The grape reaction product (GRP, GRP1 or 2-S-glutathionylcaftaric 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.
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^Anis Arnous; Dimitris P. Makris; Panagiotis Kefalas (2001). "Effect of Principal Polyphenolic Components in Relation to Antioxidant Characteristics of Aged Red Wines". J. Agric. Food Chem.49 (12): 5736−5742. doi:10.1021/jf010827s.
^Veronique Cheynier; Jorge M. Ricardo da Silva (1991). "Oxidation of grape procyanidins in model solutions containing trans-caffeoyltartaric acid and polyphenol oxidase". J. Agric. Food Chem.39 (6): 1047–1049. doi:10.1021/jf00006a008.
^Caftaric Acid Disappearance and Conversion to Products of Enzymic Oxidation in Grape Must and Wine. V. L. Singleton, M. Salgues, J. Zaya and E. Trousdale, Am. J. Enol. Vitic, 1985, volume 36, number 1, pages 50-56 'abstract)
^Salgues, M.; Cheynier, V.; Gunata, Z.; Wylde, R. (1986). "Oxidation of Grape Juice 2-S-Glutathionyl Caffeoyl Tartaric Acid by Botrytis cinerea Laccase and Characterization of a New Substance: 2,5-di-S-Glutathionyl Caffeoyl Tartaric Acid". Journal of Food Science51 (5): 1191. doi:10.1111/j.1365-2621.1986.tb13081.x.
^Must browning in relation to the behavior of phenolic compounds during oxidation. Cheynier V., Rigaud J., Souquet J.-M., Duprat F. and Moutounet M., American journal of enology and viticulture, 1990, vol. 41, no4. pp. 346–349, INIST:5402970.
^Véronique Cheynier; Jacques Rigaud; Michel Moutounet (1990). "Oxidation kinetics of trans-caffeoyltartrate and its glutathione derivatives in grape musts". Phytochemistry29 (6): 1751–1753. doi:10.1016/0031-9422(90)85008-4.
^Petros Kneknopoulos; George K. Skouroumounis; Yoji Hayasaka; Dennis K. Taylor (2011). "New Phenolic Grape Skin Products from Vitis vinifera cv. Pinot Noir". J. Agric. Food Chem.59 (3): 1005–1011. doi:10.1021/jf103682x. PMID21214245.