Wine Analysis Home

Tyrosinase

• Tyrosinase is a grape derived, oxidative enzyme.
  
  
• Synonyms for Tyrosinase are polyphenoloxidase, catecholoxidase, catecholase, phenolase, phenoloxidase and
  o-diphenoloxidase.
  
  
• Tyrosinase is located in the chloroplasts of the grape berry and hence forms part of the grape berry's cell membrane system and in juice prdominantly exists attached to grape particles. Hence, the juice enzyme (tyrosinase) concentration can be reduced substantially by settling and juice clarification.
  
  
• The enzyme tyrosinase is particularly sensitive to sulphur dioxide (SO₂) and will inhibit or denature the enzyme and hence reduce grape juice oxidation.
  
  
• It functions at its optimum between pH 4-5.
  
  
• Hence, at juice/wine pH values of 3.0-4.0 it looses its activity with time and will be totally inactive in wine, unlike the enzyme laccase, introduce through botrytise infection of the grape berry, which will persist through to the wine.