Resveratrol and a Novel Tyrosinase in Carignan Grape Juice

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Abstract
Polyphenol levels in wines are affected by the wine-making process. Resveratrol is one polyphenol which has been the subject of a commendable amount of recent research. In this work, we found that resveratrol is immediately degraded by tyrosinase. A novel tyrosinase was purified from Carignan grapes. The purification process included salting out and separation on a cation-exchange column, followed by gel filtration. Tyrosinase was purified in a homogeneous form by SDS−PAGE and was characterized: its specific activity toward 3-(3,4-dihydroxyphenyl)-l-alanine (DOPA) increased by a factor of 24 with an overall recovery of 3% of initial activity. The apparent molecular mass of the purified tyrosinase was 40 kDa as determined by SDS−PAGE, and 42 kDa as determined by gel filtration. Its activity was optimal at pH 6 and at 25 °C. The enzyme exhibited high activity toward phenylenediamine, epicatechin, pyrogallol, DOPA, and resveratrol. Tyrosinase activity was inhibited by KCN, thiourea, and SO2. Resveratrol levels were stable following the removal of proteins from the juice, suggesting that early spraying of grapes with SO2 is an important factor affecting the final amount of resveratrol in wine. Keywords: Resveratrol; tyrosinase; wine; grape; Vitis vinifera cv. Carignan