Formula C23H27N3O15S | Molar mass 617.53 g/mol | |
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The grape reaction product (GRP, GRP1 or 2-S-glutathionyl caftaric acid) is a phenolic compound explaining the disappearance of caftaric acid from grape must during processing. It is also found in aged red wines. Its enzymatic production by polyphenol oxidase is important in limiting the browning of musts, especially in white wine production. The product can be recreated in model solutions.
It is possible to determine its concentration in wine by mass spectrometry.
S-Glutathionyl caftaric acid is itself oxidizable. It is not a substrate for grape polyphenol oxidase, but laccase from Botrytis cinerea can use it to form GRP2.
Related molecules
Other related molecules are trans-caffeoyltartrate derivatives like GRP o-quinone and 2,5-di-S-glutathionyl cafteoyl tartrate (GRP2) or adducts with anthocyanidins.