Determination of polyphenol oxidase (PPO) activity, anthocyanin contents and the phytonutrient changes in blueberry juice as influenced by different processing methods

Inhibition of blueberry PPO activity by sodium benzoate, potassium sorbate and potassium metabisulfite and their influence on degradation of individual anthocyanins in an extract was studied. Maceration of blueberries was carried out at 55°C for 1h with the addition of 0.1% sodium benzoate or with blanching pretreatment at 90°C for 1min. After maceration pretreatments the extracted juice was processed with traditional hot fill pasteurization, high hydrostatic pressure (HHP) and pulsed electric field (PEF).;Sodium benzoate and potassium metabisulfite were very effective PPO inhibitors in concentrations of 0.1% and 10ppm, respectively. Potassium sorbate was the weakest inhibitor, with 50% PPO remaining.;Degradation of anthocyanins by PPO was dependent on their structure. Tri-phenolic anthocyanins experienced the most degradation, followed by diphenolic and monophenolic compounds, respectively. Sodium benzoate was the most effective at preventing anthocyanin degradation; potassium metabisulfite did not have any protective effect, while potassium sorbate increased anthocyanin degradation.;Blanching of blueberries inactivated native PPO, but also increased the degradation of anthocyanins, especially malvidin glycosides. Addition of 0.1% sodium benzoate decreased PPO activity when compared to frozen blueberries but not in respect to control maceration.;Only 12% of anthocyanins and 33-41% of phenolics were extracted into juice from the frozen fruit. Hot fill pasteurization, high hydrostatic pressure and pulsed electric field did not significantly influence anthocyanins, phenolics and antioxidant activity in blueberry juice.