Polyphenol oxidase (PPO) from fresh-cut Chinese water chestnut (CWC) was extracted and the effect of citric acid on the PPO activity assayed. Citric acid at low concentrations stimulated PPO activity, but at 0.1 M or higher markedly inhibited the activity. On the basis of the inhibition of PPO activity in vitro, the use of 0.1 M citric acid for shelf life extension and quality maintenance of fresh-cut CWC was investigated. Fresh-cut CWC were dipped in a solution of 0.1 M citric acid, placed in trays over-wrapped by plastic films, and then stored at 4 degreesC. Changes in surface discoloration, eating quality and disease incidence were evaluated. Treatment with 0.1 M citric acid markedly extended the shelf life, inhibited surface coloration and disease development, and reduced the loss in eating quality associated with the contents of ascorbic acid and total soluble solid, titratable acidity and ascorbic acid. It is suggested that application of citric acid better maintained quality and extended shelf life of fresh-cut CWC. (C) 2003 Elsevier Ltd. All rights reserved.