Rapid Analysis for Available Nitrogen Compounds in Must
A rapid method for the analysis of a-amino acids in must would help winemakers decide in a timely manner whether or not they should supplement nitrogen levels prior to fermentation. Inadequate nitrogen levels can lead to sluggish or stuck fermentations, while excessive nitrogen levels can lead to the formation of ethyl carbamate. Our findings have demonstrated that the concentration of ammonia in the must is not correlated with the concentration of a-amino acids (r2=0.202, N=35) in juices from the 1994 vintage. Thus, ammonia determinations can not be used as a rational indication for the nutritional status of grape juice. The requirement for the determination of a-amino acid concentration (as well as ammonia concentration) has thus been demonstrated. We developed and tested a new assay for analysis of nitrogen in grape must. It is based on photometric determination of amino acids as o-phthalaldehyde (OPA), N-acetyl-L-cysteine (NAC) derivatives. Our results show the test’s advantages over conventional and alternative nitrogen assays used in the wine industry. The test shows reasonable correlation with standard HPLC analysis. The main focus of research is currently fine tuning of the procedure to reduce error. It is insensitive to proline, the most abundant yet for wine yeast not utilizable amino acid in must. It is extremely rapid, works at room temperature, and uses stable and non-toxic reagents. At ‘ present the assay shows reasonable correlation (r2=0.818) with standard HPLC analysis. The findings from our first 6 months suggest that the optimization of the test will be completed by August 1995. Our current focus of research is to increase performance of this assay and to simplify our procedure, to make the test available for industrial application in the 1995 crush.