Experiments were performed to optimise the extraction conditions of
“StarkingÏ apple fruit polyphenoloxidase (PPO), to evaluate the affinity and speciÐcity
towards several substrates and to study the stability of enzyme extracts
from apple samples stored under di†erent conditions. Sodium phosphate bu†er
(0É2 M, pH 6É5) plus 0É25% Triton X and 1% or 2% PVPP was found to be the most efficient extraction mediu10m0. Chlorogenic acid, dopamine and 4-
methylcatechol showed similar speciÐcity towards PPO, and chlorogenic acid
was found to be the best substrate for the enzyme. Enzyme extracts from frozen
cut apple stored at [4¡C, and extracts from lyophilised apple samples stored at
4¡C were more stable than extracts obtained from fresh-cut or acetone powder
sample
