One of the challenges facing wine growers is that grapes have high polyphenol oxidase (PPO) activity.  This natural enzyme contributes to the rate of browning in the fruit after it is picked.  Browning causes a change in color and flavor of the juice, and diminishes the quality of the final product.  Thus, scientists have worked for years to understand the factors regulating PPO levels in grapes.

It is known that the application of chemical pesticides and fertilizers can affect the levels of phenolics in plants.   A study by a team of Spanish scientists was designed to explore the impacts of pesticides and fertilization methods on PPO levels in organically and conventionally grown Monastrell wine grapes.

The key finding of this study is that PPO activity in organic grapes was found to be twice that of conventionally grown grapes.   This higher PPO activity “could be the result of changes in phenolic metabolism in plants grown in the absence of synthetic pesticides and most of the readily soluble mineral fertilizers…This increase in PPO activity may contribute effectively to disease resistance in organic farming via rapid oxidation of phenols to quinines, thus inhibiting the polygalacturonase of pathogens.”  It might also contribute to higher levels of stilbenes, antioxidants known to determine the flavor profile of a given wine.

Additional implications of this study include that PPO can be considered a marker for differentiating organic versus conventionally grown grapes.  Also, “wines obtained from organic grapes could be more oxidated than those obtained from conventional grapes.”

Source:  “Effect of organic farming practices on the level of latent polyphenol oxidase in grapes.”

Auihors: Estrella Núñez-Delicado, Alvaro Sánchez-Ferrer, Francisco F. García-Carmona, and Jose Manuel López- Nicolás, Journal of Food Science, Volume 70, Number 1, January 2005.