Redox balance in wine yeast under hyperosmotic stress and the relation to wine quality

冰酒是加拿大的旗舰酒，引领了加拿大葡萄酒的国际贸易。它对加拿大葡萄酒行业仍然至关重要，2011年批准出售的冰酒价值1亿美元。生产这些葡萄酒对酿酒酵母进行发酵提出了许多挑战。冰酒汁中的溶质使酒酵母处于更高的高渗压力下，导致代谢改变，发酵困难，醋酸浓度是餐酒中的十倍。冰酒中高浓度的醋酸是一个值得关注的问题，因为它与葡萄酒变质有关。葡萄酒酵母菌株显示出与实验室研究的酵母菌株不同的特性，这些差异会影响葡萄酒的感官特性。然而，这些差异的分子基础在很大程度上仍然未知。本项目的中心研究目标是在分子水平上更全面地了解在浓缩葡萄汁发酵过程中影响葡萄酒酵母应激反应的因素，以及这些反应与细胞氧化还原平衡、甘油、有机酸生产和整体葡萄酒质量之间的关系。当酵母首先适应浓缩冰酒汁的高渗胁迫，然后在发酵过程中适应乙醇和乙酸胁迫时，我们将研究这些影响。一旦我们了解了在这种反应中形成某些代谢物的原因，就有可能控制酵母的代谢，以避免或尽量减少不需要的化合物，如乙酸。这项研究将为开发最适合冰酒和基于高糖度果汁的葡萄酒风格的酵母菌株提供关键信息，例如在新兴的加拿大appassimento葡萄酒风格中发现的由葡萄成熟的葡萄酒。这些信息将适用于酿酒师，帮助他们保持和扩大加拿大在冰酒质量方面的全球主导地位，并支持他们在涉及高糖果汁的新葡萄酒风格方面的需求。

Icewine is the flagship wine of Canada that spearheaded international trade for Canadian wines. It continues to be of critical importance to the Canadian wine industry, with Icewines approved for sale in 2011 worth $100 million. Producing these wines offers many challenges to wine yeast carrying out the fermentations. Solutes in Icewine juice place wine yeast under increased hyperosmotic stress, leading to altered metabolism, fermentation difficulties and ten-times the concentration of acetic acid found in table wines. A high concentration of acetic acid in Icewine is a concern due to its association with wine spoilage. Wine yeast strains display properties that are distinct from well-studied laboratory yeast strains, and these differences can impact on the organoleptic properties of wine. However, the molecular basis of these differences remains largely unknown. The central research goal of this program is to gain a more comprehensive understanding, at the molecular level, of factors influencing wine yeast stress responses during fermentation of concentrated grape juices and how these responses relate to cellular redox balance, glycerol, organic acid production and overall wine quality. We will examine such influences while yeast adapt first to the hyperosmotic stress from concentrated Icewine juice, and then to ethanol and acetic acid stress as fermentation proceeds. Once we understand why certain metabolites are formed during this response, it should be possible to control yeast metabolism to avoid or minimize unwanted compounds such as acetic acid. This research will provide critical information for the development of yeast strains best suited for Icewine and wine styles based on high Brix juice, such as that found in the emerging Canadian appassimento wine style produced from grapes ripened off-vine. This information will be applicable to winemakers, assisting them in maintaining and expanding Canada's global dominance in Icewine quality and supporting their needs as they branch into new wine styles involving high sugar juices.