Saccharomyces alcohol fermentation

Alcoholic Fermentation. Certain types of starchy biomass such as com and high sugar crops are readily converted to ethanol under anaerobic fermentation conditions ia the presence of specific yeasts Saccharomyces cerevisia and other organisms (Fig. 6). However, alcohoHc fermentation of other types of biomass, such as wood and municipal wastes that contain high concentrations of cellulose, can be performed ia high yield only after the ceUulosics are converted to sugar concentrates by acid- or enzyme-catalyzed hydrolysis ... 

The catalytic capacity of several excreting pectolytic enzymes obtained from various yeast strains was examined using in vivo and biochemical techniques. Of the 33 yeast strains studied 30 were isolated from champagne wine during alcoholic fermentation. Only one yeast strain was found to excrete pectolytic enzymes and was identified as Saccharomyces cerevisiae designated SCPP. Three types of pectolytic enzymes were found to be excreted by SCPP polygalacturonase (PG), pectin-lyase (PL) and pectin-esterase (PE) [1]. 

A. Picard, I. Daniel, G. Montagnac and P. Oger, In situ monitoring by quantitative Raman spectroscopy of alcoholic fermentation by Saccharomyces cerevisiae under high pressure, Extremophiles, 11, 445 52 (2007). 

Fig. 10.1 Precursors, intermediates, and metabolites of the main groups of flavour compounds produced during alcoholic fermentation of carbohydrates by Saccharomyces cerevisiae yeast... 

In addition to malo-lactic fermentation, another biological method for deacidification of high-acid must is to use malic acid-metabolizing Schizo-saccharomyces yeast for the alcoholic fermentation. Benda and Schmidt (33) have selected strains of these yeasts which produce wines with no off-flavors. In using some of these same strains we have also been able to make wines of sound character (18). 

A set of alcoholic fermentations experiments was conducted in order to verify the performance of the model-based substrate sensor. Diluted molasses was used in the experiments as feed substrate and bread yeast, Saccharomyces cerevisiae, as inoculum. The operational conditions and kinetic parameters used are given in Table 1 for two different experiments (tests 1 and 2), and values of ethanol and biomass concentrations were also determined off-line using gas chromatography (CG) and dry cell weight standard (7) methods, respectively. 

Sherry wines are obtained from young wines, carefully selected soon after completing fermentation. These are typically fortified by adding vinous alcohol until they reach an alcohol content of 15-15.5°. They are subsequently transferred to oak barrels before being aged. In most sherries, wine aging occurs in the so-called solera and criaderas system under the flor film of yeast. Once alcoholic fermentation is finished, races of Saccharomyces cerevisiae that can grow on the surface of the wine switch from fermentative to oxidative (respiratory) metabolism. They spontaneously form a biofilm called flor on the wine surface. 

Mauricio, J. C., Ortega, J. M., and Salmon, J. M. (1995). Sugar uptake by three strains of Saccharomyces cerevisiae during alcoholic fermentation at different initial ammoniacal nitrogen concentrations. Acta Horticult. 388,197-202. 

Mendes-Ferreira, A., Cosme, F., Barbosa, C., Falco, V., Ines, A., and Mendes-Faia, A. (2010). Optimization of honey-must preparation ad alcoholic fermentation by Saccharomyces cerevisiae for mead production. Int. J. Food Microbiol. 144,193-198. 

In the meanwhile, yeasts adapt themselves to the cold conditions and begin alcoholic fermentation. Fermentation is slow but regular, usually carried out by Saccharomyces cereuisiae and Saccharomyces bayanus. The fermentation has to be kept under constant surveillance as the low temperatures, combined with the high sugar content, may lead to premature and unwanted fermentation cessation, even when selected cultures of yeasts are added. 

On the other hand, the inoculation of selected dry yeasts greatly increases the initial population of Saccharomyces cerevisiae. Nowadays, most wineries inoculate selected dry yeast in order to guarantee alcoholic fermentation without any deviation. However, other wineries, especially traditional wine cellars, continue to use spontaneous alcoholic fermentation because they believe it gives their wines greater complexity. 

As was quoted above, when fermenting grape juice, Saccharomyces cerevisiae mainly directs the pyruvate to produce of ethanol in order to regenerate the NAD+ consumed by glycolysis. This process, called alcoholic fermentation, is shown in Fig. 1.4. 

Moreover, during alcoholic fermentation very important changes take place in the yeast s environment. Basically, the ethanol concentration increases progressively and yeasts need to adapt their plasmatic membranes to this aggressive new environment (Weber and Bont 1996). Apparently, the presence of ethanol in the medium alters drastically the fluidity of the membrane (Jones and Greenfield 1987). Under these conditions, Saccharomyces cerevisiae must increase its proportion of sterols and unsaturated fatty acids to compensate for this effect and consequently... 

Salmon, J.M., Vezinhet, E, Barre, P. (1987) Anabolic role of L-malic acid in Saccharomyces cerevisiae in anaerobiosis during alcoholic fermentation. FEMS Microbiol. Lett., 42, 213-220. 

The biological aging of wines has aroused increasing interest in recent years, as reflected in the large number of papers on this topic over the last decade. Biological aging in wine is carried out by flor yeasts. Once alcoholic fermentation has finished, some Saccharomyces cerevisiae yeast races present in wine switch from a fermentative metabolism to an oxidative (respiratory metabolism) and spontaneously form a biofllm called flor on the wine surface. Wine under flor is subject to special conditions by effect of oxidative metabolism by yeasts and of the reductive medium established as they consume oxygen present in the wine. These conditions facilitate... 

Valero, E., Millan, C., Ortega, J.M. (2002). Changes in the lipid composition of Saccharomyces cerevisiae race capensis (Gl) during alcoholic fermentation and flor film formation. Lebensm. Wiss. Technol, 35, 593-599. 

Rlata, C., Mauricio, J.C., Millan, C., Ortega, J. M. (2005) Influence of glucose and oxygen on the production of ethyl acetate and isoamyl acetate by a Saccharomyces cerevisiae strain during alcoholic fermentation. World Journal of Microbiology Biotechnology, 21, 115-121. 

Redzepovic, S., Orlic, S., Majdak, A., Kozina, B., Volschenk, H., Viljoen-Bloom, M. (2003) Differential malic acid degradation by selected strains of Saccharomyces during alcoholic fermentation. International Journal of Food Microbiology, 83, 49-61. 

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