Search

Background (1): The use of fungal chitosan as an antiseptic in wine appears as a promising alternative to sulfur dioxide for the elimination of Brettanomyces bruxellensis sensitive strains. Nevertheless, its utilization raises the question, “how are the treated wines different from the untreated ones?” Methods (2): Chitosan treatment residues were sought in the oligosaccharide and polysaccharide fractions and among 224 low MW ions (−1) in several wines by using liquid chromatography (size exclusion HPLC or LC-MS) and GC-MS. Standard oenological parameters were also examined as well as possible sensory modifications by a panel of tasters composed of experts and non-experts. Results (3): None of these methods enabled the reproducible and reliable identification of a treated wine without comparing it to its untreated control. The fingerprints of treatment are not reliably detectable by the analytical methods used in this study. However, the treated wines seem permanently protected against the development of chitosan-sensitive strains of B. bruxellensis. Conclusions (4): If chitosan treatment modifies the wine, the associated changes were not identified by the liquid chromatography method mentioned above and they were not perceived by most people in our taster panel. However, the expected antimicrobial action of chitosan was observed on B. bruxellensis sensitive strains and persisted at least one year. Tolerant strains were less affected by these persistent effects.

Lactic acid bacteria (LAB) are Gram positive bacteria frequently used in the food industry for fermentation, mainly transformation of carbohydrates into lactic acid. In addition, these bacteria also have the capacity to metabolize citrate, an organic acid commonly found in food products. Its fermentation leads to the production of 4-carbon compounds such as diacetyl, resulting in a buttery flavor desired in dairy products. Citrate metabolism is known to have several beneficial effects on LAB physiology. Nevertheless, a controversial effect of citrate has been described on the acid tolerance of the wine bacterium Oenococcus oeni. This observation raises questions about the effect of citrate on the capacity of O. oeni to conduct malolactic fermentation in highly acidic wines. This review aims to summarize the current understanding of citrate metabolism in LAB, with a focus on the wine bacterium O. oeni. Metabolism with the related enzymes is detailed, as are the involved genes organized in cit loci. The known systems of cit locus expression regulation are also described. Finally, the beneficial effects of citrate catabolism on LAB physiology are reported and the negative impact observed in O. oeni is discussed.

Assyrtiko is a rare ancient grape variety of Greece, which is known to produce Protected Designation of Origin (PDO) Santorini white wines. Besides the famous character of the volcanic terroir, Assyrtiko of Santorini is also marked by a low pH value and sharp acidity. The aim of the present study was to apply a new inoculation procedure that modulates the fermentation process by maintaining the unique sensorial characteristics of Assyrtiko wines based on acidity. For this purpose, the Lachancea thermotolerans species, known for the formation of lactic acid, was tested in sequential fermentation with three different Saccharomyces cerevisiae strains. At the end of the fermentation process, implantation control for S. cerevisiae strains (interdelta sequence profile analysis) was performed, oenological parameters were determined according to the OIV protocols, and the volatile compounds produced were measured by gas chromatography–mass spectrometry (GC/MS). Finally, all produced wines were evaluated by quantitative descriptive analysis by two groups of experts; the Greek team of oenologists from Santorini Island specialized in Assyrtiko wines, and the French team of oenologists specialized in wine from Bordeaux. As expected, the inoculated strain was the one that dominated the fermentation process, but nine S. cerevisiae indigenous strains were also identified in the produced wines. Lachancea thermotolerans produced 1 g/L of lactic and also modulated the volatile profile of the wines independently of the S. cerevisiae strain used. The origin of the panelists played an important role in bringing up sensorial traits, such as acidity. Our results led to a new interesting application of L. thermotolerans for white wine production adapted to climate change claims.

Additives have been used in the food industry for many years, to prevent food spoilage and extend shelf life. These chemical additives are a source of controversy and their use must be reduced in the face of societal demand. In enology, this applies in particular to sulfur dioxide (SO2). There has been recent research on bioprotection as an alternative to sulfite addition in the pre-fermentation phase. This technical article discusses the many advantages of using bioprotection agents.

As part of the move to reduce SO2 in wines, the empirical use of chitosan to eliminate the spoilage yeast Brettanomyces bruxellensis is becoming a frequent alternative. Chitosan treatment has an effect on a number of microbial species, at least temporarily, but there is wide variability in response within strains of each species. In addition, the effectiveness of chitosan also depends on the physical and chemical parameters of the wine. However, when chitosan treatment is effective, it appears to be long-lasting.

The use of multi-starters in oenological conditions (Saccharomyces cerevisiae and non-Saccharomyces species) is becoming increasingly common. For the past ten years, the combination of Torulaspora delbrueckii and S. cerevisiae has been proposed to winemakers to improve the wine aromatic profile compared to pure inoculation with Saccharomyces cerevisiae. In this work, two commercial strains, T. delbrueckii Zymaflore® Alpha and S. cerevisiae Zymaflore® X5 (Laffort compagny, Floirac, France), were investigated in Sauvignon blanc must using a fermentor with a double compartment allowing for physical separation of the two yeast species. The physical separation of the two species resulted in significant differences in the growth, fermentation kinetics (maximum fermentation rate (+13%)), fermentation duration (−14%) and the production of 3SH (+35%) in comparison to mixed cultures with contact. Proteomic analysis confirmed cell–cell contact interactions, as strong differences were observed for both species between mixed cultures with and without physical contact. T. delbrueckii mortality in mixed cultures with physical contact may be explained by an oxidative stress. Indeed two proteins implicated in the oxidative stress response were found in significantly higher amounts: a cytosolic catalase T and a cytoplasmic thioredoxin isoenzyme. For S. cerevisiae, an increase in proteins involved in the respiratory chain and proton transport were found in higher amounts in pure cultures and mixed culture without physical contact. Our results confirmed that the two mixed inoculations increased certain minor esters (ethylpropanoate, ethyl dihydrocinnamate and ethyl isobutanoate) specifically produced by T. delbrueckii, 3.4-fold more compared to in the pure S. cerevisiae culture. In conclusion, these results provide new insights into the underlying mechanisms involved in cell–cell contact and confirm the benefits of using T. delbrueckii species under winemaking conditions.

Viognier is a warm climate grape variety prone to loss of acidity and accumulation of excessive sugars. The yeast Lachancea thermotolerans can improve the stability and balance of such wines due to the partial conversion of sugars to lactic acid during alcoholic fermentation. This study compared the performance of five L. thermotolerans strains in co-inoculations and sequential inoculations with Saccharomyces cerevisiae in high sugar/pH Viognier fermentations. The results highlighted the dichotomy between the non-acidified and the bio-acidified L. thermotolerans treatments, with either comparable or up to 0.5 units lower pH relative to the S. cerevisiae control. Significant differences were detected in a range of flavour-active yeast volatile metabolites. The perceived acidity mirrored the modulations in wine pH/TA, as confirmed via “Rate-All-That-Apply” sensory analysis. Despite major variations in the volatile composition and acidity alike, the varietal aromatic expression (i.e., stone fruit aroma/flavour) remained conserved between the treatments.