Screening of Saccharomyces cerevisiae and Torulaspora delbrueckii strains in relation to their effect on malolactic fermentation

Application of fixed-frequency ultrasound in the cultivation of Saccharomyces cerevisiae for rice wine fermentation

BACKGROUND

Rice wine (RW) fermentation is limited by its long fermentation time, weak taste and unpleasant flavors such as oil and odor. In this study, a novel ultrasound technology of Saccharomyces cerevisiae was used with the aim of improving fermentation efficiency and volatile flavor quality of RW.

RESULTS

The results showed that fixed-frequency ultrasonic treatment (28 kHz, 45 W L-1, 20 min) of S. cerevisiae seed culture at its logarithmic metaphase significantly increased the biomass and alcohol yield by 31.58% and 26.45%, respectively, and reduced fermentation time by nearly 2 days. Flavor analysis indicated that the flavor compounds in RW, specifically the esters and alcohols, were also increased in quantity after the ultrasonic treatment of S. cerevisiae seed liquid. Isobutyl acetate, ethyl butyrate, ethyl hexanoate and phenethyl acetate contents were increased by 78.92%, 129.19%, 7.79% and 97.84%, respectively, as compared to the control.

CONCLUSION

Ultrasonic treatment of S. cerevisiae reduced fermentation time and enhanced the flavor profile of RW. This study could provide a theoretical and/or technological basis for the research and development of RW. © 2024 Society of Chemical Industry.

Effects of Heterologous Expression of Genes Related L-Malic acid Metabolism in Saccharomyces uvarum on Flavor Substances Production in Wine

During malolactic fermentation (MLF) of vinification, the harsh L-malic acid undergoes transformation into the milder L-lactic acid, and via decarboxylation reactions it is catalyzed by malolactic enzymes in LAB. The use of bacterial malolactic starter cultures, which usually present challenges in the industry as the suboptimal conditions after alcoholic fermentation (AF), including nutrient limitations, low temperatures, acidic pH levels, elevated alcohol, and sulfur dioxide concentrations after AF, lead to "stuck" or "sluggish" MLF and spoilage of wines. Saccharomyces uvarum has interesting oenological properties and provides a stronger aromatic intensity than Saccharomyces cerevisiae in AF. In the study, the biological pathways of deacidification were constructed in S. uvarum, which made the S. uvarum carry out the AF and MLF simultaneously, as different genes encoding malolactic enzyme (mleS or mleA), malic enzyme (MAE2), and malate permease (melP or MAE1) from Schizosaccharomyces pombe, Lactococcus lactis, Oenococcus oeni, and Lactobacillus plantarum were heterologously expressed. For further inquiry, the effect of L-malic acid metabolism on the flavor balance in wine, the related flavor substances, higher alcohols, and esters production, were detected. Of all the recombinants, the strains WYm1SN with coexpression of malate permease gene MAE1 from S. pombe and malolactic enzyme gene mleS from L. lactis and WYm1m2 with coexpression of gene MAE1 and malate permease gene MAE2 from S. pombe could reduce the L-malic acid contents to about 1 g/L, and in which the mutant WYm1SN exhibited the best effect on the flavor quality improvement.

Succinic acid production by wine yeasts and the influence of GABA and glutamic acid

As a consequence of alcoholic fermentation (AF) in wine, several compounds are released by yeasts, and some of them are linked to the general quality and mouthfeel perceptions in wine. However, others, such as succinic acid, act as inhibitors, mainly of malolactic fermentation. Succinic acid is produced by non-Saccharomyces and Saccharomyces yeasts during the initial stages of AF, and the presence of some amino acids such as γ-aminobutyric acid (GABA) and glutamic acid can increase the concentration of succinic acid. However, the influence of these amino acids on succinic acid production has been studied very little to date. In this work, we studied the production of succinic acid by different strains of non-Saccharomyces and Saccharomyces yeasts during AF in synthetic must, and the influence of the addition of GABA or glutamic acid or a combination of both. The results showed that succinic acid can be produced by non-Saccharomyces yeasts with values in the range of 0.2-0.4 g/L. Moreover, the addition of GABA or glutamic acid can increase the concentration of succinic acid produced by some strains to almost 100 mg/L more than the control, while other strains produce less. Consequently, higher succinic acid production by non-Saccharomyces yeast in coinoculated fermentations with S. cerevisiae strains could represent a risk of inhibiting Oenococcus oeni and therefore the MLF.

The use of Torulaspora delbrueckii to improve malolactic fermentation

The potential use of Torulaspora delbrueckii as a starter culture for wine alcoholic fermentation has become a subject of interest in oenological research. The use of this non-Saccharomyces yeast can modulate different wine attributes, such as aromatic substances, organic acids and phenolic compound compositions. Thus, the obtained wines are different from those fermented with Saccharomyces cerevisiae as the sole starter. Nevertheless, information about the possible effects of T. delbrueckii chemical modulation on subsequent malolactic fermentation is still not fully explained. In general, T. delbrueckii is related to a decrease in toxic compounds that negatively affect Oenococcus oeni and an increase in others that are described as stimulating compounds. In this work, we aimed to compile the changes described in studies using T. delbrueckii in wine that can have a potential effect on O. oeni and highlight those works that directly evaluated O. oeni performance in T. delbrueckii fermented wines.

Comparative study of inoculation strategies of Torulaspora delbrueckii and Saccharomyces cerevisiae on the performance of alcoholic and malolactic fermentations in an optimized synthetic grape must

Progress in oenological biotechnology now makes it possible to control alcoholic (AF) and malolactic (MLF) fermentation processes for the production of wines. Key factors in controlling these processes and enhancing wine quality include the use of selected strains of non-Saccharomyces species, Saccharomyces cerevisiae, and Oenococcus oeni, as well as the method of inoculation (co-inoculation or sequential) and the timing of inoculation. In the present work, we investigated the effects of different inoculation strategies of two Torulaspora delbrueckii (Td-V and Td-P) strains followed by S. cerevisiae. Times (two, four, and six days) and types (co-inoculation and sequential) of inoculation were evaluated on the AF of a synthetic grape must. Furthermore, this synthetic medium was optimized by adding linoleic acid and β-sitosterol to simulate the natural grape must and facilitate reproducible results in potential assays. Subsequently, the wines obtained were inoculated with two strains of Oenococcus oeni to carry out MLF. Parameters after AF were analysed to observe the impact of wine composition on the MLF performance. The results showed that the optimization of the must through the addition of linoleic acid and β-sitosterol significantly enhanced MLF performance. This suggests that these lipids can positively impact the metabolism of O. oeni, leading to improved MLF efficiency. Furthermore, we observed that a 4-day contact period with T. delbrueckii leads to the most efficient MLF process and contributed to the modification of certain AF metabolites, such as the reduction of ethanol and acetic acid, as well as an increase in available nitrogen. The combination of Td-P with Oo-VP41 for 4 or 6 days during MLF showed that it could be the optimal option in terms of efficiency. By evaluating different T. delbrueckii inoculation strategies, optimizing the synthetic medium and studying the effects on wine composition, we aimed to gain insights into the relationship between AF conditions and subsequent MLF performance. Through this study, we aim to provide valuable insights for winemakers and researchers in the field of wine production and will contribute to a better understanding of the complex interactions between these species in the fermentation process.