Characterization of polyphenol oxidase from blueberry (Vaccinium corymbosum L.)

- Polyphenol oxidase (PPO) is responsible for color degradation in blueberries.
- PPO kinetics, substrate specificity, chemical inhibition and heat inactivation were assessed.
- Temperature optima of 35 °C and pH optima of 6.1-6.3 were observed for blueberry PPO.
- PPO completely inactivated in 20 min at 85 °C, whereas, chemical inhibitors showed variable results.

Polyphenol oxidase (PPO) was extracted and characterized from high-bush blueberries. PPO showed an optimum activity at pH 6.1-6.3 and 35 °C, with the enzyme showing significant activity over a wide temperature range (25-60 °C). Catechol was the most readily oxidized substrate followed by 4-methylcatechol, DL-DOPA, and dopamine. Blueberry PPO showed a Km of 15 mM and Vmax of 2.57 ΔA420 nm/min × 10−1, determined with catechol. PPO was completely inactivated in 20 min at 85 °C, however, after 30 min at 75 °C it showed about 10% residual activity. Thermal treatment at 55 and 65 °C for 30 min resulted in the partial inactivation of PPO. Ascorbic acid, sodium diethyldithiocarbamic acid, L-cysteine, and sodium metabisulfite were effective inhibitors of PPO at 1.0 mM. Benzoic acid and cinnamic acid series inhibitors showed relatively weak inhibition of PPO (21.8-27.6%), even at as high as 2.0 mM concentration.