Spectrophotometric assay for arginine in grape juice and must

An assay for arginine was developed that involves its separation from other amino acids by cation exchange followed by a spectrophotometric quantification as an o-phthaldialdehyde/n-acetyl-L-cysteine derivative. Arginine is usually the most abundant yeast assimilable amino acid in grape juice and must, and a natural precursor to ethyl carbamate (EC) formation in wine. Ethyl carbamate is a naturally occurring component of all fermented foods and beverages. Because EC has shown a potential for carcinogenicity when administered in high doses in animal tests, the wine industry is interested in reducing EC levels in their products. Elevated arginine concentrations in grape juice and must can lead to a increased potential for EC concentrations in wine. The arginine molecule has an isoelectric point above all other amino acids relevant to grape juice and wine. The assay uses a strong cation exchange cartridge to isolate arginine from all other amino acids in grape juice, and a modified version of a previously published spectrophotometric assay for yeast assimilable amino acids to measure the isolated arginine. The effects of potential grape juice-specific interferences in both model solutions and real musts were investigated and eliminated. The method was validated by determination of linear response to known standards, recovery of spiked samples and correlation to a reference method (R-2 = 0.987). In addition to its accuracy and speed, the method, termed ARGOPA for "arginine by o-phthaldialdehyde", is robust, simple and inexpensive enough to be used under commercial winemaking conditions. A winery laboratory procedure for the assay can be downloaded at < http://wineserver.ucdavis.edu/oldsite/argopa99.pdf >.