PPO activity and polyphenol content are not limiting factors during brown cove development in pears (Pyrus communis L-cv. conference)

Brown core is a disorder in pears that is frequently observed in the Confer ence cultivar. The brown colour is the: result of an enzymatic oxidation of polyphenol substances to a-quinones, a reaction catalysed by polyphenoloxi dases (PPO). In a later stage pears can form cavities in and nearby the cor e. The goal of our research was to understand and predict the development of c ore browning. Pears from orchards in Spain and The Netherlands were compare d to observe climatic influences on the development of brown core. PPO acti vity and total polyphenol content are not affected by harvest date, storage atmosphere and orchard, and both do not seem to be limiting during develop ment of brown core. An observed decrease of tyrosinase activity might be th e consequence of the decreased viability of brown tissue. We hypothesize th at core browning is induced by decompartmentation of intracellular membrane structures.