning are ascorbic acid, SOg, sodium sulfite, sodium bisulfite, sodium metabisulfite, potassium metabisulfite, cysteine, 2-mercaptoethanol , glutathione, benzenesulphinic acid, DIECA, Na-ethyl xanthate, and PVP (Cash et al, 1976;Embs and Markakis, 1965;Feinberg et al, 1976;Haisman, 1974;Hope, 1961; Markakis and Embs, 1966;Mapson, 1965;Mapson and Wager, 1961;Muneta, 1966;Muneta and Walradt, 1968;Muneta and Wang, 1977; Ponting, 1960; Ponting and Jackson, 1972; Sayavedra-Soto and Montgomery, 1986;Singh and Ahlawati, 1974;Taeufel and Voigt, 1964;Vamos-Vigyazo, 1981;Walker, 1964). For the prevention of melanosis in crustaceans, numerous agents including ascorbic acid and sodium ascorbate, ascorbate and citrate, L-tyrosine, L-methionine, citric acid, L-cysteine, sodium diethyl dithiocarbamate, sodium tripolyphosphate (STP), sodium sulfite, and sodium bisulfite have been broadly studied '1 1 (Antony and Nair, 1975; Bailey and Fieger, 1954;Faulkner et al .…”

“…Roston (1960 proposed that cysteine inhibits enzymatic blackening caused by the oxidation of L-tyrosine and DL-DOPA by forming addition products with qui nones. Muneta and Walradt (1968) studied potato PPO and found that the concentration of cysteine required for comparable inhibition was 5-fold higher with cysteine than for sulfite. These authors also noted that cysteine did not inhibit chlorogenic acid oxidation; and the oxidation of tyrosine to DOPA is more sensitive to cysteine inhibition than the oxidation of DOPA to dopaquinone.…”

“…These authors also noted that cysteine did not inhibit chlorogenic acid oxidation; and the oxidation of tyrosine to DOPA is more sensitive to cysteine inhibition than the oxidation of DOPA to dopaquinone. Both Muneta and Walradt (1968) and Henze (1956) proposed that cysteine inhibited enzymatic browning by combining with the quinone. The sulfiting agents have been postulated toreact with the enzyme or the quinones to exert the inhibitory effect (Joslyn and Ponting, 1951; Joslyn and Braverman, 1954).…”