Isolation and catalytic actions of polyphenoloxidase from sunflower seeds (Helianthus annuus)

In the last few decades, biotechnological applications of phenoloxidase enzymes have become an area of significant interest. In this study, sunflower seeds, seedlings and defatted mill cake were investigated as possible plant source of polyphenoloxidase (PPO). Noticeable variation of chlorogenic acid concentration in each raw material has undoubtedly proven that only sunflower seedlings have significant amounts of active PPO. The activity of the enzymes was assessed by measuring the molar decrease of caffeic acid. Isolated protein powders from each raw material confirmed the presence of PPO only in the seedlings. Catalytic action of the PPO of seedlings was compared to that of the commercial laccase from Trametes versicolor. Sunflower PPO was selectively active on caffeic and chlorogenic acids, less active on ferulic acid and not active on mono-phenols and gallic acid. Conversely, laccase was highly active on all the assessed phenols. PPO activity was good in a large range of pH (4-8), whilst it was approximately halved in solutions containing 35% ethyl alcohol (v/v), 500 mg L⁻¹ citric acid and finally 200 mg L⁻¹ sulphur dioxide. In conclusion, sunflower seedlings can be considered a potential and interesting plant source of PPO. Sunflower PPO could be used to oxidise selectively o-diphenols, for example in alcoholic and nonalcoholic beverages