Evolução aromática e autofagia/autólise durante a segunda fermentação de espumantes

Abstract

The Serra Gaucha region shows an excellent oenological aptitude for the production of high quality wines and sparkling wines. Sparkling wines process involves a second fermentation with gas and ethanol production, and several biological and chemical transformations that influence the organoleptic properties of the final product. After the second fermentation sparkling wines mature in contact with the lees (sur lie) for long periods during which yeasts autophagy/autolysis occurs. In this work we evaluate the physic-chemical characteristics and volatile compounds during the second fermentation and maturation of sparkling wines, as well as the dynamics of yeast population and the expression of autophagic/autolytic related genes. For this purpose second fermentations were conducted by the traditional method using a base wine elaborated with Pinot Noir, Chardonnay and Riesling Italic and the S. cerevisiae EC1118 commercial strain. Samples were collected at 0, 7, 15, 30, 60, 90, 135, 180, 270 and 360 days of fermentation, and evaluated with respect to the basic physic-chemical characteristics, volatile compounds (27 compounds), yeast population, and the concentration of phenolic compounds and protein/peptides. The expression of autophagy/autolysis related genes during the second fermentation and the beginning of maturation was determined by qRT-PCR. The results showed that the second fermentation involved an initial adaptation period of 7 days followed by an important increment in the alcoholic concentration during 30 days. During the fermentation and maturation it was observed a reduction in total acidity and a small increase of volatile acidity that led to a pH increase in the final product. A significant variation in several volatile compounds was detected during second fermentation and maturation of sparkling wines, with a reduction in esters after 90 days. Multivariate analysis showed that sparkling wines suffer important modifications during second fermentation. After 270 days of maturation sparkling wines exhibited a reduction in the concentration of 1-propanol, 2-methyl-1-buthanol, 3- methyl-1-buthanol, ethyl octanoate, decanoic acid, and dodecanoic acid, and an increase in the concentration of diethyl succinate, ethyl dodecanoate and phenylethanol. Increase in the concentration of phenolic compounds during maturation, can affect wine color. Yeast population (UFC/mL) exhibited an important increase during the fermentation period followed by a drastic reduction (~80%) in the next 30 days. However, the total number of cells remained constant between 30 and 90 days, a rapidly decrease after this period indicating yeast autolysis. The reduction of yeast cells was accompanied by an increase in the concentration of proteins/peptides in wine, which stabilized at 270 days. The evaluation of expression of a group of genes related with the autophagic process indicated that both micro and macroautophagy are induced during the second fermentation with an increase of macroautophagy at the end of the fermentation period, accompanying the decrease in yeast viability.