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Many scholars have explored Saccharomyces cerevisiae alcoholic fermentation (AF) for many millennia in different food processes that are critical to humans. The core purpose of this scientific study was to compare different yeast strain behaviors in brewing, baking, and winemaking processes. Furthermore, researchers intended to investigate the impact of human selection on strains’ food processing in addition to studying both the genetic variability and plasticity of different fermentation products between strains and food processes. The study purposed to analyze the association between metabolic traits, AF kinetics parameters, and traits’ life history during the process of AF. Finally, the study aimed at proposing a new strain selection rationale.
Researchers selected varied strains of S. cerevisiae from different geographical origins and industries of food processing to make a representation of the major strain clusters. They used three synthetic media, which differed in anaerobic growth factor, osmotic pressure, pH, and sugar and nitrogen levels in order to reflect significant changes of fermentation medium between baking, winemaking, and brewing processes. Before inoculation, they further filtered the media through a 0.45-µm nitrate-cellulose membrane. The released carbon dioxide (CO2) amount was determined through automatic measurement of glass reactor weight loss in intervals of 20 minutes. Moreover, researchers regularly monitored cell size and population growth with the use of a particle counter. CO2-specific flux was calculated by dividing the production rate of the gas by the cell number for a particular volume. At the end of AF process, researchers made many dosages. Ethanol concentration determination was done using infrared reflectance while colorimetry was used to measure acetic acid and residual glucose production in continuous flux.
The study results pointed out that human selection focused on completing fermentation for both trehalose and wine content using the S. cerevisiae strains. It was also found that the effect of food processing origin of the studied strains was lower than the medium and strain effects. Such a thing showed weak human selection for the processing of foods. The primary effect of the geographical origin of the strains manifested in the achievement of fermentation. Distillery and beer strains displayed either incomplete or slow fermentation while the wine strains produced more CO2 gas in less time, particularly in the enology medium. It is in the enology medium that the strains consumed all the sugars.
Moreover, the geographical origin had no substantial effect on AF, which indicates that improvement programs of particular food processing industry can exploit the variability of strains utilized in many other industries. The used glucose was analyzed. The analysis revealed plastic and genetic variations in products of fermentation, which indicates that the use of artificial selection is effective in modifying the production of acetate and glycerol among many others. According to this study, the main result showed that the overall maximum CO2 gas production rate was unrelated to the maximum gas production rate for every cell. Contrarily, a highly significant correlation between the maximum size of the population and the overall maximum CO2 production rate was evident in all three media. This finding revealed that human selection did not target metabolic efficiency. Instead, it targeted cellular reproduction efficiency.
All strains are of unique interest because they favor population size, a trait that is related to the rate of fermentation. Human selection targets the ability to complete fermentation. Also, improvement programs have the potential to exploit the variability of strains utilized in many other industries. There is also a genetic and plastic variation in products of fermentation. The selection also aims at targeting cellular production efficiency instead of metabolic efficiency.