Influence of heat treatment on inactivation of polyphenol oxidase enzyme

Abstract

The object of the study is fruit purees obtained from the raspberry (R), strawberry (S), and aronia (A) fruits. Raw materials were washed, shredded, and homogenized separately in an electric blender. A comparative assessment of the combination treatments was carried out. For this the fruit purees were divided into 4 replicates with obtaining the following samples: P-1 (ultrasonicated puree at 70˚C for 12 min. and sterilized at 105˚C, for 1.1 min.), P-2 (puree ultrasonicated at 70˚C, for 13 min. and sterilized at 105˚C, for 2.3 min.), P-3 (ultrasonicated puree at 70˚C, for 12 min. and sterilized at 105˚C, for 3.4 min.), P-4 (ultrasonicated puree at 70˚C, for 13 min. and sterilized at 105˚C for 4.5 min.) in comparison with P-0 sample (ultrasonicated puree at 70˚C). The enzyme activity of PPO was determined by a method based on the ability of PPO to oxidize pyrocatechol to quinone, which in turn oxidizes ascorbic acid. The result was calculated by the reaction rate in conventional units and expressed per 1 g of fruit puree (f.u.). The best results with a decrease of the PPO inactivation were shown by sample PA-1 where it presented a value of

30 f.u., PA-2- 25 f.u., PA-3- 14 f.u., and PA-4 - 3 f.u., in comparison with sample PA-0 which presented a value of 37 f.u. Similarly, raspberry purees also showed corresponding values, with a decreasing trend, where sample PZ-1 showed a value of 37 f.u., sample PZ-2- 26 f.u., sample PZ-3- 19 f.u., and PZ-4- 6 f.u., compared to sample PZ-0 which showed a value of 42 f.u. Strawberry purees recorded values similar to aronia purees and raspberry purees, where PC-1 showed a value of 46 f.u., PC-2- 32 f.u., PC-3- 24 f.u., and PC-4- 13 f.u., compared to sample PC-0 with a value of 51 f.u. Thus, the inactivation rate of PPO enzyme on ultrasonication and sterilization of fruit purees constitutes 97% for aronia puree, 94% for raspberry puree, and 87% for strawberry puree.