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Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/22/2009 Publication Date: 3/15/2010 Citation: Lee, J., Schreiner, R.P. 2010. Free amino acid profiles from 'Pinot noir' grapes are influenced by vine N-status and sample preparation method. Food Chemistry. 119:484-489. Interpretive Summary: Certain grape nitrogen (N) compounds are essential for a healthy fermentation. This study explored how altered vine nutrient regimes and sample preparation methods influenced 'Pinot noir' grape N content and composition. Technical Abstract: This study examined the impact of extraction method on ammonia, free amino acids, and YAN (yeast assimilable nitrogen) concentrations in 'Pinot noir' berries obtained from a vine nutrition study (altered supply of N, P, or K). Berries were either juiced or exhaustively extracted as whole berries prior to analysis. Extracts, compared to juice samples, had a significantly higher level of ammonia-N, assimilable amino acid-N and YAN. For example, juice YAN values were approximately 50% of extract YAN values, when both were expressed in the same units. Free amino acid profiles and relative concentrations of individual amino acids were different in juice versus extracts, depending on the how well the skin fraction was extracted prior to analysis. Lowering N supply reduced free amino acids, with arginine being reduced more than the other 20 free amino acids identified in 'Pinot noir' berries. This was true in both juice and extracts. Since berry skin contributed to actual YAN, wineries that determine YAN from mainly the pulp fraction (juice) may underestimate YAN and as a result add more (artificial) N supplement than is required for the healthy fermentation of red winemaking (whole berry fermentations). Extraction procedure should be taken into consideration when comparing grape YAN. |
