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Interfering substances in the colorimetric quantitation of grape monoterpenes

, : Interfering substances in the colorimetric quantitation of grape monoterpenes. Hortscience 29(11): 1335-1336

The potential for interference by specific C-6 compounds in the colorimetric quantitation of grape (Vitis vinifera L.) monoterpenes was investigated in model solutions and muscat and neutral-flavored grape cultivars. The unsaturated C-6 aldehyde 2hexen-1-al (2HX) showed color absorption at 608 nm in distilled water after reaction with an acidified vanillin solution. Absorbance also increased significantly when 2HX was added to a series of linalool solutions; apprxeq 2.5 mg 2HX per liter of a 1-mg.liter-1 linalool solution increased the absorbance by gt 10%. Adding 2.5 mg 2HX per kilogram of 'Gewurztraminer' berry homogenate significantly increased apparent free volatile terpene (FVT) concentrations to 121% of unadulterated control treatments but did not affect potentially volatile terpenes (PVT). Adding 2HX also increased apparent FVT concentration in 'Perlette' and 'Flame Seedless'. Both neutral-flavored table grape cultivars contained some FVT and PVT as a consequence of their muscat ancestries. FVT and PVT quantitation by colorimetric methods may be subject to significant error if the concentration of 2HX and other unsaturated C-6 compounds in grape berries or must are gt 5 mg.liter-1. However, low concentrations of unsaturated C-6 compounds ( lt 80 mu-g.liter-1) in British Columbia wines suggest that there is a low probability of significant interference with this method.


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