The effects of Brassicacaea processing water on polyphenol oxidases from different plant sources were investigated. Results showed that processing water (PW) prepared by cooking young Brassicacaea leaves with water has the capacity to inhibit both commercial tyrosinase and plant polyphenol oxidases. PW was freeze-dried (LPW) in an attempt to increase its utility and improve its efficiency at inhibition of polyphenol oxidases, however this resulted in a loss of activity, probably due to the stresses of the freezing and/or drying processes. The addition of PW to ascorbic acid resulted in complete inhibition of grape polyphenol oxidase, suggesting that the combination of the two antibrowning agents may be a promising tool to control this enzymatic activity. (C) 2010 Elsevier Ltd. All rights reserved.