Destabilization of thermostable, polyphenol oxidase (TS-PPO) during the ripening of peaches has been previously shown (Yemenicioglu, A.; Cemeroglu, B. Tr. J. Agric. For. 1998, 22, 261-265). This work studied the effect of ripening on thermal stability of apricot PPO for three different cultivars. Kabaasi cultivar contained thermolabile PPO, whereas TS-PPO appeared in Hacihaliloglu and Cataloglu cultivars. The TS-PPO showed biphasic inactivation curves, and its D and z values between 60 and 90 degreesC varied in the ranges of 357-1.12 min and 11.9-12.7 degreesC, respectively. In Hacihaliloglu cultivar the TS-PPO was very consistent and existed at all stages of ripening, whereas in Cataloglu cultivar it appeared only at the half-ripe stage. The loss of consistent TS-PPO in Hacihaliloglu apricots after partial purification by acetone precipitation and DEAE-cellulose chromatography suggested the non-covalent nature of its stabilization. The main purified fractions (F1 and F2) showed monophasic inactivation curves with similar thermal inactivation parameters (z(F1) = 10.4 degreesC, z(F2) = 10.1 degreesC). However, their kinetic properties against catechol (K-mF1 = 61 mM, K-mF2 = 122.7 mM) and substrate specificities were considerably different. The results of this study showed the presence of TS-PPO forming and destabilizing mechanisms in apricots. Further studies are needed for the solution of these mechanisms and to develop some new strategies that may be utilized by molecular techniques for a planned production of apricot cultivars provided with heat labile but normal PPO activity.
