Browsing by Author "Kelly, Molly Kathleen"

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    Effect of Foliar Nitrogen and Sulfur Applications on Aroma Profile of Vitis vinifera L. cv. Petit Manseng using Modified Quantitative Descriptive Analysis, SPME GC-MS and Electronic Nose Technology
    Kelly, Molly Kathleen (Virginia Tech, 2013-06-12)
    Petit Manseng grapes harvested in 2011 and 2012 were fertilized with soil nitrogen at 0, and 30 kgN/ha, foliar nitrogen at 15kg/ha and foliar nitrogen plus sulfur at 15kg/ha and 5kg respectively. Point quadrat analysis demonstrated foliar nitrogen alone and nitrogen plus sulfur treatments increased percent gaps and lower leaf layer numbers. Berry juice samples differed in ammonia, arginine and yeast assimilable nitrogen concentration. Total glycosides were 25 percent higher in the foliar nitrogen treatment versus the control treatment. Electronic nose measurements on field clusters and laboratory berry analyses was different among treatments in volatile content. Harvest samples underwent acid or enzyme hydrolysis of precursor fractions. Solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC/MS) analysis identified 27 free aroma and flavor compounds and 52 bound compounds. Lactones and carboxylic acids were the major components of the free fractions while bound fractions had increased concentrations of alcohols, esters and terpenes compared to the free fraction. With nitrogen fertilization, acid and enzyme hydrolysis had reduced concentrations of some higher alcohols and carboxylic acids. Acid hydrolysis released more terpenes with nitrogen treatments versus enzymatic hydrolysis. Ester content was increased in both acid and enzyme hydrolysis fractions in vines receiving nitrogen treatments. For descriptive analysis, eight trained panelists described aroma, flavor, texture/mouthfeel and aftertaste attributes. Analysis of Variance (ANOVA) demonstrated that wines were a significant source of variation with 23 of the 24 attributes used. Wine principal component analysis (PCA) of aroma attributes explained 23.5% of the variation from PC1, while flavor-by-mouth and texture/mouthfeel attributes explained 26.3% of the variation due to PC1. The aim of this study was to develop descriptive terms for Petit Manseng and determine the influence of fruit nitrogen levels on the aroma and flavor profile of this cultivar.
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    Refining Fruit-Zone Leaf Removal for Red-Fruited Bordeaux Grape Varieties Grown in a Humid Environment
    Hickey, Cain C. (Virginia Tech, 2016-06-30)
    Current fruit-zone management recommendation in the eastern US aims for 1-2 basal shoot leaf layers after fruit set to limit fungal disease and sunburn incidence, and prevent extreme heating of grapes. The goal of this work was to assess if fruit-zone leaf removal to an uncommonly greater extent, and/or at an earlier phenological stage, would favorably alter yield components or fruit composition in three popularly grown, red-fruited, Bordeaux varieties – Cabernet franc, Petit Verdot, and Cabernet Sauvignon. Pre-bloom leaf removal to various extents reduced crop yield by 41-78% when compared to no leaf removal across seasons and varieties. Pre-bloom leaf removal implementation in consecutive seasons tended to further reduce crop yield components compared to implementation in the first year. Pre-bloom leaf removal tended to reduce cluster compactness and bunch rot incidence when compared to post-fruit set and no leaf removal. Basal leaf removal to the greatest extents inconsistently reduced soluble solids and titratable acidity across varieties and seasons. Pre-bloom and post-fruit set leaf removal to the greatest extent consistently increased total grape phenolics and anthocyanins compared to no leaf removal in Cabernet Sauvignon, but inconsistently increased total grape phenolics compared to no leaf removal in Cabernet franc and Petit Verdot. Basal leaf removal to the greatest extents tended to increase the synthesis and degradation of carotenoids more consistently than no leaf removal, and this was particularly true for zeaxanthin. Petit Verdot and Cabernet franc wine color and aroma were inconsistently distinguishable between leaf removal treatments, and color intensity was rated higher in wines made with fruit from pre-bloom leaf removal compared to modest post fruit-set leaf removal plots. Waiting until after fruit set to remove fruit-zone leaves maintained crop yield and offered comparable improvements in fruit composition to pre-bloom leaf removal. Pre-bloom leaf removal of no more than four leaves is recommended to limit crop yield reduction, and modestly improve fruit composition. This work showed that fruit-zone leaf removal does not need to be conservative in the eastern US, particularly because the climate does not appear to be detrimental to fruit composition, and open fruit-zones reduce grape fungal disease incidence.