Influence of Nutrient Supplementation on Torulaspora Delbrueckii Wine Fermentation Aroma

Engineering a fermenting yeast able to produce the fragrant β-ionone apocarotenoid for enhanced aroma properties in wine

Wine is composed of multitudinous flavour components and volatile organic compounds that provide this beverage with its attractive properties of taste and aroma. The perceived quality of a wine can be attributed to the absolute and relative concentrations of favourable aroma compounds; hence, increasing the detectable levels of an attractive aroma, such as β-ionone with its violet and berry notes, can improve the organoleptic qualities of given wine styles. We here describe the generation of a new grape-must fermenting strain of Saccharomyces cerevisiae that is capable of releasing β-ionone through the heterologous expression of both the enzyme carotenoid cleavage dioxygenase 1 (CCD1) and its substrate, β-carotene. Haploid laboratory strains of S. cerevisiae were constructed with and without integrated carotenogenic genes and transformed with a plasmid containing the genes of CCD1. These strains were then mated with a sporulated diploid wine industry yeast, VIN13, and four resultant crosses-designated MQ01-MQ04-which were capable of fermenting the must to dryness were compared for their ability to release β-ionone. Analyses of their fermentation products showed that the MQ01 strain produced a high level of β-ionone and offers a fermenting hybrid yeast with the potential to enhance the organoleptic qualities of wine.

The Use of Hanseniaspora occidentalis in a Sequential Must Inoculation to Reduce the Malic Acid Content of Wine

In this study, the impact of the apiculate yeast Hanseniaspora occidentalis as a co-partner with Saccharomyces cerevisiae was investigated in a sequential-type mixed-culture fermentation of Muscaris grape must. As with other fermentation trials using Hanseniaspora strains, a significant increase in ethyl acetate was observed, but most intriguing was the almost complete abolition of malic acid (from 2.0 g/L to 0.1 g/L) in the wine. Compared to the pure S. cerevisiae inoculum, there was also a marked increase in the concentrations of the other acetate esters. Modulation of some of the varietal elements, such as rose oxide, was also observed. This work shows the promising use of H. occidentalis in a mixed-culture must fermentation, especially in the acid modulation of fruit juice matrices.

Analysis of fungal dynamic changes in the natural fermentation broth of 'Hongyang' kiwifruit

'Hongyang' kiwifruit (Actinidia chinensis Planch.) is an ideal kiwifruit wine variety. At present, there is no research on the dynamic changes of yeast during the natural fermentation of kiwifruit wine. In this study, a high-throughput was employed to analyze the fungal population composition and diversity in the samples cultured in yeast extract peptone dextrose (YPD) medium and enriched in the natural fermentation process of 'Hongyang' kiwifruit at four time points, day one (D1T), day three (D3T), day five (D5T), and day fifteen (D15T). Five hundred and eighty-two operational taxonomic units (OTUs) were obtained from 131 genera and 178 species samples. The diversity analysis results showed that in the early natural fermentation stage, the dominant species was Aureobasidium pullulans, and as natural fermentation proceeded, the genus Pichia became the dominant species. Pichia kluyveri was an important species at the later stages of natural fermentation. An analysis of the metabolic pathways shows that P. kluyveri plays an aromatic-producing role in the natural fermentation of 'Hongyang' kiwifruit. These results could provide a theoretical basis for the studies of kiwifruit fungal diversity and fungal changes during fermentation. The findings could fix a major deficiency in the production of kiwifruit fruit wine, which lacks a specific flavor-producing yeast species or strain.

Biotechnological Importance of Torulaspora delbrueckii: From the Obscurity to the Spotlight

Torulaspora delbrueckii has attracted interest in recent years, especially due to its biotechnological potential, arising from its flavor- and aroma-enhancing properties when used in wine, beer or bread dough fermentation, as well as from its remarkable resistance to osmotic and freezing stresses. In the present review, genomic, biochemical, and phenotypic features of T. delbrueckii are described, comparing them with other species, particularly with the biotechnologically well-established yeast, Saccharomyces cerevisiae. We conclude about the aspects that make this yeast a promising biotechnological model to be exploited in a wide range of industries, particularly in wine and bakery. A phylogenetic analysis was also performed, using the core proteome of T. delbrueckii, to compare the number of homologous proteins relative to the most closely related species, understanding the phylogenetic placement of this species with robust support. Lastly, the genetic tools available for T. delbrueckii improvement are discussed, focusing on adaptive laboratorial evolution and its potential.

Commercially Available Non-Saccharomyces Yeasts for Winemaking: Current Market, Advantages over Saccharomyces, Biocompatibility, and Safety

About 42 commercial products based on non-Saccharomyces yeasts are estimated as available on the market, being mostly pure cultures (79%), with a predominance of Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowia pulcherrima. The others are multi-starter consortia that include non-Saccharomyces/Saccharomyces mixtures or only non-Saccharomyces species. Several commercial yeasts have shown adequate biocompatibility with S. cerevisiae in mixed fermentations, allowing an increased contribution of metabolites of oenological interest, such as glycerol, esters, higher alcohols, acids, thiols, and terpenes, among others, in addition to a lower production of acetic acid, volatile phenols, biogenic amines, or urea. Multi-starter inoculations are also reviewed here, which show adequate biocompatibility and synergy between species. In certain cases, the aromatic profile of wines based on grape varieties considered neutral is improved. In addition, several yeasts show the capacity as biocontrollers against contaminating microorganisms. The studies conducted to date demonstrate the potential of these yeasts to improve the properties of wine as an alternative and complement to the traditional S. cerevisiae.

The potential of spent coffee grounds hydrolysates fermented with Torulaspora delbrueckii and Pichia kluyveri for developing an alcoholic beverage: The yeasts growth and chemical compounds modulation by yeast extracts

This study evaluated the effects of yeast extracts (YE) addition (0 % and 0.25 %, w/v) on the no-volatile and volatile compounds of spent coffee grounds (SCG) hydrolysates fermented with single-cultures of two non-Saccharomyces wine yeasts, Torulaspora delbrueckii and Pichia kluyveri. The added YE improved the growth of both T. delbrueckii and P. kluyveri, especially P. kluyveri, resulting in higher ethanol production (1.98 % vs 1.47 %, v/v) by the latter yeast. In addition, the added YE did not impact on most of the alkaloids production regardless of yeast type, while significantly decreasing the contents of chlorogenic, and caffeic acids in SCG hydrolysates fermented with P. kluyveri. Furthermore, more odor-active compounds such as acetate esters and 2-phenylethyl alcohol were produced when YE was added, and P. kluyveri generated significantly higher amounts of esters compared to that of T. delbrueckii. Moreover, YE addition showed a more noticeable effect on the fermentation performance of P. kluyveri relative to that of T. delbrueckii. These findings indicated the potential of SCG hydrolysates fermented with evaluated non-Saccharomyces yeasts and may expand the applications on utilizing SCG to develop new value-added alcoholic products.

Development of Genetic Modification Tools for Hanseniasporauvarum

Apiculate yeasts belonging to the genus Hanseniaspora are commonly isolated from viticultural settings and often dominate the initial stages of grape must fermentations. Although considered spoilage yeasts, they are now increasingly becoming the focus of research, with several whole-genome sequencing studies published in recent years. However, tools for their molecular genetic manipulation are still lacking. Here, we report the development of a tool for the genetic modification of Hanseniaspora uvarum. This was employed for the disruption of the HuATF1 gene, which encodes a putative alcohol acetyltransferase involved in acetate ester formation. We generated a synthetic marker gene consisting of the HuTEF1 promoter controlling a hygromycin resistance open reading frame (ORF). This new marker gene was used in disruption cassettes containing long-flanking (1000 bp) homology regions to the target locus. By increasing the antibiotic concentration, transformants were obtained in which both alleles of the putative HuATF1 gene were deleted in a diploid H. uvarum strain. Phenotypic characterisation including fermentation in Müller-Thurgau must showed that the null mutant produced significantly less acetate ester, particularly ethyl acetate. This study marks the first steps in the development of gene modification tools and paves the road for functional gene analyses of this yeast.

The Impact of Chitosan on the Chemical Composition of Wines Fermented with Schizosaccharomyces pombe and Saccharomyces cerevisiae

This study investigates the influence of the antimicrobial agent chitosan on a selected Schizosaccharomyces pombe strain during the alcoholic fermentation of ultra-pasteurized grape juice with a high concentration of malic acid. It also studies a selected Saccharomyces cerevisiae strain as a control. The study examines several parameters relating to wine quality, including volatile and non-volatile compounds. The principal aim of the study is to test the influence of chitosan on the final chemical composition of the wine during alcoholic fermentation, and to compare the two studied fermentative yeasts between them. The results show that chitosan influences the final concentration of acetic acid, ethanol, glycerol, acetaldehyde, pyruvic acid, α-ketoglutarate, higher alcohols, acetate esters, ethyl esters, and fatty acids, depending on the yeast species.

The Effect of Non-Saccharomyces and Saccharomyces Non-Cerevisiae Yeasts on Ethanol and Glycerol Levels in Wine

Non-Saccharomyces and Saccharomyces non-cerevisiae studies have increased in recent years due to an interest in uninoculated fermentations, consumer preferences, wine technology, and the effect of climate change on the chemical composition of grapes, juice, and wine. The use of these yeasts to reduce alcohol levels in wines has garnered the attention of researchers and winemakers alike. This review critically analyses recent studies concerning the impact of non-Saccharomyces and Saccharomyces non-cerevisiae on two important parameters in wine: ethanol and glycerol. The influence they have in sequential, co-fermentations, and solo fermentations on ethanol and glycerol content is examined. This review highlights the need for further studies concerning inoculum rates, aeration techniques (amount and flow rate), and the length of time before Saccharomyces cerevisiae sequential inoculation occurs. Challenges include the application of such sequential inoculations in commercial wineries during harvest time.