Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 2006
Publication Date: May 17, 2006
Citation: Lu, S., Luo, Y., Feng, H. 2006. Inhibition of apple polyphenol oxidase activity by sodium chlorite. Journal of Agricultural and Food Chemistry. 54:3693-3696.
Interpretive Summary: Enzymes that are present in apple tissue, primarily polyphenol oxidase, abbreviated PPO, cause browning in fresh-cut apple slices. This discoloration of the apple flesh is accompanied by changes that reduce the nutritional quality and affect taste as well as appearance. Browning causes economic losses because product that is unacceptable to consumers must be discarded. Most browning inhibitors that have been discovered are either very expensive, affect the taste of produce, or are associated with food safety concerns. Most anti-browning agents must be used with sanitizers to control growth of pathogens and spoilage bacteria, but many cancel the effect of these sanitizers. We found that a chemical called sodium chlorite reduced both bacterial growth and browning in fresh-cut apples, and so we did further studies to investigate the means by which sodium chlorite inhibits PPO. This information will be of interest to the fresh-cut fruit industry.
The mode of inhibition of sodium chlorite (SC) on polyphenol oxidase (PPO) from Red Delicious apples was investigated. The extent of inhibition was influenced by SC concentration and pH. Inhibition was most prominent at pH 4.5, where approximately 30% of the enzyme activity was lost in the presence of 10 mM SC, followed by pH 4.0 with a 26% reduction in PPO activity. The inhibition mode was determined using Dixon and Lineweaver-Burk plots, which established SC to be a mixed inhibitor of apple PPO for the oxidation of catechol. Preincubation of PPO with 8 mM SC for 8 min caused a maximum of 46% activity reduction compared to the non-inhibited control, providing further evidence that the inhibition of PPO activity by SC is due to the inhibition of the enzyme itself rather than the removal of the substrate.