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

Int J Biol Macromol. 2021 Feb 15:170:261-271. doi: 10.1016/j.ijbiomac.2020.12.147. Epub 2020 Dec 24.


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 °C, while the optimum pH value varied from 5.0 to 7.0 depending on the substrate. The kcat/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, β-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.

Keywords: Enzyme characterization; Enzyme inhibition; Enzyme purification; Fennel seeds; Organic solvents; Polyphenol oxidase.

MeSH terms

  • Ascorbic Acid / pharmacology
  • Catechol Oxidase / chemistry*
  • Catechol Oxidase / isolation & purification*
  • Catechols
  • Foeniculum / chemistry*
  • Foeniculum / metabolism
  • Fruit / chemistry
  • Fruit / enzymology
  • Hydrogen-Ion Concentration
  • Kinetics
  • Molecular Weight
  • Oxidation-Reduction
  • Pyrogallol
  • Seeds / chemistry
  • Substrate Specificity
  • Sulfites
  • Temperature


  • Catechols
  • Sulfites
  • Pyrogallol
  • 4-methylcatechol
  • sodium metabisulfite
  • p-tert-butyl catechol
  • Catechol Oxidase
  • catechol
  • Ascorbic Acid