The Use of Polyphenol Oxidase Activity to Identify a Potential Raisin Variety

The biochemical characterization of polyphenol oxidase (PPO) in the white grape Bianchetta Trevigiana is addressed in this research to fulfil the requirement for raisin varieties with high concentrations of phenolic compounds and low PPO activity not only to avoid enzymatic browning but also for maintaining the nutritional value of raisins. Spectrophotometric assays and electrophoresis were used to study this ancient variety exhibiting low PPO activity (only cathecolase activity) which reached at the low pH value of grape berry and was about 15% of the maximum enzymatic activity measured. In addition, the visualization of the active isoforms of grape PPO after 2-DE separation of proteins was a key step for further studies using MALDI-TOF-MS and bioinformatic tools. Based on the thermal inactivation profiles, heating treatment at 70°C may be considered a way to inhibit Bianchetta Trevigiana PPO activity by preserving also its high phenolic content. Therefore PPO characterization may be proposed as a marker for identifying potential high value raisin varieties.