Kinetics of polyphenol oxidase activity inhibition and browning of avocado puree preserved by combined methods

Enzymatic browning reactions limit the commercial shelf life of avocado puree, thus color preservation throughout storage becomes one of the main objectives for fruit processors. The aim of this work was to model the color changes that occurred in avocado puree preserved by combined methods during four months under refrigeration. Changes in polyphenol oxidase (PPO) activity and color were successfully described by first-order models. PPO activity decays Could be described by a simple first-order kinetic with rate constants of 4.4 x 10(-3)-40.0 x 10(-3) day(-1). On the other hand, browning (DeltaE*) of puree was due to L* and, in a minor extent, to a* changes, whereas b* did not change significantly throughout time. A fractional conversion kinetic suited color data with high R-2 coefficients and a good fitting to experimental values in the wide range of tried conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.