Grape reaction product
Grape reaction product (GRP) is a chemical formed from caftaric acid during grape processing. It is also known as GRP1 or 2-S-glutathionyl caftaric acid.
How it forms and why it matters:
GRP forms mainly through the action of polyphenol oxidase enzymes. It helps limit browning of grape musts, which is especially important when white wine is being produced.
Where it is found:
GRP is present in grapes and can be found in aged red wines.
Laboratory use and measurement:
GRP can be recreated in model solutions in the lab. Its amount in wine can be determined using mass spectrometry. GRP itself can be oxidized.
Reactivity and related compounds:
GRP is not a substrate for grape polyphenol oxidase, but laccase enzymes from Botrytis cinerea can convert it into a related compound called GRP2. Related molecules include GRP o-quinone, GRP2, and adducts with anthocyanidins.
This page was last edited on 3 February 2026, at 02:41 (CET).