A Survey on the Potential Mode of Inhibition for Oxalic Acid on Polyphenol Oxidase

Abstract

The potential mode of inhibition for oxalic acid on polyphenol oxidase (PPO) was investigated. The extent of inhibition was influenced not only by oxalic acid concentration but also by pH. Inhibition was most prominent at pH 4.0 where complete inhibition occurred at the 4-mM oxalic acid concentration and was less evident at higher pH values. Inhibition of PPO by oxalic acid was due to its binding with copper to form an inactive complex, and the inhibition was characterized as noncompetitive. Oxalic acid diminished the catecholquinone product formation, and no quinone bleaching was observed. Oxalic acid was a more potent inhibitor of PPO compared with other structurally related acids.

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“…24,[27][28][29] It is also possible that the prevention of browning in litchi pericarp could be due to low pH. Oxalic acid, a chelating agent, is also acidulant, pH reducing, and is a prominent inhibitor of litchi pericarp browning.…”

Fresh-cut tropical and subtropical fruit products

“…They found that juices at 20% concentration containing 67 mg/100 g of oxalic acid inhibited browning. Yoruk and Marshall (2003) investigated the mode of inhibition of oxalic acid on PPO and determined that, by binding with copper to form an inactive complex, it reduces catechol-quinone product formation. Oxalic acid was a more potent inhibitor of PPO compared with other structurally related acids.…”

Peaches and Nectarines

“…A number of alternatives to sulfites like ascorbic acid, citric acid, 4-hexylresorcinol, erythorbic acid, and sodium erythorbate (stereoisomers of ascorbates), benzoic acid, honey, and natural fruit juices (e.g., lemon juice) have been tried with varying success. Chitosan coating (Huaqiang et al 2004), sodium hexametaphosphate (Pilizota and Sapers 2004), oxalic acid (Yoruk and Marshall 2003), and NatureSeal TM , a commercially available product containing calcium ascorbate (Arvind et al 2004), are the other alternatives tried more recently either alone or in conjunction with other inhibitors. In case of peach and nectarine, postcutting dips in ascorbate and calcium lactate, or use of modified atmosphere packaging (MAP) have shown to prolong the shelf life of fresh-cut slices (Gorny et al 1998).…”