Yeast Biotechnology 3.0

A special issue of Fermentation (ISSN 2311-5637). This special issue belongs to the section "Microbial Metabolism, Physiology & Genetics".

Deadline for manuscript submissions: closed (30 November 2019) | Viewed by 79726

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Special Issue Editor

Structural Biology Brussels Lab, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
Interests: yeast biotechnology; cell immobilization; beer brewing biochemistry and fermentation; mini- and microbioreactors; Saccharomyces cerevisiae; Candida; yeast space biology (bioreactors for microgravity research); yeast adhesins; yeast systems biology; glycobiology; nanobiotechnology; atomic force microscopy; protein crystallization; yeast protein structural biology
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Special Issue Information

Dear Colleagues,

Yeasts are truly fascinating microorganisms. Due to their diverse and dynamic activities, they have been used for the production of many interesting products, such as beer, wine, bread, biofuels and biopharmaceuticals. Saccharomyces cerevisiae (bakers’ yeast) is the yeast species that is surely the most exploited by man. Saccharomyces is a top choice organism for industrial applications, although its use for producing beer dates back to at least the 6th millennium BC. Bakers’ yeast has been a cornerstone of modern biotechnology, enabling the development of efficient production processes for antibiotics, biopharmaceuticals, technical enzymes, and ethanol and biofuels. Today, diverse yeast species are explored for industrial applications, such as e.g. Saccharomyces species, Pichia pastoris and other Pichia species, Kluyveromyces marxianus, Hansenula polymorpha, Yarrowia lipolytica, Candida species, Phaffia rhodozyma, wild yeasts for beer brewing, etc.

This Special Issue is focused on recent developments of yeast biotechnology with topics including recent techniques for characterizing yeast and their physiology (including omics and nanobiotechnology techniques), methods to adapt industrial strains (including metabolic, synthetic and evolutionary engineering) and the use of yeasts as microbial cell factories to produce biopharmaceuticals, enzymes, alcohols, organic acids, flavours and fine chemicals, and advances in yeast fermentation technology and industrial fermentation processes.

Topics including but not limited to:

Yeast characterization and analysis
Brewing yeasts (including wild yeasts), wine yeasts, baker’s yeasts.
Evolution and variation of genomes of industrial yeasts.
Yeast systems biology: genomics, proteomics, fluxomics, metabolomics, omics integration.
Yeast nanobiotechnology (nanoanalysis techniques, construction of nanostructures, etc.).

Yeast strain engineering
Yeast metabolic engineering: production of biofuels, secondary metabolites, commodity chemicals, proteins, biopharmaceuticals, material precursors.
Yeast synthetic biology: yeasts as cell factories, tools for controlling enzyme expression levels, strategies for regulating spatial localization of enzymes in yeast, regulatory networks, biomolecular logic gates.
Strain improvement via evolutionary engineering.

Fermentation technology
Industrial bioreactors.
Mini- and microbioreactors: single-cell analysis, high-throughput screening, microfluidic bioreactors.
Process intensification: high-density fermentations, high-gravity fermentation.
Fermentative stress adaptation.

Industrial fermentation processes
Production of food (bread, etc.) and beverages (beer, wine, cider, etc.).
Production of baker’s yeast.
Production of biofuels (bioethanol, 1-butanol, biodiesel, jetfuels), commodity chemicals, pharmaceuticals, material precursors, secondary metabolites.

Prof. Dr. Ronnie G. Willaert
Guest Editor

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Published Papers (16 papers)

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Editorial

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4 pages, 186 KiB  
Editorial
Yeast Biotechnology 3.0
Fermentation 2020, 6(3), 75; https://doi.org/10.3390/fermentation6030075 - 29 Jul 2020
Viewed by 2287
Abstract
This Special Issue is a continuation of the first and second “Yeast Biotechnology” Special Issue series of the journal Fermentation (MDPI) [...] Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)

Research

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17 pages, 1976 KiB  
Communication
PTR-ToF-MS for the Online Monitoring of Alcoholic Fermentation in Wine: Assessment of VOCs Variability Associated with Different Combinations of Saccharomyces/Non-Saccharomyces as a Case-Study
Fermentation 2020, 6(2), 55; https://doi.org/10.3390/fermentation6020055 - 26 May 2020
Cited by 37 | Viewed by 4023
Abstract
The management of the alcoholic fermentation (AF) in wine is crucial to shaping product quality. Numerous variables (e.g., grape varieties, yeast species/strains, technological parameters) can affect the performances of this fermentative bioprocess. The fact that these variables are often interdependent, with a high [...] Read more.
The management of the alcoholic fermentation (AF) in wine is crucial to shaping product quality. Numerous variables (e.g., grape varieties, yeast species/strains, technological parameters) can affect the performances of this fermentative bioprocess. The fact that these variables are often interdependent, with a high degree of interaction, leads to a huge ‘oenological space’ associated with AF that scientists and professionals have explored to obtain the desired quality standards in wine and to promote innovation. This challenge explains the high interest in approaches tested to monitor this bioprocess including those using volatile organic compounds (VOCs) as target molecules. Among direct injection mass spectrometry approaches, no study has proposed an untargeted online investigation of the diversity of volatiles associated with the wine headspace. This communication proposed the first application of proton-transfer reaction-mass spectrometry coupled to a time-of-flight mass analyzer (PTR-ToF-MS) to follow the progress of AF and evaluate the impact of the different variables of wine quality. As a case study, the assessment of VOC variability associated with different combinations of Saccharomyces/non-Saccharomyces was selected. The different combinations of microbial resources in wine are among the main factors susceptible to influencing the content of VOCs associated with the wine headspaces. In particular, this investigation explored the effect of multiple combinations of two Saccharomyces strains and two non-Saccharomyces strains (belonging to the species Metschnikowia pulcherrima and Torulaspora delbrueckii) on the content of VOCs in wine, inoculated both in commercial grape juice and fresh grape must. The results demonstrated the possible exploitation of non-invasive PTR-ToF-MS monitoring to explore, using VOCs as biomarkers, (i) the huge number of variables influencing AF in wine, and (ii) applications of single/mixed starter cultures in wine. Reported preliminary findings underlined the presence of different behaviors on grape juice and on must, respectively, and confirmed differences among the single yeast strains ‘volatomes’. It was one of the first studies to include the simultaneous inoculation on two non-Saccharomyces species together with a S. cerevisiae strain in terms of VOC contribution. Among the other outcomes, evidence suggests that the addition of M. pulcherrima to the coupled S. cerevisiae/T. delbrueckii can modify the global release of volatiles as a function of the characteristics of the fermented matrix. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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9 pages, 1525 KiB  
Article
Yeast Nanometric Scale Oscillations Highlights Fibronectin Induced Changes in C. albicans
Fermentation 2020, 6(1), 28; https://doi.org/10.3390/fermentation6010028 - 21 Feb 2020
Cited by 12 | Viewed by 3891
Abstract
Yeast resistance to antifungal drugs is a major public health issue. Fungal adhesion onto the host mucosal surface is still a partially unknown phenomenon that is modulated by several actors among which fibronectin plays an important role. Targeting the yeast adhesion onto the [...] Read more.
Yeast resistance to antifungal drugs is a major public health issue. Fungal adhesion onto the host mucosal surface is still a partially unknown phenomenon that is modulated by several actors among which fibronectin plays an important role. Targeting the yeast adhesion onto the mucosal surface could lead to potentially highly efficient treatments. In this work, we explored the effect of fibronectin on the nanomotion pattern of different Candida albicans strains by atomic force microscopy (AFM)-based nanomotion detection and correlated the cellular oscillations to the yeast adhesion onto epithelial cells. Preliminary results demonstrate that strongly adhering strains reduce their nanomotion activity upon fibronectin exposure whereas low adhering Candida remain unaffected. These results open novel avenues to explore cellular reactions upon exposure to stimulating agents and possibly to monitor in a rapid and simple manner adhesive properties of C. albicans. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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15 pages, 2752 KiB  
Article
Robotic Cell Printing for Constructing Living Yeast Cell Microarrays in Microfluidic Chips
Fermentation 2020, 6(1), 26; https://doi.org/10.3390/fermentation6010026 - 14 Feb 2020
Cited by 4 | Viewed by 3818
Abstract
Living cell microarrays in microfluidic chips allow the non-invasive multiplexed molecular analysis of single cells. Here, we developed a simple and affordable perfusion microfluidic chip containing a living yeast cell array composed of a population of cell variants (green fluorescent protein (GFP)-tagged Saccharomyces [...] Read more.
Living cell microarrays in microfluidic chips allow the non-invasive multiplexed molecular analysis of single cells. Here, we developed a simple and affordable perfusion microfluidic chip containing a living yeast cell array composed of a population of cell variants (green fluorescent protein (GFP)-tagged Saccharomyces cerevisiae clones). We combined mechanical patterning in 102 microwells and robotic piezoelectric cell dispensing in the microwells to construct the cell arrays. Robotic yeast cell dispensing of a yeast collection from a multiwell plate to the microfluidic chip microwells was optimized. The developed microfluidic chip and procedure were validated by observing the growth of GFP-tagged yeast clones that are linked to the cell cycle by time-lapse fluorescence microscopy over a few generations. The developed microfluidic technology has the potential to be easily upscaled to a high-density cell array allowing us to perform dynamic proteomics and localizomics experiments. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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9 pages, 1765 KiB  
Communication
Adaptive Evolution of Industrial Brewer’s Yeast Strains towards a Snowflake Phenotype
Fermentation 2020, 6(1), 20; https://doi.org/10.3390/fermentation6010020 - 05 Feb 2020
Cited by 7 | Viewed by 4545
Abstract
Flocculation or cell aggregation is a well-appreciated characteristic of industrial brewer’s strains, since it allows removal of the cells from the beer in a cost-efficient and environmentally-friendly manner. However, many industrial strains are non-flocculent and genetic interference to increase the flocculation characteristics are [...] Read more.
Flocculation or cell aggregation is a well-appreciated characteristic of industrial brewer’s strains, since it allows removal of the cells from the beer in a cost-efficient and environmentally-friendly manner. However, many industrial strains are non-flocculent and genetic interference to increase the flocculation characteristics are not appreciated by the consumers. We applied adaptive laboratory evolution (ALE) to three non-flocculent, industrial Saccharomyces cerevisiae brewer’s strains using small continuous bioreactors (ministats) to obtain an aggregative phenotype, i.e., the “snowflake” phenotype. These aggregates could increase yeast sedimentation considerably. We evaluated the performance of these evolved strains and their produced flavor during lab scale beer fermentations. The small aggregates did not result in a premature sedimentation during the fermentation and did not result in major flavor changes of the produced beer. These results show that ALE could be used to increase the sedimentation behavior of non-flocculent brewer’s strains. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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16 pages, 2802 KiB  
Article
Antioxidant Properties of Fermented Green Coffee Beans with Wickerhamomyces anomalus (Strain KNU18Y3)
Fermentation 2020, 6(1), 18; https://doi.org/10.3390/fermentation6010018 - 28 Jan 2020
Cited by 9 | Viewed by 5371
Abstract
A few yeast species have been tested frequently to improve the tastes, flavors, and other important quality parameters of coffee. However, continuing evaluations of different yeast species for fermenting green coffee beans will have a significant positive contribution to the coffee industry. This [...] Read more.
A few yeast species have been tested frequently to improve the tastes, flavors, and other important quality parameters of coffee. However, continuing evaluations of different yeast species for fermenting green coffee beans will have a significant positive contribution to the coffee industry. This experiment was conducted to evaluate the antioxidant properties, total phenol content (TPC), total flavonoid content (TFC), total tannin content (TTC), and the consumer acceptability of fermented green coffee beans with Wickerhamomyces anomalu. The coffee beans were roasted at different roasting conditions (light, medium, and dark). There was no significant (p > 0.05) difference between the yeast-fermented and non-fermented coffee with regard to the oxygen radical absorbance capacity (ORAC) values in medium and dark roasted coffee. Similarly, the superoxide dismutase-like (SOD)-like activity did not significantly differ in all roasting conditions. However, the SOD-like activity was significantly different (p < 0.05), particularly within light roasted and medium roasted, and between light roasted and dark roasted in both the control and fermented coffee extracts. The 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and ferric reducing antioxidant power (FRAP) were improved in fermented coffee beans. There was a significant (p ≤ 0.05) difference between the yeast-fermented and non-fermented coffee with respect to the TPC and TFC in all roasting types and the TTC in the light and dark roasting conditions. The fermentation of green coffee beans with W. anomalus increased the TPC and TFC. However, the TTC was lower in the fermented coffee beans compared to the non-fermented coffee beans in medium and dark roasted coffee. In general, fermentation of green coffee beans with W. anomalus has the potential to improve the functionality of coffee beans. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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13 pages, 1825 KiB  
Article
Co-Existence of Inoculated Yeast and Lactic Acid Bacteria and Their Impact on the Aroma Profile and Sensory Traits of Tempranillo Red Wine
Fermentation 2020, 6(1), 17; https://doi.org/10.3390/fermentation6010017 - 25 Jan 2020
Cited by 11 | Viewed by 4437
Abstract
This study investigates the effects of simultaneous inoculation of a selected Saccharomyces cerevisiae yeast strain with two different commercial strains of wine bacteria Oenococcus oeni at the beginning of the alcoholic fermentation on the kinetics of malolactic fermentation (MLF), wine chemical composition, and [...] Read more.
This study investigates the effects of simultaneous inoculation of a selected Saccharomyces cerevisiae yeast strain with two different commercial strains of wine bacteria Oenococcus oeni at the beginning of the alcoholic fermentation on the kinetics of malolactic fermentation (MLF), wine chemical composition, and organoleptic characteristics in comparison with spontaneous MLF in Tempranillo grape must from Castilla-La Mancha (Spain). Evolution of MLF was assessed by the periodic analysis of L-malic acid through the enzymatic method, and most common physiochemical parameters and sensory traits were evaluated using a standardized sensory analysis. The samples were analyzed by GC/MS in SCAN mode using a Trace GC gas chromatograph and a DSQII quadrupole mass analyzer. Co-inoculation reduced the overall fermentation time by up to 2 weeks leading to a lower increase in volatile acidity. The fermentation-derived wine volatiles profile was distinct between the co-inoculated wines and spontaneous MLF and was influenced by the selected wine bacteria used in co-inoculation. Co-inoculation allows MLF to develop under reductive conditions and results in wines with very few lactic and buttery flavors, which is related to the impact of specific compounds like 2,3-butanedione. This compound has been also confirmed as being dependent on the wine bacteria used. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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11 pages, 1393 KiB  
Article
Characterization of Old Wine Yeasts Kept for Decades under a Zero-Emission Maintenance Regime
Fermentation 2020, 6(1), 9; https://doi.org/10.3390/fermentation6010009 - 11 Jan 2020
Cited by 4 | Viewed by 4657
Abstract
All laboratories dealing with microbes have to develop a strain maintenance regime. While lyophilization based on freeze-drying may be feasible for large stock centers, laboratories around the world rely on cryopreservation and freezing of stocks at −80 °C. Keeping stocks at these low [...] Read more.
All laboratories dealing with microbes have to develop a strain maintenance regime. While lyophilization based on freeze-drying may be feasible for large stock centers, laboratories around the world rely on cryopreservation and freezing of stocks at −80 °C. Keeping stocks at these low temperatures requires investments of several thousand kW/h per year. We have kept yeast stocks for several decades at room temperature on agar slants in glass reagent tubes covered with vaspar and sealed with cotton plugs. They were part of the Geisenheim Yeast Breeding Center stock collection that was started in the 19th century, well before −80 °C refrigeration technology was invented. Of these stocks, 60 tubes were analyzed and around one-third of them could be regrown. The strains were typed by sequencing of rDNA PCR fragments. Based on BlastN analyses, twelve of the strains could be assigned to Saccharomyces cerevisiae, two to S. kudriavzevii, and the others to Meyerozyma and Candida. The strains were used in white wine fermentations and compared to standard wine yeasts Uvaferm/GHM (Geisenheim) and Lalvin EC1118. Even with added nitrogen, the strains exhibited diverse fermentation curves. Post-fermentation aroma analyses and the determination of residual sugar and organic acid concentrations indicated that some strains harbor interesting flavor characteristics, surpassing current standard yeast strains. Thus, old strain collections bear treasures for direct use either in wine fermentations or for incorporation in yeast breeding programs aimed at improving modern wine yeasts. Furthermore, this provides evidence that low-cost/long-term culture maintenance at zero-emission levels is feasible. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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9 pages, 1645 KiB  
Article
Evolution of Aromatic Profile of Torulaspora delbrueckii Mixed Fermentation at Microbrewery Plant
Fermentation 2020, 6(1), 7; https://doi.org/10.3390/fermentation6010007 - 08 Jan 2020
Cited by 15 | Viewed by 2977
Abstract
Nowadays, consumers require quality beer with peculiar organoleptic characteristics and fermentation management has a fundamental role in the production of aromatic compounds and in the overall beer quality. A strategy to achieve this goal is the use of non-conventional yeasts. In this context, [...] Read more.
Nowadays, consumers require quality beer with peculiar organoleptic characteristics and fermentation management has a fundamental role in the production of aromatic compounds and in the overall beer quality. A strategy to achieve this goal is the use of non-conventional yeasts. In this context, the use of Torulaspora delbrueckii was proposed in the brewing process as a suitable strain to obtain a product with a distinctive aromatic taste. In the present work, Saccharomyces cerevisiae/T. delbrueckii mixed fermentation was investigated at a microbrewery plant monitoring the evolution of the main aromatic compounds. The results indicated a suitable behavior of this non-conventional yeast in a production plant. Indeed, the duration of the process was very closed to that exhibited by S. cerevisiae pure fermentation. Moreover, mixed fermentation showed an increase of some aromatic compounds as ethyl hexanoate, α-terpineol, and β-phenyl ethanol. The enhancement of aromatic compounds was confirmed by the sensory evaluation carried out by trained testers. Indeed, the beers produced by mixed fermentation showed an emphasized note of fruity/citric and fruity/esters notes and did not show aroma defects. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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14 pages, 1279 KiB  
Article
Identification of Yeasts with Mass Spectrometry during Wine Production
Fermentation 2020, 6(1), 5; https://doi.org/10.3390/fermentation6010005 - 07 Jan 2020
Cited by 8 | Viewed by 3736
Abstract
The aim of the present study was to identify yeasts in grape, new wine “federweisser” and unfiltered wine samples. A total amount of 30 grapes, 30 new wine samples and 30 wine samples (15 white and 15 red) were collected from August until [...] Read more.
The aim of the present study was to identify yeasts in grape, new wine “federweisser” and unfiltered wine samples. A total amount of 30 grapes, 30 new wine samples and 30 wine samples (15 white and 15 red) were collected from August until September, 2018, from a local Slovak winemaker, including Green Veltliner (3), Mūller Thurgau (3), Palava (3), Rhein Riesling (3), Sauvignon Blanc (3), Alibernet (3), André (3), Blue Frankish (3), Cabernet Sauvignon (3), and Dornfelder (3) grapes; federweisser and unfiltered wine samples were also used in our study. Wort agar (WA), yeast extract peptone dextrose agar (YPDA), malt extract agar (MEA) and Sabouraud dextrose agar (SDA) were used for microbiological testing of yeasts. MALDI-TOF Mass Spectrometry (Microflex LT/SH) (Bruker Daltonics, Germany) was used for the identification of yeasts. A total of 1668 isolates were identified with mass spectrometry. The most isolated species from the grapes was Hanseniaspora uvarum, and from federweisser and the wine—Saccharomyces cerevisiae. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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15 pages, 1986 KiB  
Article
Ustilago Rabenhorstiana—An Alternative Natural Itaconic Acid Producer
Fermentation 2020, 6(1), 4; https://doi.org/10.3390/fermentation6010004 - 02 Jan 2020
Cited by 22 | Viewed by 3380
Abstract
Itaconic acid is an industrial produced chemical by the sensitive filamentous fungus Aspergillus terreus and can replace petrochemical-based monomers for polymer industry. To produce itaconic acid with alternative renewable substrates, such as lignocellulosic based hydrolysates, a robust microorganism is needed due to varying [...] Read more.
Itaconic acid is an industrial produced chemical by the sensitive filamentous fungus Aspergillus terreus and can replace petrochemical-based monomers for polymer industry. To produce itaconic acid with alternative renewable substrates, such as lignocellulosic based hydrolysates, a robust microorganism is needed due to varying compositions and impurities. Itaconic acid producing basidiomycetous yeasts of the family Ustilaginaceae provide this required characteristic and the species Ustilago rabenhorstiana was examined in this study. By an optimization of media components, process parameters, and a fed-batch mode with glucose the final titer increased from maximum 33.3 g·L−1 in shake flasks to 50.3 g·L−1 in a bioreactor. Moreover, itaconic acid was produced from different sugar monomers based on renewable feedstocks by U. rabenhorstiana and the robustness against weak acids as sugar degradation products was confirmed. Based on these findings, U. rabenhorstiana has a high potential as alternative natural itaconic acid producer besides the well-known U. maydis and A. terreus. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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24 pages, 3483 KiB  
Article
Screening and Application of Cyberlindnera Yeasts to Produce a Fruity, Non-Alcoholic Beer
Fermentation 2019, 5(4), 103; https://doi.org/10.3390/fermentation5040103 - 17 Dec 2019
Cited by 28 | Viewed by 7954
Abstract
Non-alcoholic beer (NAB) is enjoying growing demand and popularity due to consumer lifestyle trends and improved production methods. In recent years in particular, research into the application of non-Saccharomyces yeasts to produce NAB via limited fermentation has gained momentum. Non-Saccharomyces yeasts [...] Read more.
Non-alcoholic beer (NAB) is enjoying growing demand and popularity due to consumer lifestyle trends and improved production methods. In recent years in particular, research into the application of non-Saccharomyces yeasts to produce NAB via limited fermentation has gained momentum. Non-Saccharomyces yeasts are known to produce fruity aromas, owing to a high ester production. This trait could be harnessed to mask the often-criticized wort-like off-flavor of NAB produced via limited fermentation. Six Cyberlindnera strains were characterized and screened in wort extract. Four of the six strains produced a pleasant, fruity aroma while exhibiting low ethanol production. The strain Cyberlindnera subsufficiens C6.1 was chosen for fermentation optimization via response surface methodology (RSM) and a pilot-scale (60 L) brewing trial with subsequent sensory evaluation. A low fermentation temperature and low pitching rate enhanced the fruitiness and overall acceptance of the NAB. The NAB (0.36% ABV) produced on pilot-scale was significantly more fruity and exhibited a significantly reduced wort-like off-flavor compared to two commercial NABs. This study demonstrated the suitability of Cyberlindnera subsufficiens to produce a fruity NAB, which can compete with commercial NABs. The outcome strengthens the position of non-Saccharomyces yeasts as a serious and applicable alternative to established methods in NAB brewing. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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15 pages, 2605 KiB  
Article
The Use of CRISPR-Cas9 Genome Editing to Determine the Importance of Glycerol Uptake in Wine Yeast During Icewine Fermentation
Fermentation 2019, 5(4), 93; https://doi.org/10.3390/fermentation5040093 - 30 Oct 2019
Cited by 15 | Viewed by 5147
Abstract
The high concentration of sugars in Icewine juice causes formidable stress for the fermenting Saccharomyces cerevisiae, causing cells to lose water and shrink in size. Yeast can combat this stress by increasing the internal concentration of glycerol by activating the high osmolarity glycerol [...] Read more.
The high concentration of sugars in Icewine juice causes formidable stress for the fermenting Saccharomyces cerevisiae, causing cells to lose water and shrink in size. Yeast can combat this stress by increasing the internal concentration of glycerol by activating the high osmolarity glycerol response to synthesize glycerol and by actively transporting glycerol into the cell from the environment. The H+/glycerol symporter, Stl1p, has been previously characterized as being glucose repressed and inactivated, despite osmotic stress induction. To further investigate the role of Stl1p in Icewine fermentations, we developed a rapid single plasmid CRISPR-Cas9-based genome editing method to construct a strain of the common Icewine yeast, S. cerevisiae K1-V1116, that lacks STL1. In an Icewine fermentation, the ∆STL1 strain had reduced fermentation performance, and elevated glycerol and acetic acid production compared to the parent. These results demonstrate that glycerol uptake by Stl1p has a significant role during osmotically challenging Icewine fermentations in K1-V1116 despite potential glucose downregulation. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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17 pages, 755 KiB  
Article
Effect of Co-Inoculation with Pichia fermentans and Pediococcus acidilactici on Metabolite Produced During Fermentation and Volatile Composition of Coffee Beans
Fermentation 2019, 5(3), 67; https://doi.org/10.3390/fermentation5030067 - 22 Jul 2019
Cited by 33 | Viewed by 6553
Abstract
Removal of the mucilage layer of coffee fruits by a fermentation process has became an interesting strategy to improve coffee quality, which is able to assist the formation of flavored molecules. In this study, four sets of inoculation protocols were evaluated using ripe [...] Read more.
Removal of the mucilage layer of coffee fruits by a fermentation process has became an interesting strategy to improve coffee quality, which is able to assist the formation of flavored molecules. In this study, four sets of inoculation protocols were evaluated using ripe and immature coffee fruits, respectively, including (i) pure culture fermentation with Pichia fermentans, (ii) pure culture fermentation with Pediococcus acidilactici, (ii) combined fermentation with P. fermentans and P. acidilactici, and (iv) spontaneous, non-inoculated control. The initial pulp sugar concentration of ripe coffee fruits (0.57 and 1.13 g/L glucose and fructose content, respectively) was significantly higher than immature coffee pulp (0.13 and 0.26 g/L glucose and fructose content, respectively). Combined inoculation with P. fermentans and P. acidilactici of ripe coffee beans increased pulp sugar consumption and production of metabolites (lactic acid, ethanol, and ethyl acetate), evidencing a positive synergic interaction between these two microbial groups. On the other hand, when immature coffee fruits were used, only pure culture inoculation with P. fermentans was able to improve metabolite formation during fermentation, while combined treatment showed no significant effect. Altogether, 30 volatile compounds were identified and semi-quantified with HS- solid phase microextraction (SPME)-gas chromatography coupled to mass spectrophotometry (GC/MS) in fermented coffee beans. In comparison with pure cultures and spontaneous process, combined treatment prominently enhanced the aroma complexity of ripe coffee beans, with a sharp increase in benzeneacetaldehyde, 2-heptanol, and benzylalcohol. Consistent with the monitoring of the fermentation process, only P. fermentans treatment was able to impact the volatile composition of immature coffee beans. The major impacted compounds were 2-hexanol, nonanal, and D-limonene. In summary, this study demonstrated the great potential of the combined use of yeast and lactic acid bacteria to improve fermentation efficiency and to positively influence the chemical composition of coffee beans. Further studies are still required to investigate the mechanisms of synergism between these two microbial groups during the fermentation process and influence the sensory properties of coffee products. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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Review

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12 pages, 940 KiB  
Review
The Xylose Metabolizing Yeast Spathaspora passalidarum is a Promising Genetic Treasure for Improving Bioethanol Production
Fermentation 2020, 6(1), 33; https://doi.org/10.3390/fermentation6010033 - 18 Mar 2020
Cited by 28 | Viewed by 6765
Abstract
Currently, the fermentation technology for recycling agriculture waste for generation of alternative renewable biofuels is getting more and more attention because of the environmental merits of biofuels for decreasing the rapid rise of greenhouse gas effects compared to petrochemical, keeping in mind the [...] Read more.
Currently, the fermentation technology for recycling agriculture waste for generation of alternative renewable biofuels is getting more and more attention because of the environmental merits of biofuels for decreasing the rapid rise of greenhouse gas effects compared to petrochemical, keeping in mind the increase of petrol cost and the exhaustion of limited petroleum resources. One of widely used biofuels is bioethanol, and the use of yeasts for commercial fermentation of cellulosic and hemicellulosic agricultural biomasses is one of the growing biotechnological trends for bioethanol production. Effective fermentation and assimilation of xylose, the major pentose sugar element of plant cell walls and the second most abundant carbohydrate, is a bottleneck step towards a robust biofuel production from agricultural waste materials. Hence, several attempts were implemented to engineer the conventional Saccharomyces cerevisiae yeast to transport and ferment xylose because naturally it does not use xylose, using genetic materials of Pichia stipitis, the pioneer native xylose fermenting yeast. Recently, the nonconventional yeast Spathaspora passalidarum appeared as a founder member of a new small group of yeasts that, like Pichia stipitis, can utilize and ferment xylose. Therefore, the understanding of the molecular mechanisms regulating the xylose assimilation in such pentose fermenting yeasts will enable us to eliminate the obstacles in the biofuels pipeline, and to develop industrial strains by means of genetic engineering to increase the availability of renewable biofuel products from agricultural biomass. In this review, we will highlight the recent advances in the field of native xylose metabolizing yeasts, with special emphasis on S. passalidarum for improving bioethanol production. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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19 pages, 1394 KiB  
Review
Modulating Wine Pleasantness Throughout Wine-Yeast Co-Inoculation or Sequential Inoculation
Fermentation 2020, 6(1), 22; https://doi.org/10.3390/fermentation6010022 - 09 Feb 2020
Cited by 19 | Viewed by 8725
Abstract
Wine sensory experience includes flavor, aroma, color, and (for some) even acoustic traits, which impact consumer acceptance. The quality of the wine can be negatively impacted by the presence of off-flavors and aromas, or dubious colors, or sediments present in the bottle or [...] Read more.
Wine sensory experience includes flavor, aroma, color, and (for some) even acoustic traits, which impact consumer acceptance. The quality of the wine can be negatively impacted by the presence of off-flavors and aromas, or dubious colors, or sediments present in the bottle or glass, after pouring (coloring matter that precipitates or calcium bitartrate crystals). Flavor profiles of wines are the result of a vast number of variations in vineyard and winery production, including grape selection, winemaker’s knowledge and technique, and tools used to produce wines with a specific flavor. Wine color, besides being provided by the grape varieties, can also be manipulated during the winemaking. One of the most important “tools” for modulating flavor and color in wines is the choice of the yeasts. During alcoholic fermentation, the wine yeasts extract and metabolize compounds from the grape must by modifying grape-derived molecules, producing flavor-active compounds, and promoting the formation of stable pigments by the production and release of fermentative metabolites that affect the formation of vitisin A and B type pyranoanthocyanins. This review covers the role of Saccharomyces and non-Saccharomyces yeasts, as well as lactic acid bacteria, on the perceived flavor and color of wines and the choice that winemakers can make by choosing to perform co-inoculation or sequential inoculation, a choice that will help them to achieve the best performance in enhancing these wine sensory qualities, avoiding spoilage and the production of defective flavor or color compounds. Full article
(This article belongs to the Special Issue Yeast Biotechnology 3.0)
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