Nitrogen composition of interspecific hybrid and Vitis vinifera wine grapes from the Eastern United States
Interspecific hybrid and native American wine grapes are grown in the Eastern United States due to challenges such as diseases, pests, and abiotic stress often precluding cultivation of the "European" grape species Vitis vinifera in this region. Vitis vinifera varieties account for some 90% of the world's grape production and most enology and viticulture research has focused on Vitis vinifera varieties. This dissertation characterizes the nitrogen concentration and composition found in interspecific hybrid and native American wine grape varieties grown in the Eastern United States. A survey of yeast assimilable nitrogen (YAN), which is essential for fermentation of grapes into wine, was made including 147 grape varieties from 12 states in four vintages from 2009 to 2012. YAN values ranged from 8 mg/L to 938 mg/L, with 19 of the 20 highest YAN values being found in extremely cold-hardy hybrid varieties developed by the University of Minnesota. Commercially available yeast nutrient supplements were evaluated to determine their YAN contribution as compared to supplier-stated YAN contributions and concentration of ammonium ions vs. α-amino nitrogen. Residual YAN in commercial wines, i.e. post-fermentation, was determined for a wide range of wines from across North America. The highest residual YAN, on average, was found in wines made from interspecific hybrids. 28 grape varieties were sampled in two vintages to determine amino acid profiles of interspecific hybrid and native American wine grape varieties. We found that proline and arginine are not the most prevalent amino acids in many of these varieties, as they are in Vitis vinifera. Finally, total phenolics and total anthocyanins were determined in red wines made from both Vitis vinifera and interspecific hybrids and aged Purdue University's research wine library including vintages from 2004 to 2012. These results provide wine-specific background information for future studies pertaining to human health and nutrition. This work provides information on fundamental differences in nitrogen concentration and composition between interspecific hybrids and Vitis vinifera. This information provides a basis for future work investigating the impact of nitrogen composition and concentration of interspecific hybrid and native American wine grapes on fermentation and flavor.
Butzke, Purdue University.
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