Co-Existence of Inoculated Yeast and Lactic Acid Bacteria and Their Impact on the Aroma Profile and Sensory Traits of Tempranillo Red Wine

This study investigates the effects of simultaneous inoculation of a selected Saccharomyces cerevisiae yeast strain with two different commercial strains of wine bacteria Oenococcus oeni at the beginning of the alcoholic fermentation on the kinetics of malolactic fermentation (MLF), wine chemical composition, and organoleptic characteristics in comparison with spontaneous MLF in Tempranillo grape must from Castilla-La Mancha (Spain). Evolution of MLF was assessed by the periodic analysis of L-malic acid through the enzymatic method, and most common physiochemical parameters and sensory traits were evaluated using a standardized sensory analysis. The samples were analyzed by GC/MS in SCAN mode using a Trace GC gas chromatograph and a DSQII quadrupole mass analyzer. Co-inoculation reduced the overall fermentation time by up to 2 weeks leading to a lower increase in volatile acidity. The fermentation-derived wine volatiles profile was distinct between the co-inoculated wines and spontaneous MLF and was influenced by the selected wine bacteria used in co-inoculation. Co-inoculation allows MLF to develop under reductive conditions and results in wines with very few lactic and buttery flavors, which is related to the impact of specific compounds like 2,3-butanedione. This compound has been also confirmed as being dependent on the wine bacteria use

Improving an Industrial Sherry Base Wine by Yeast Enhancement Strategies

There is growing interest in yeast selection for industrial fermentation applications since it is a factor that protects a wine's identity. Although it is strenuous evaluating the oenological characteristics of yeasts in selection processes, in many cases the most riveting yeasts produce some undesirable organoleptic characteristics in wine. The aim of the present work is to improve an industrial yeast strain by reducing its hydrogen sulfide (H2S) production. To accomplish this, two different improvement approaches were used on said yeast: hybridization by mass mating and adaptive laboratory evolution, both performed through spore generation and conjugation, thus increasing genetic variability. Three evolved variants with lower H2S production were obtained and used as starters to carry out fermentation at an industrial level. Wine quality was analyzed by its principal oenological parameters and volatile aroma compounds, which were both corroborated by sensory evaluations. Significant differences between the produced wines have been obtained and a substantial improvement in aromatic quality has been achieved. Both hybrids were the most different to the control due to terpenes and esters production, while the evolved strain was very similar to the parental strain. Not only have organoleptic defects been reduced at an industrial level, more floral and fruitier wines have been produced.This research was funded by the Centre for the Development of Industrial Technology (CDTI) (grant number IDI-20141202) and the European Regional Development Fund (ERDF) (grant number FEDER-UCA18-106947)

Evolved Saccharomyces cerevisiae strains to reduce ethyl carbamate in Sherry wines

Urea is the main precursor of ethyl carbamate in fortified wines, which is in turn mostly produced by Saccharomyces cerevisiae due to the arginine catabolism during alcoholic fermentation. Due to its potential safety risks, efforts have been taken to reduce ethyl carbamate content by reducing the urea produced. However, most of them have been made through genetic manipulation, and their use in the food industry is therefore limited by legal constraints. In the present study, the adaptive laboratory evolution technique had been used to improve this trait in a diploid wine yeast already used at industrial level to obtain Sherry base wine. For this purpose, the genetic variability of the yeast population was increased by sexual reproduction and subsequently canavanine, a toxic arginine analogue, was applied as selective pressure to select yeast variants with lower urea production. Finally, an evolved variant that showed 62% lower urea content than the parental strain, also displaying an enhanced fermentative performance, was selected. The base Sherry wine obtained at industrial level not only showed a lower urea and ethyl carbamate content, but also an improvement in the aromatic profile, being fruitier and fresher than that obtained with the parental strain mainly due to an increase in ester content

Flavanol Glycoside Content of Grape Seeds and Skins of Vitis vinifera Varieties Grown in Castilla-La Mancha, Spain

Glycosylated flavanols (monoglycosides and diglycosides) in skin and seed extracts of Vitis vinifera grapes grown in Castilla-La Mancha (Spain) were investigated using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-ESI-QQQ-MS/MS). Six grape varieties (Airen, Tempranillo, the recently identified Albillo Dorado, Montonera del Casar, Moribel, and Tinto Fragoso) were studied over two consecutive years (2016 and 2017). A total of twenty monomeric flavanol monoglycosides, four diglycosylated monomers, and three dimeric flavanol monoglycosides were detected in all grape samples. The diversity observed in the composition of glycosylated flavanol in the grape berries suggests a strong influence of variety and grape tissue (skin or seed). Monomeric flavanol glycosides were more abundant in grape seed extracts, in contrast with monoglycosylated dimeric forms. In addition, the glycosylated flavanol content was related to berry color in grape skins, with higher concentrations measured in black grape varieties