Characterization and Inhibition of Polyphenol Oxidase From Pears (Pyrus Communis L. Cv. Bosc and Red)

Abstract

Red pears had higher PPO activity, total phenolics and chlorogenic acid concentration than Bosc pears. PPO activity and phenolics both decreased in fruits held at room temperature. pH and temperature optima for Bosc and Red pears PPOs were 5.0 and 5.5, and 20 and 23C, respectively. 4‐Methylcatechol, catechol and dopamine were good substrates for PPO from both pear cultivars; however, no activity was observed with any of the mono‐hydroxy substrates studied. Higher Km and lower Vmax values were observed for Bosc pear PPO. Heating at 75C for 30 min completely inactivated the enzyme from both cultivars. Heating at 55 and 65C for the same duration resulted in partial inactivation (45–60%) of this enzyme. Ascorbic acid, L‐cysteine, sodium metabisulfite and thiourea effectively inhibited browning due to pear PPOs.

Effect of chitosan coating on quality and nutritional value of fresh-cut and #8216;Rocha and #8217; pear

“…Taking into account that the maximum activity of pear PPO occurs at pH values between 4.3 and 5.5 (Espín et al, 1998;Siddiq et al, 1994), it was expected that chitosan solutions adjusted to pHs closer to neutral could reduce PPO activity, thus enhancing the antibrowning effect of the coating. In fact, when pear slices were treated with chitosan solutions with acidic pH, around 3, no differences were observed between control and chitosan treated slices (data not shown).…”

Polyphenoloxidases from Williams Pear (Pyrus communis L, cv Williams): Activation, Purification and Some Properties

“…A considerable variation was found in the optimum pH value and relative activity towards different phenols from one preparation to another (Halim and Montgomery 1978 ;Smith and Montgomery 1985 ;Zhou and Feng 1991 ;Siddiq et al 1994). Two isoforms were separated by Rivas and Whitaker (1973) and three by Wissemann and Montgomery (1983).…”

Consumer evaluation and quality measurement of fresh-cut slices of ‘Fuji,’ ‘Golden Delicious,’ ‘GoldRush,’ and ‘Granny Smith’ apples

“…However, it was scored barely acceptable in our preliminary test, was slimy to the touch, and was not in the formulations tested by Buta et al (1999), so we did not include it in our PQSL treatments. Cysteine and its derivatives were found to inhibit PPO activity in pear (Siddiq et al, 1994), and N-acetylcysteine specifically is used as a dietary supplement. We decided to use 100 mM isoascorbic acid, 5 mM Ca ascorbate, 5 mM Ca propionate, and 5 mM N-acetylcysteine for the PQSL processing treatment in Expt.…”

“…Browning can also be delayed by reducing agents such as ascorbic, isoascorbic, or citric acid, or by inhibitors of polyphenol oxidase (PPO) such as cysteine or 4-hexylresorcinol (Siddiq et al, 1994;Buta et al, 1999). In addition, antimicrobial substances such as Ca propionate and other food preservatives (Davidson and Juneja, 1990) may delay the secondary browning that can develop on apple slices contaminated by spoilage microorganisms.…”