Characterization of polyphenol oxidase from fennel (Foeniculum vulgare Mill.) seeds as a promising source

Fennel seeds were recognized as a promising polyphenol oxidase (PPO) source upon investigating some edible green plants (carob, jujube, coriander, fennel, and licorice). The fennel PPO enzyme was purified by three-phase partitioning and biochemically characterized in detail for the first time. The purification fold and activity recovery values were determined as 20-fold and 120%, respectively. Its molecular weight was 27.8 kDa. The temperature for the selected substrates (catechol, 4-tert-butylcatechol, 4-methylcatechol, and pyrogallol) was 30 degrees C, while the optimum pH value varied from 5.0 to 7.0 depending on the substrate. The k(cat)/Km values exhibited that the enzyme presented the best activity towards catechol among the substrates used. Sodium metabisulfite, ascorbic acid, benzoic acid, L-cysteine, thiourea, beta-mercaptoethanol, and glutathione prominently inhibited PPO activity. A remarkable decrease in PPO activity was observed at elevated concentrations of organic solvents, but in cases of the solvents with polarity indexes >= 5.1, the residual activity maintained more than 75% of its original activity up to 10% (v/v). Consequently, the current study suggested that fennel seeds could be used in various industrial sectors to produce low-cost polyphenol oxidase enzymes with an agricultural origin. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Fennel seeds were identified as a promising source of polyphenol oxidase (PPO) and the purified PPO enzyme was characterized in detail for the first time. The enzyme showed the best activity towards the substrate catechol, suggesting potential industrial applications in producing low-cost enzymes. Inhibitors and organic solvents were found to impact PPO activity, with certain solvents maintaining the enzyme's activity at high concentrations.