Influence of temperature and pH on S. bayanus var. uvarum growth; impact of a wine yeast interspecific hybridization on these parameters

The species Saccharomyces bayanus var. uvarum possesses interesting enological characteristics but produces high concentration of volatile fermentative compounds not desirable in Sauvignon blanc wines. Interspecific hybrids between Saccharomyces cerevisiae and S. bayanus var. uvarum were made in order to join the main parental advantages. Two hybrids were selected on the basis of their fermentation characteristics and their karyotypes, i.e. they have a different mitochondrial DNA. In order to produce these hybrids as active dry yeast to be used as starter in winemaking, their optimal environmental conditions for growth, i.e. temperature and pH, were determined as the objective of our work. Using a two-level factorial design it was found that the two parental strains have different optimal temperature but for the two strains, pH does not have a significant influence on growth. The influence of temperature on biomass productivity for hybrid strains were strictly identical, so we suppose that the main genes coding for temperature sensitivity were not contained in mitochondrial DNA, but in nuclear DNA. Moreover the reactions of hybrid strains to the temperature variations were similar to the one of S. bayanus var.uvarum. This latter strain could have a majority of genes responsible of temperature sensitivity dominant in comparison with those of the strain S. cerevisiae

Effect of ammonium concentration on alcoholic fermentation kinetics by wine yeasts for high sugar content

Kinetics of alcoholic fermentation by Saccharomyces cerevisiae wine strains in a synthetic medium with high sugar content were established for different nitrogen initial content and are presented for 4 strains. The composition of the medium was close to grape must except that the nitrogen source consisted mainly in ammonium and was varied from 120 to 290 mg N/L assimilable nitrogen. The overall nitrogen consumed was also estimated in order to determine nitrogen requirement variability. The effect of assimilable nitrogen was in general greater on sugar consumption rates than on growth and 3 kinds of effect on sugar consumption rates were observed: i) existence of an optimal initial nitrogen level for a maximal sugar consumption rate (inhibition if excess), ii) no effect of nitrogen beyond the intermediary level (saturation), iii) sugar consumption rate proportional to the initial nitrogen level (activation). In all cases, the amount of consumed nitrogen increased with its initial concentration and so did the fructophilic capacity of the strains. The optimal requirement varied from 0.62 to 0.91 mg N per g of sugars according to the different strains. There was no general correlation between the sugar assimilation rates and the nitrogen requirement

A model for pH determination during alcoholic fermentation of a grape must by Saccharomyces cerevisiae

A model to predict accurately pH evolution during alcoholic fermentation of must by Saccharomyces cerevisiae is proposed for the first time. The objective at least is to determine if the pH measurement could be used for predictive control. The inputs of the model are: the temperature, the concentrations in sugars, ethanol, nitrogen compounds, mineral elements (magnesium, calcium, potassium and sodium) and main organic acids (malic acid, citric acid, acetic acid, lactic acid, succinic acid). In order to avoid uncertainties coming from the possible precipitation, we studied this opportunity on a grape must without any tartaric acid, known as forming complexes with potassium and calcium during the fermentation. The model is based on thermodynamic equilibrium of electrolytic compounds in solution. The dissociation constants depend on the temperature and the alcoholic degree of the solution. The average activity coefficients are estimated by the Debbye–H¨uckel relation. A fictive diacid is introduced in the model to represent the unmeasured residual species. The molality of hydrogen ions and thus the pH are determined by solving a non-linear algebraic equations system consisted of mass balances, chemical equilibrium equations and electroneutrality principle. Simulation results showed a good capacity of the model to represent the pH evolution during fermentation

Highlight on the problems generated by p-coumaric acid analysis in fermentations

p-Coumaric acid is a natural hydroxycinnamic acid existing in grapes and wine. It is the precursor of the 4-ethylphenol molecule through the bioconversion reaction by Brettanomyces yeast. Chromatographic methods are the most common techniques to detect p-coumaric acid. It is known that this acid is highly unstable in analysis and fermentation experiments. This paper highlights the problems occurring in p-coumaric acid analysis in wine fermentation conditions when studying its bioconversion. First, it was shown that p-coumaric acid was unstable at elevated temperature. On the other hand, it was found that in our experimental conditions p-coumaric acid reacted with ethanol. This work revealed also that the p-coumaric acid is partially adsorbed on Brettanomyces yeast, certainly on cell walls. Because of these phenomena the quantity of p-coumaric acid which can participate to the bioconversion into ethylphenol decreases

Batch fermentation process: Modelling and direct sensitivity analysis

Based on a nonlinear model, this article realizes an investigation of dynamic behaviour of a batch fermentation process using direct sensitivity analysis (DSA). The used nonlinear mathematical model has a good qualitative and quantitative description of the alcoholic fermentation process. This model has been discussed and validated by authors in other studies. The DSA of dynamic model was used to calculate the matrix of the sensitivity functions in order to determine the influence of the small deviations of initial state, control inputs, and parameters from the ideal nominal values on the state trajectory and system output in time. Process optimization and advanced control strategies can be developed based on this work

Fermentative capability and aroma compound production by yeast strains isolated from Agave tequilana Weber juice

Five yeast strains isolated from agave juice were studied for their fermentative and aromatic capacity. The experiments were performed using agave juice supplemented with ammonium sulphate, as is commonly done in tequila distilleries. Three strains classified as Saccharomyces cerevisiae showed high biomass and ethanol production, as well as higher ethanol tolerance than those classified as Kloeckera africana and Kloeckera apiculata, which showed scarce growth. The results suggest that Kloeckera strains were affected by nutritional limitation and/or toxic compounds present in agave juice. Agave juice analyses showed a lower amino acid content than those reported in grape juice. S. cerevisiae strains produced predominantly amyl and isoamyl alcohols, n-propanol, 2-phenyl ethanol, succinic acid, glycerol, methanol, isoamyl acetate, ethyl hexanoate, acetaldehyde and isobutanol, whereas Kloeckera strains showed a high production of acetic acid, 2-phenyl ethyl acetate and ethyl acetate. The methanol concentration was significantly different among the yeasts studied. The diversity between three S. cerevisiae strains were higher for the aromatic profile than for genetic level and kinetic parameter. On the other hand, the diversity of Kloeckera yeasts were lower than Saccharomyces yeasts even when belonging to two different species

Effect of temperature on Brettanomyces bruxellensis: metabolic and kinetic aspects

The effect of temperatures ranging from 15 to 35 °C on a culture of Brettanomyces bruxellensis was investigated in regards to thermodynamics, metabolism, and kinetics. In this temperature range, we observed an increase in growth and production rates. The growth behavior was well represented using the Arrhenius model, and an apparent activation energy of 16.61 kcal/mol was estimated. A stuck fermentation was observed at 35 °C as represented by high cell death. The carbon balance established that temperature had no effect on repartition of the glucose consumption between biomass and products. Hence, the same biomass concentration was obtained for all temperatures, except at 35 °C. Moreover, using logistic and Luedeking–Piret models, we demonstrated that production rates of ethanol and acetic acid were partially growth associated. Parameters associated with growth (αeth and αaa) remained constant with changing temperature, whereas, parameters associated with the population (βeth and βaa) varied. Optimal values were obtained at 32 °C for ethanol and at 25 °C for acetic acid

Influence de l'étape de croissance et de la quantité de brettanomyces bruxellensis sur la production d'éthyl-phenols

Influence de l'étape de croissance et de la quantité de brettanomyces bruxellensis sur la production d'éthyl-phenol

Développement d’un procédé continu de fermentations alcoolique et maloalcoolique simultanées pour la vinification en rouge.

Développement d’un procédé continu de fermentations alcoolique et maloalcoolique simultanées pour la vinification en rouge

The role of malic acid in the metabolism of Schizosaccharomyces pombe: substrate consumption and cell growth

The effect of initial concentrations of malate varying from 0 to 28.6 g/l was studied. The acid was found to be inhibitory for growth of Schizosaccharomyces pombe but not for its deacidification activity. Malate was never integrated into biomass but partly transformed into ethanol if the aeration rate was weak (oxygen limitation). In the absence of glucose, resting cells of S. pombe were able to degrade malic acid if their concentration was sufficient, but their viability gradually decreased. However, for 0.15 g/l of growing cells (inoculum) 6 g/l of glucose was necessary to consume 8 g/l of malate. When the medium did not contain sugar no growth was observed despite the partial consumption of malate, showing that the acid was neither a carbon source nor an energy source