Roberto Pérez-Torrado

The increasing demand for beers with moderate ethanol content and diversified sensory profiles has stimulated the search for non-GMO yeast-based strategies that preserve brewing performance. In this study, a collection of 28 yeast strains from different species and isolation sources was screened to identify parental strains with complementary fermentative and metabolic traits. Based on their performance under brewing conditions, selected parents were crossed by rare-mating to generate a novel interspecific hybrid, DR1 ( Saccharomyces cerevisiae × Saccharomyces paradoxus ), which was molecularly confirmed and subsequently characterized. The fermentative behavior of DR1 was assessed in comparison with its parental strains under representative and industrial brewing conditions. DR1 retained efficient maltose consumption but showed limited maltotriose utilization, resulting in a moderate ethanol reduction relative to the industrial parent, reaching 21 % in synthetic wort and 17.5 % in industrial wort. The hybrid also produced higher glycerol and a volatile profile enriched in selected acetate and fatty acid esters. Consumer sensory analysis showed that DR1 retained beer-like sensory attributes, although overall liking and purchase intention were lower than for the industrial parent, indicating that further optimization will be required for broad consumer acceptance. Overall, this work supports rare-mating-based interspecific hybridization as a non-GMO strategy to generate brewing yeasts with reduced ethanol production and expanded aromatic diversity.

The use of unconventional yeast species in human‐driven fermentations has attracted a lot of attention in the last few years. This tool allows the alcoholic beverage industries to solve problems related to climate change or the consumer demand for newer high‐quality products. In this sense, one of the most attractive species is Saccharomyces kudriavzevii, which shows interesting fermentative traits such as the increased and diverse aroma compound production in wines. Specifically, it has been observed that different isolates of this species can produce higher amounts of higher alcohols such as phenylethanol compared with Saccharomyces cerevisiae . In this work, we have shed light on this feature relating it to the S. kudriavzevii aromatic amino acid anabolic pathway in which the enzyme Aro4p plays an essential role. Unexpectedly, we observed that the presence of the S. kudriavzevii ARO4 variant reduces phenylethanol production compared with the S. cerevisiae ARO4 allele. Our experiments suggest that this can be explained by increased feedback inhibition, which might be a consequence of the changes detected in the Aro4p amino end such as L ₂₆ Q ₂₄ that have been under positive selection in the S. kudriavzevii specie.

Food consumption of healthier products has become an essential trend in the food sector. This is also the case in beer, a biochemical process of transformation performed by yeast cells. More and more studies proclaim the need to reduce ethanol content in alcoholic drinks, certainly the most important health issue of beer consumption. In this review we gather key health issues related to beer consumption and the last advances regarding the use of yeast to attenuate those health problems. Furthermore, we have included the latest findings about the general positive impact of yeast in health as a consequence of its ability to biotransform polyphenolic compounds present in the wort, producing healthy compounds as hydroxytyrosol or melatonin, and its ability to perform as a probiotic driver. Besides, a group of population with chronic diseases as diabetes or celiac disease could take advantage of low carbohydrate or gluten-free beers, respectively. The role of yeast in beer production has been traditionally associated to its fermentative power. But here we have found a change in this dogma in the last years toward yeasts being a main driver to enhance healthy aspects of beer. The key findings are discussed and possible future directions are proposed.

Summary: Phenylethanol (PE) and phenylethyl acetate (PEA) are commonly desired compounds in wine because of their rose‐like aroma. The yeast S. cerevisiae produces the PE either through de novo biosynthesis by shikimate pathway followed by the Ehrlich pathway or the direct phenylalanine catabolism via Ehrlich pathway, and then converted into PEA. Previous work demonstrated that, compared to S. cerevisiae , other Saccharomyces species, such as S. kudriavzevii and S. uvarum , produce higher concentrations of PE and PEA from the precursor phenylalanine, which indicates differential activities of the biosynthetic‐involved enzymes. A previous in‐silico analysis suggested that the transcriptional activator Aro80p is one of the best candidates to explain these differences. An improved functional analysis identified significant radical amino acid changes in the S. uvarum and S. kudriavzevii Aro80p that could impact the expression of the catabolic genes ARO9 and ARO10 , and hence, the production of PE from phenylalanine. Indeed, wine S. cerevisiae strains carrying the S. uvarum and S. kudriavzevii ARO80 alleles increased the production of both compounds in the presence of phenylalanine by increasing the expression of ARO9 and ARO10 . This study provides novel insights of the unidentified Aro80p regulatory region and the potential usage of alternatives ARO80 alleles to enhance the PE and PEA concentration in wine.

In the study of the unfolded protein response pathway, it is essential to determine the amount of unfolded proteins that the cell is accumulating. Besides being essential it is one of the most challenging technique because of the difficulty to detect unfolded proteins without producing protein denaturation with the method itself. Thus, indirect methods became very useful as the use of fluorescent proteins. In this chapter, we present some of the most used methods to indirectly measure protein folding in living cells using fluorescent proteins.

Different species can find convergent solutions to adapt their genome to the same evolutionary constraints, although functional convergence promoted by chromosomal rearrangements in different species has not previously been found. In this work, we discovered that two domesticated yeast species, Saccharomyces cerevisiae, and Saccharomyces uvarum, acquired chromosomal rearrangements to convergently adapt to the presence of sulfite in fermentation environments. We found two new heterologous chromosomal translocations in fermentative strains of S. uvarum at the SSU1 locus, involved in sulfite resistance, an antimicrobial additive widely used in food production. These are convergent events that share similarities with other SSU1 locus chromosomal translocations previously described in domesticated S. cerevisiae strains. In S. uvarum, the newly described VII^XVI and XI^XVI chromosomal translocations generate an overexpression of the SSU1 gene and confer increased sulfite resistance. This study highlights the relevance of chromosomal rearrangements to promote the adaptation of yeast to anthropic environments.

Editorial: New Advances in Genetic Studies to Understand Yeast Adaptation to Extreme and Fermentative Environments