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Title: Elucidation of the mechanism of enzymatic browning inhibition by sodium chlorite

Author
item HE, QIANG - SICHUAN UNIV, CHINA
item Luo, Yaguang - Sunny
item Chen, Pei

Submitted to: Journal of Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2008
Publication Date: 5/20/2008
Citation: He, Q., Luo, Y., Chen, P. 2008. Elucidation of the mechanism of enzymatic browning inhibition by sodium chlorite. Journal of Food Chemistry. 110(4):847-851.

Interpretive Summary: Controlling cut-surface brown discoloration and the growth of disease causing microorganisms is critical for maintaining the quality and wholesomeness of fresh-cut apples. However, the fresh-cut industry faces a major technical challenge due to the incompatibility between the chemicals used for microbial control and browning inhibition. Our earlier study identified a chemical, sodium chlorite (SC), that effectively inhibited both pathogen growth and browning of fresh-cut apples. Since the browning of cut apples is caused primarily by a particular enzyme (PPO), this study was undertaken to investigate the inhibitory effect of SC on this enzyme. We found that the application of SC significantly reduced PPO enzyme activity, and also had the potential to remove the substrate for the enzyme, thus resulting in a significant inhibition in the browning reaction. These findings confirmed our theory that SC can be effectively used for browning control leading to the improvement in food quality and safety of fresh-cut produce.

Technical Abstract: Sodium chlorite (SC) is a well known anti-microbial agent and its strong inhibitory effect on enzymatic browning of fresh-cut produce has recently been identified. We investigated the mechanisms of browning inhibition by SC using chlorogenic acid (CA) and PPO extracted from mushroom to emulate the browning reaction. Results indicate that the browning reaction of CA (1.0 mM) catalyzed by PPO (33 U/mL) was significantly inhibited by 1.0 mM SC at pH 4.6. Two PPO isoforms were identified by native polyacrylamide gel electrophoresis, and both were inactivated by SC (3.0 mM). This suggests that SC serves as a PPO inhibitor to prevent enzymatic browning. Furthermore, the effect of SC on the stability of CA in both acidic (pH 4.5) and basic conditions (pH 8.3) was studied by UV-Vis scan and LC-MS analysis. The results showed that SC (3.0 mM) could remove CA from the reaction mixture by oxidative degradation of CA (0.1 mM). Hence, the anti-browning property of SC can be attributed to the two modes of action: the inactivation of polyphenol oxidase directly and the removal of phenolic substrates via oxidative degradation.