Most significant biotechnological improvements on the production process of wine, beer and bread

Abstract

Saccharomyces cerevisiae is the most used yeast in the alimentary field due to its ability to do different types of fermentation, such as the alcoholic one. Thanks to this metabolic process, we can benefit of many products such as bread, wine and beer, since the prehistory. This work is a bibliographic research about the most significant biotechnological improvements for the optimization of these industrial food processes based on both genetic modifications and domestication of S. cerevisiae. To carry out this final degree work, the scientific database PubMed and printed books from the library of the University of Girona and other internet searches were used. Related to wine, the resistance mechanism of S. cerevisiae against high concentrations of sulphites, which cause cell toxicity, has been studied for years. It has been shown that the most effective ways to facilitate this resistance by domestication strategies are the use of strains capable of forming a non-toxic complex with acetaldehyde or consuming sulphites by the sulphite reductase enzyme, sulphitolysis by glutathione and, overexpression of the SSU1 gene, encoding a sulphite pump that detoxifies the cell. To improve wine quality, genetic engineering is used to give more body and sweetness, for example by glycerol overproduction. Also, for a more fruity taste a strain able to liberate the monoterpenes containing in grape, by breaking the glycosidic bond is required. Finally, to avoid wine acidification, malic acid consumption is improved in the malolactic fermentation.

In beer production, biotechnological improvements have been mainly achieved by genetic engineering, which has focused on the clarification by the degradation of linear polymers of glucose S. cerevisiae, conferring to it the ability to secrete endoglucanases. For the production of low calorie beer, it has been improved the S.cerevisae’s ability to degradate dextrins and other carbohydrates derived from starch. The use of transgenic strains of S.cerevisae, able to to transform the α-acetolactate to acetoin, has overcome the problem of the accumulation of diacetyl at the end of fermentation, product that gives to the beer an undesired sweeteness; acetoin does not affect the taste. Concerning to the production of bread, several strategies have been developed for producing large-scale S.cerevisiae biomass cheaply; for this purpose, the melibiose consumption from molasses has been optimized to use it as a carbon source. It has also been studied the use of strains that prioritize the utilization of maltose and, thus increase the speed of the baking process. Finally, it has been studied how to overcome the effects of thermal stress caused by the freezing of S. cerevisiae strains used in the baking process; the overexpression of genes for cold protection and also of aquaporins that helps to preserve cell viability have been successfully tested