Amino acids as modulators of the production of hydrogen sulfide in problematic wine fermentations.

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2019
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All stages of winemaking can present problems, but alcoholic fermentation is, in particular, the stage with most complications. During wine fermentation some conditions can result in sluggish or stuck fermentations. The information provided by routine measurements has not been sufficient to detect and diagnose the state of the fermentation, and in case of paralization, rescue it on time. Hence, real-time monitoring of key variables, using advanced instrumentation, would anticipate problematic situations. Nitrogen is one of the most studied variables for sluggish or stuck fermentations. However, only a fraction of the available nitrogen is assimilated by the yeasts, constituted by ammonium ions and free α-amino acids. Nitrogen compounds have also been associated to be key factors in volatile compounds formation, including hydrogen sulfide (H2S). Sulfide release during winemaking is a longstanding and serious problem. H2S is a malodorous compound with a low sensory threshold. It’s produced as metabolic requirement of yeast for synthesizing sulphur compounds. Its formation is carried out by the sulfate reduction pathway starting from organic and inorganic sources, such as sulfites, cysteine, and glutathione. The role of amino acids and ammonium on H2S formation has shown a high variability. Individual yeast nitrogen requirements, as well as its assimilation capacity of nitrogen compounds, together with the time nitrogen is supplemented during fermentation, are oenological factors that influence sulfide formation. Furthermore, yeast variability in sulfide metabolic regulation has also a major impact on H2S formation. Genetic variability, in the form of differential allelic expression controlling sulfide reduction pathway or adjacent routes, has been found to be a decisive trait that affects yeast capacity to produce H2S. However, this information hasn’t been able to help predict and control sulfide formation through alcoholic fermentation. Considering the above, in this research nitrogen, specifically its organic sources, is studied, as regulator of H2S formation. For this, the evolution of amino acids profile during wine fermentation of Cabernet Sauvignon must was measured. Two problematic fermentations conditions were evaluated, high initial sugar concentration and low initial assimilable nitrogen content, besides the standard winery condition, with four commercial wine yeast. Samples were collected at 24 hours intervals until the maximum amount of H2S was produced. Amino acids were evaluated by HPLC (High Performance Liquid Chromatography), allowing their quantification. A colorimetric method was exclusively developed to accurately quantify H2S production. Depending on the initial condition of the fermentation some amino acid showed a characteristic evolution profile, distinctive to each yeast. Most importantly, a unique H2S release patron was established for each wine yeast in relation to the starting conditions of the must fermentation.
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Tesis (Doctor en Ciencias de la Agricultura)--Pontificia Universidad Católica de Chile, 2019
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