Metabolomic profiling of non-Saccharomyces yeasts in wine

[摘要] ENGLISH ABSTRACT: Recent trends in wine making have led to the commercial production and use of non-Saccharomyces yeasts in wine making. Very little is understood however about how the use ofthese yeasts affects the final product. The purpose of this study was to evaluate the chemical andsensory characteristics of wine fermented with non-Saccharomyces yeasts using a sequentialinoculation strategy. Targeted and untargeted analysis techniques were developed to help identifyand quantify the volatile fraction of the wines produced. By combining this and sensory data wewere able to build the most comprehensive picture to date of the volatile wine metabolome as it isinfluenced by various yeast species.The first step was a literature review dedicated to summarizing the current knowledgesurrounding the metabolomics of the yeasts used in the subsequent chapters. Specifically, wesought to understand what is currently known about the use of non-Saccharomyces yeasts in wine.Also investigated were the technologies currently being used in the fields of food, wine, and yeastmetabolomics. The goal was to provide the background necessary to understand the research inthe subsequent chapters, as well as aid in the development and planning of the experimentsdiscussed here within.Two stages of research were conducted. Not only did we want to understand the effects ofnon-Saccharomyces yeasts on wine aroma but we were interested in whether or not these effectswere the same in both red and white wines. As such the first research stage, was a preliminaryinvestigation of the yeast response to two different grape musts. Five different species of non-Saccharomyces yeasts, were chosen and grown in both Shiraz and Sauvignon blanc must andsamples were collected for analysis just prior to the point at which Saccharomyces cerevisiaewould usually be added to complete the fermentation. The fermentation rates were monitored andthe chemical profile of the musts was evaluated. A solid-phase microextraction-GasChromatography-Mass spectrometry method that targeted 90 different compounds known to befound in wine was used to evaluate the headspace of the fermented musts.The results obtained helped shape the experimental design for the next phase of the project.The scale was increased to full wine production to evaluate how the yeasts could influence acompleted wine product. Again, Sauvignon blanc and Shiraz were chosen and an untargetedchemical analysis method was developed to ensure that the widest possible range of analytescould be evaluated. The finished Sauvignon blanc wine was also subjected to sensory analysiswhich provided even greater insight into how these inoculation strategies can change the sensoryprofile of the wine.This research was undertaken in an attempt to answer the questions of 'What will the winesmell and taste like if I use non-Saccharomyces yeasts during fermentation?' and 'Could it besuperior to standard wines only inoculated with S. cerevisiae?' The experiments conductedprovided a great deal of insight that can help to begin answering these questions but there is muchthat remains unknown. In general, we were able to build a detailed volatiles chemical profile foreach of the yeast treatments used in both Shiraz and Sauvignon blanc. While some treatmentsproved to be somewhat detrimental to the aroma and flavor of the wine, others showed promise inpossibly enhancing its complexity. We were also able to demonstrate that the yeasts behave verydifferently in the two different musts. As comprehensive as these studies were, future work shouldbe undertaken to improve the understanding of why and how these yeasts can make an impact onwine production. For example, our work did not include any genetic expression analysis of theyeasts used. Correlating genetic expression to quantitative chemical analysis would provide amuch more complete picture of the wine yeast metabolome.

[发布机构] Stellenbosch University