Multifactorial analysis of acetaldehyde kinetics during alcoholic fermentation by Saccharomyces cerevisiae

Acetaldehyde is the terminal electron acceptor in the alcoholic fermentation by Saccharomyces cerevisiae. Quantitatively the most important carbonyl by-product, it has relevance for ethanol production yields as well as product stabilization and toxicology. The aim of this study was to investigate the effect of various enological parameters on acetaldehyde kinetics during alcoholic fermentations. Two commercial yeast strains were tested in two grape musts and the pH, temperature, SO₂ and nutrient addition were varied. All incubations had uniform kinetics where acetaldehyde reached an initial peak value followed by partial reutilization. Peak acetaldehyde concentrations and residual concentrations after 15 days of fermentations ranged from 62 to 119 mg l^− 1 and 22 to 49 mg l^− 1, respectively. A positive linear relationship was found between peak and final acetaldehyde levels in Gewürztraminer, but not Sauvignon Blanc fermentations, where sluggish fermentations were observed. Several factors had a significant effect on peak and/or final acetaldehyde levels. SO₂ addition, grape cultivar and fermentation nutrition were important regulators of peak acetaldehyde production, while final acetaldehyde concentrations were correlated with SO₂ addition, grape cultivar and temperature. The results allowed to estimate the acetaldehyde increase caused by SO₂ addition to 366 ??g of acetaldehyde per mg of SO₂ added to the must. The course of the final fermentation phase was shown to determine acetaldehyde residues. Comparison of acetaldehyde and hexose kinetics revealed a possible relationship between the time of occurrence of peak acetaldehyde concentrations and the divergence of glucose and fructose degradation rates.     

Saccharomyces cerevisiae fermentation product in dairy cow diets containing dried distillers grains plus solubles

Sixteen multiparous Holstein cows (127 ± 52 d in milk) were used in 4 replicated 4 × 4 Latin squares with 4-wk periods to evaluate interactions of dietary inclusion of a fermentation product of Saccharomyces cerevisiae (SC; XPC, Diamond V Mills, Cedar Rapids, IA) and dried distillers grains plus solubles (DDGS) on production of milk and milk components when fed diets containing approximately 30% dietary neutral detergent fiber with calculated forage neutral detergent fiber of 19.3% of diet dry matter (DM). Treatments were a 2 × 2 factorial arrangement with SC included at 0 or 14 g/d and DDGS at 0 or 20% of diet DM. Diets consisted of 27% corn silage, 18% alfalfa hay, and 55% concentrate mix on a DM basis. Diets not containing DDGS included additional corn, soybean meal, expeller soybean meal, soyhulls, and rumen inert fat to remain isocaloric and isonitrogenous with DDGS diets. Dry matter intake (26.0 kg/d) was similar for all diets. Milk production increased with the addition of SC to diets (43.6 vs. 42.0 kg/d for diets without SC) and decreased for cows fed diets containing DDGS (42.0 kg/d vs. 43.6 kg/d for diets not containing DDGS). Milk fat percentage (3.05 vs. 3.22% for DDGS and non-DDGS diets, respectively) and yield (1.27 vs. 1.41 kg/d) were decreased by the addition of DDGS but were not affected by the addition of SC. Concentrations of long-chain, polyunsaturated, trans-, and conjugated fatty acids in milk of cows fed DDGS were increased, but milk fatty acid profiles were not affected by SC. Milk true protein concentrations were similar for all diets; however, the addition of SC increased yield of true protein (1.32 vs. 1.27 kg/d). Concentrations of milk urea nitrogen increased when SC was included in the diet with DDGS. The DDGS decreased yields of energy-corrected milk (39.4 vs. 42.1 kg/d) and tended to decrease feed efficiency (1.53 vs. 1.61 kg of energy-corrected milk/kg of dry matter intake). Body weights and condition scores were not affected by treatments. Results suggest that diets containing minimal amounts of forage fiber and DDGS at 20% of diet DM will contribute to decreased milk production and milk fat depression. The addition of SC did improve milk and milk protein yields but did not prevent milk fat depression caused by DDGS. Production responses to SC were similar when cows were fed DDGS or non-DDGS diets.     

Aromatic series in sherry wines with gluconic acid subjected to different biological aging conditions by Saccharomyces cerevisiae var. capensis

Wines from healthy grapes supplemented with gluconic acid were subjected to biological aging under two experimental conditions. The first one was carried out under flor yeast velum as in the traditional biological aging and the second one under submerged cultures. The highest gluconic acid consumption was observed in aged wines in submerged cultures. Nine aromatic series were obtained by grouping the 48 volatile compounds quantified in wines. The aroma profile based on the aromatic series allows comparison of the changes due to the gluconic acid consumption and the changes due to the different aging conditions assayed. Only the herbaceous and fatty series showed diminished values of consequence of gluconic acid consumption. The fatty, herbaceous and roasty series show highest values, whereas the fruity, floral, solvent and medicinal series reached lower values in the submerged cultures assay. The application of the assay conditions to winemaking can reduce the gluconic acid concentration in wines obtained from rotten grapes.     

Changes in the Lipid Composition of Saccharomyces cerevisiae Race Capensis (G-1) During Alcoholic Fermentation and Flor Film Formation

The cellular lipid composition of one flor-forming strain of Saccharomyces cerevisiae during fermentation and the subsequent period of film formation with different oxygen levels was studied. Irrespective of fermentation conditions, only those yeasts which came into contact with oxygen after fermentation formed a flor film. After the fermentation, these yeasts entered an adaptation phase in which the percentage of oleic acid increased considerably at the expense of other long-chain fatty acids. Their phospholipid contents remained high, as well as the unsaturation index of their fatty acids and the ergosterol/phospholipids ratio was maintained below 1. These changes allowed an increased viability of yeasts in the wine of up to 80% and the acquisition of sufficient hydrophobicity and floatability to reach the surface and form flor film.     

High-cell-density fermentation of Saccharomyces cerevisiae for the optimisation of mead production

Mead is a traditional drink that contains 8%–18% (v/v) of ethanol, resulting from the alcoholic fermentation of diluted honey by yeasts. Mead fermentation is a time-consuming process and the quality of the final product is highly variable. Therefore, the present investigation had two main objectives: first, to determine the adequate inoculum size of two commercial wine-making strains of Saccharomyces cerevisiae for the optimisation of mead fermentation; and second, to determine if an increase in yeast pitching rates in batch fermentations altered the resulting aroma profiles. Minor differences were detected in the growth kinetics between the two strains at the lowest pitching rate. With increasing pitching rates net growth of the strain ICV D47 progressively decreased, whereas for the QA23 the increasing inoculum size had no influence on its net growth. The time required to reach the same stage of fermentation ranged from 24 to 96 h depending on the inoculum size. The final aroma composition was dependent on the yeast strain and inoculum size. Fourteen of the twenty-seven volatile compounds quantified could contribute to mead aroma and flavour because their concentrations rose above their respective thresholds. The formation of these compounds was particularly pronounced at low pitching rates, except in mead fermented by strain ICV D47, at 10⁶ CFUs/mL. The esters isoamyl acetate, ethyl octanoate and ethyl hexanoate were the major powerful odourants found in the meads. The results obtained in this study demonstrate that yeast strain and inoculum size can favourably impact mead's flavour and aroma profiles.     

Oleic acid and ergosterol supplementation mitigates oxidative stress in wine strains of Saccharomyces cerevisiae

During fermentation of high-sugar-containing medium lacking lipid nutrients, wine yeasts undergo oxidative stress and oxidative damage to cell membranes and proteins. Considering that cell membranes are important stress sensors, and that under hypoxic conditions wine yeasts modulate cell membranes composition by incorporating lipids available in the growth medium, in the present work, the effects of lipid nutrition on wine yeast oxidative stress response were evaluated on two strains of Saccharomyces cerevisiae. Biomarkers of oxidative stress, oxidative damage and antioxidant response were evaluated together with viability and acetic acid production during fermentation of a synthetic must lacking lipid nutrients as compared to added oleic acid and ergosterol. The results show that the availability of lipid nutrients causes a significant reduction in the intracellular content of reactive oxygen species and in the oxidative damage to membranes and proteins, as indicated by flow cytometry of cells stained with dihydroethidum (DHE) and propidium iodide (PI) and by Western blot of protein carbonyls. Accordingly, lipid nutrients feeding results in the increase in cell viability and superoxide activity, and the reduction in trehalose accumulation, proteinase A activity and production of acetic acid. In summary, these results are compatible with the hypothesis that the supplementation of lipid nutrients mitigates oxidative stress and oxidative damage in wine strains of S. cerevisiae during growth under unfavourable conditions.     

Redox effect on volatile compound formation in wine during fermentation by Saccharomyces cerevisiae

Although redox state is a well-known key process parameter in microbial activity, its impact on wine volatile aroma compounds produced during fermentation has not been studied in detail. In this study we report the effect of reductive and microaerobic conditions on wine aroma compound production using different initial amounts of yeast assimilable nitrogen (YAN: 180 and 400 mg N/l) in a simil grape must defined medium and two S. cerevisiae strains commonly used in wine-making. In batch fermentation culture conditions, reductive conditions were obtained using flasks plugged with Muller valves filled with sulphuric acid; while microaerobic conditions were attained with defined cotton plugs. It was found that significant differences in redox potential were obtained using the different plugs, and with variation of over 100 mV during the main fermentation period.     

Purification and characterisation of Saccharomyces cerevisiae external invertase isoforms

Four external invertase isoforms (EINV1, EINV2, EINV3 and EINV4) from Saccharomyces cerevisiae were highly purified by isoelectric precipitation, ethanol precipitation, ion-exchange on QAE-Sephadex and gel filtration using Sephacryl S-200. Unlike previously published procedures for external invertase purification, a specially designed step elution was applied on QAE-Sephadex which enabled the separation of four isoforms. The isoforms have the same molecular mass and catalytic properties: K_m for sucrose (25.6 mM), pH optimum (3.5–5.0) and temperature optimum (60 °C), but they exhibit significant difference in pI values, thermal stability and chemical reactivity. Deglycosylation studies showed that the observed differences between isoforms arise from posttranslational modifications. Results showed that external invertase is a mixture of at least four isoforms, but in order to improve the efficiency of food industry processes, only the most stable isoform (EINV1) should be purified and utilised. Substantially different chemical reactivity of the isoforms could be used to improve the yield of covalent immobilization procedures.     

Biogenic amine production by Oenococcus oeni during malolactic fermentation of wines obtained using different strains of Saccharomyces cerevisiae

Twenty-six wild Oenococcus oeni strains were investigated for their ability to form biogenic amines during malolactic fermentation in synthetic medium and in wine. Eight strains produced histamine and tyramine in screening broth at concentrations of 2.6-5.6 mg/L and 1.2-5.3 mg/L, respectively. Based on their ability to form biogenic amines, five strains were selected to inoculate three wines obtained by the fermentation of three different Saccharomyces cerevisiae strains (A, B, and C). All bacterial strains could perform malolactic fermentation for short periods in wine C, whereas only one strain performed complete malolactic fermentation in wines A and B. Two O. oeni strains (261 and 351) produced histamine and tyramine in wine C. Time-course analysis of these compounds showed that for both strains, histamine and tyramine production began at day 10 and finished on day 25, after the end of malolactic fermentation. These results indicate that the ability of O. oeni to produce histamine and tyramine is dependent on the bacterial strain and on the wine composition, which in turn depends on the yeast strain used for fermentation, and on the length of bacteria-yeast contact time after the completion of malolactic fermentation.     

Fruit wine produced from cagaita (Eugenia dysenterica DC) by both free and immobilised yeast cell fermentation

The aims of this work were to elaborate a fruit wine from cagaita (Eugenia dysenterica DC) pulp and to compare the fermentations conducted with free and with Ca-alginate immobilised cells. Two strains of Saccharomyces cerevisiae (UFLA CA11 and CAT-1) were tested and four fermentation batches were performed, in triplicate, at 22 °C for 336 h: UFLA CA11 in free and immobilised cells and CAT-1in free and immobilised cells. Fermentation time and ethanol production were influenced by the yeast strain and by the cell status, with immobilised cells of UFLA CA11 and CAT-1 fermenting faster (4 days and 8 days, respectively) than UFLA CA11 and CAT-1 free cells (10 days and 12 days, respectively). Ethanol content (g/L) was slightly higher when the fermentation was conducted with free cells (94.63 and 94.94 for UFLA CA11 and CAT-1, respectively) than with immobilised cells (86.82 and 87.21 for UFLA CA11 and CAT-1, respectively). The beverage from CAT-1 free cells showed the highest concentration of higher alcohols (82,086.12 ??/L), whereas the lowest concentration (37,812.17 ??/L) was found in the beverage from immobilised UFLA CA11. The ethyl ester concentration ranged from 1511.42 ??/L (CAT-1 free cells) to 2836.34 ??/L (UFLA CA11 free cells). According to the sensory evaluation, the fruit wine acceptability was greater than 70% for colour, flavour and taste for all cagaita beverages.     

Effect of grape indigenous Saccharomyces cerevisiae strains on Montepulciano d'Abruzzo red wine quality

The growth of selected, indigenous Saccharomyces cerevisiae added as starters (SRS1, MS72 and RT73) was monitored during Montepulciano d'Abruzzo wine production. In all the fermentations the addition of the starter, caused a decrease of the non-Saccharomyces yeasts. When strains MS72 and RT73 were used as starters they were detected in the first phases of fermentations, while strain SRS1 competed successfully with native yeasts during all the process. Wines obtained by fermentation with the indigenous starters showed some different characteristics, according to the chemical and sensory analyses. This study highlighted that among selected starters with high fermentative capacity, some are able to dominate better than other natural wine yeast biota, whereas some strains can interact and survive besides native yeast populations during the fermentation. As a consequence, the dominance character can have a positive or negative effect on wine quality and has to be considered in the frame of yeast selection in order to improve or characterize traditional wines. Winemakers could choose among different degrees of yeast dominance to modulate the interaction among starter and native wine yeast population.     

Fractionation of glycoside aroma precursors in neutral grapes. Hydrolysis and conversion by Saccharomyces cerevisiae

Glycoconjugated aroma precursors from neutral grape varieties were fractionated on 5 g C18 RP cartridge. Each of the seven fractions collected was divided in three parts: first part was hydrolysed with Pectinol in order to determine total aromatic heterosides, while the second part was treated with an active strain of the yeast Saccharomyces cerevisiae UCLM 325 and the third part with acetonic powder of the same yeast strain. The studied strain proved effective in the hydrolysis of the heterosides of nerol and geraniol, cis-8-hydroxy-linalool, 8-hydroxy-dihydro-linalool, some benzenoids and some norisoprenoids derivatives such as vomifoliol and 3-oxo-α-ionol. Only whole cells are able to convert geraniol to citronellol.     

Meta-analysis of the influence of Saccharomyces cerevisiae supplementation on ruminal parameters and milk production of ruminants

The effects of yeast supplementation on intake, production, and rumen fermentation characteristics have been widely studied, but results are inconsistent between different studies. A quantitative meta-analysis was applied to 110 papers, 157 experiments, and 376 treatments dealing with yeast supplementation in ruminants. The objective was first to highlight the major quantitative effects of live yeast supplementation on intake, rumen fermentation, and milk production, and second, to identify major differences in experimental conditions between studies that can affect the response to treatment. Some of these experimental conditions are referred to as interfering factors. Yeast supplementation increased rumen pH (+0.03 on average) and rumen volatile fatty acid concentration (+2.17 mM on average), tended to decrease rumen lactic acid concentration (−0.9 mM on average), and had no influence on acetate-to-propionate ratio. Total-tract organic matter digestibility was also increased by yeast supplementation (+0.8% on average). Yeast supplementation increased dry matter intake (DMI; +0.44 g/kg of body weight; BW), milk yield (+1.2 g/kg of BW), and tended to increase milk fat content (+0.05%), but had no influence on milk protein content. Dose effects of yeast supplementation, expressed as log₁₀ [1+(cfu per 100 kg of BW)], globally confirmed the qualitative effects observed in the first analysis. The positive effect of yeast supplementation on rumen pH increased with the percentage of concentrate in the diet and with the DMI level. It was negatively correlated with the level of dietary neutral detergent fiber (NDF). The positive effect of yeast supplementation on rumen volatile fatty acid concentration increased with DMI and crude protein levels. The positive effect of yeast supplementation on organic matter digestibility increased with the percentage of concentrate and NDF in the diet. The negative effect of yeast supplementation on lactic acid concentration tended to decrease when the DMI level and the percentage of concentrate in the diet increased. The effects of interfering factors were globally similar when either dose effect or qualitative effect of yeast was taken into account. Although rumen fermentation efficiency per se was not measured, these results suggest an improvement in rumen fermentation by yeast supplementation. This effect could, however, be modulated by several different factors such as DMI, percentage of concentrate or NDF in the diet, or species.