Non-Conventional Yeasts in Fermentation Processes: Potentialities and Limitations (original) (raw)
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FEMS Yeast Research, 2015
Saccharomyces cerevisiae has been used for millennia in the production of food and beverages and is by far the most studied yeast species. Currently, it is also the most used microorganism in the production of first-generation bioethanol from sugar or starch crops. Second-generation bioethanol, on the other hand, is produced from lignocellulosic feedstocks that are pretreated and hydrolyzed to obtain monomeric sugars, mainly D-glucose, D-xylose and L-arabinose. Recently, S. cerevisiae recombinant strains capable of fermenting pentose sugars have been generated. However, the pretreatment of the biomass results in hydrolysates with high osmolarity and high concentrations of inhibitors. These compounds negatively influence the fermentation process. Therefore, robust strains with high stress tolerance are required. Up to now, more than 2000 yeast species have been described and some of these could provide a solution to these limitations because of their high tolerance to the most predominant stress conditions present in a second-generation bioethanol reactor. In this review, we will summarize what is known about the non-conventional yeast species showing unusual tolerance to these stresses, namely Zygosaccharomyces rouxii (osmotolerance), Kluyveromyces marxianus and Ogataea (Hansenula) polymorpha (thermotolerance), Dekkera bruxellensis (ethanol tolerance), Pichia kudriavzevii (furan derivatives tolerance) and Z. bailii (acetic acid tolerance).
Non-conventional Yeasts: from Basic Research to Application
2019
Biodiesel production is a fast-growing industry. Biodiesel is obtained through transesterification of different kinds of oils with methanol. This process results in a formation of substantial amounts (up to 10% of a total product mass) of the by-product fraction that mainly contains glycerol but also some toxic contaminations (spent catalyst, salts after neutralization, residual methanol, methyl esters, and free fatty acids), and that is therefore called crude glycerol. Efficient utilization of this fraction is imperative to the sustainability of the biodiesel industry. This review describes different methods of valorization of the crude glycerol fraction with the focus on biotechnological processes conducted by yeasts. In particular, production of organic acids, polyols, ethanol, microbial oil, carotenoids, γ-decalactone, sophorolipids, heterologous proteins, and biomass is discussed. Keywords Biodiesel • Crude glycerol • Yarrowia lipolytica • Pichia pastoris • Oleaginous yeasts • Citric acid • Erythritol • SCO • Ethanol • Carotenoids 12.1 Biodiesel as an Emerging Sustainable Biofuel Global warming (caused by increased carbon dioxide emissions), environmental pollution, and the threat of exhaustion of world resources of fossil fuels are some of the many concerns that had arisen in twentieth century and followed humanity into the new millennium.
Non-conventional yeasts for food and additives production in a circular economy perspective
FEMS Yeast Research, 2021
Yeast species have been spontaneously participating in food production for millennia, but the scope of applications was greatly expanded since their key role in beer and wine fermentations was clearly acknowledged. The workhorse for industry and scientific research has always been Saccharomyces cerevisiae. It occupies the largest share of the dynamic yeast market, that could further increase thanks to the better exploitation of other yeast species. Food-related ‘non-conventional’ yeasts (NCY) represent a treasure trove for bioprospecting, with their huge untapped potential related to a great diversity of metabolic capabilities linked to niche adaptations. They are at the crossroad of bioprocesses and biorefineries, characterized by low biosafety risk and produce food and additives, being also able to contribute to production of building blocks and energy recovered from the generated waste and by-products. Considering that the usual pattern for bioprocess development focuses on singl...
Conventional and Non-Conventional Yeasts in Beer Production
Fermentation
The quality of beer relies on the activity of fermenting yeasts, not only for their good fermentation yield-efficiency, but also for their influence on beer aroma, since most of the aromatic compounds are intermediate metabolites and by-products of yeast metabolism. Beer production is a traditional process, in which Saccharomyces is the sole microbial component, and any deviation is considered a flaw. However, nowadays the brewing sector is faced with an increasing demand for innovative products, and it is diffusing the use of uncharacterized autochthonous starter cultures, spontaneous fermentation, or non-Saccharomyces starters, which leads to the production of distinctive and unusual products. Attempts to obtain products with more complex sensory characteristics have led one to prospect for non-conventional yeasts, i.e., non-Saccharomyces yeasts. These generally are characterized by low fermentation yields and are more sensitive to ethanol stress, but they provide a distinctive aroma and flavor. Furthermore, non-conventional yeasts can be used for the production of low-alcohol/non-alcoholic and light beers. This review aims to present the main findings about the role of traditional and non-conventional yeasts in brewing, demonstrating the wide choice of available yeasts, which represents a new biotechnological approach with which to target the characteristics of beer and to produce different or even totally new beer styles.
Exploitation of Three Non-Conventional Yeast Species in the Brewing Process
Microorganisms
Consumers require high-quality beers with specific enhanced flavor profiles and non-conventional yeasts could represent a large source of bioflavoring diversity to obtain new beer styles. In this work, we investigated the use of three different non-conventional yeasts belonging to Lachancea thermotolerans, Wickerhamomyces anomalus, and Zygotorulaspora florentina species in pure and mixed fermentation with the Saccharomyces cerevisiae commercial starter US-05. All three non-conventional yeasts were competitive in co-cultures with the S. cerevisiae, and they dominated fermentations with 1:20 ratio (S. cerevisiae/non-conventional yeasts ratios). Pure non-conventional yeasts and co-cultures affected significantly the beer aroma. A general reduction in acetaldehyde content in all mixed fermentations was found. L. thermotolerans and Z. florentina in mixed and W. anomalus in pure cultures increased higher alcohols. L. thermotolerans led to a large reduction in pH value, producing, in pure ...
In the present study fourteen cultures were isolated from soil samples, fruits and fermented products, of which seven were found to be yeasts. These seven yeasts were subjected to thorough identification scheme upto species level by cultural, morphological, microscopic, biochemical and physiological studies and by comparing the results with reference strain Saccharomyces cerevisiae MTCC 170. The yeasts were characterized with respect to temperature tolerance, ethanol tolerance and osmotolerance. Batch stationary fermentation was carried out in Erlenmeyer flasks for bioethanol production. Growth and fermentation kinetics were calculated for stationary fermentation. Three species (TA, C2 and K2) were identified as Saccharomyces cerevisiae, two (S1 and S2) were identified as Saccharomyces rosinii, and the other two (K1 and S3) were identified as Saccharomyces exiguus and Rhodotorula minuta respectively. Among all yeasts Saccharomyces cerevisiae TA and C2 strains were high ethanol tolerant (tolerated 14% ethanol), high osmotolerant (tolerated 20% sugar) and high bioethanol producing strains with a yield of 32 and 28 g/l for TA and C2 respectively. Results indicated that fermentation kinetics with S. cerevisiae TA and C2 strains were faster than other yeast strains including the reference strain MTCC 170 with the ethanol yield (Yp/s= 0.160 and 0.155 g g-1), volumetric substrate uptake (QS= 2.638 and 2.50 g L-1 h-1), conversion rate into ethanol (16.80 and 15.50 %) and volumetric product productivity (Qp,= 0.44 and 0.38 g L-1 h- 1) respectively.
Taming wild yeast: potential of conventional and nonconventional yeasts in industrial fermentations
Annual review of microbiology, 2014
Yeasts are the main driving force behind several industrial food fermentation processes, including the production of beer, wine, sake, bread, and chocolate. Historically, these processes developed from uncontrolled, spontaneous fermentation reactions that rely on a complex mixture of microbes present in the environment. Because such spontaneous processes are generally inconsistent and inefficient and often lead to the formation of off-flavors, most of today's industrial production utilizes defined starter cultures, often consisting of a specific domesticated strain of Saccharomyces cerevisiae, S. bayanus, or S. pastorianus. Although this practice greatly improved process consistency, efficiency, and overall quality, it also limited the sensorial complexity of the end product. In this review, we discuss how Saccharomyces yeasts were domesticated to become the main workhorse of food fermentations, and we investigate the potential and selection of nonconventional yeasts that are of...
Assessing the potential of wild yeasts for bioethanol production
Journal of Industrial Microbiology & Biotechnology, 2014
Bioethanol fermentations expose yeasts to a new, complex and challenging fermentation medium with specific inhibitors and sugar mixtures depending on the type of carbon source. It is therefore suggested that the natural diversity of yeasts should be further exploited in order to find yeasts with good ethanol yield in stressed fermentation media. In this study, we screened more than 50 yeast isolates of which we selected 5 isolates with promising features. The species Candida bombi, Wickerhamomyces anomalus and Torulaspora delbrueckii showed better osmo-and hydroxymethylfurfural tolerance than Saccharomyces cerevisiae. However, S. cerevisiae isolates had the highest ethanol yield in fermentation experiments mimicking high gravity fermentations (25% glucose) and artificial lignocellulose hydrolysates (with a myriad of inhibitors). Interestingly, among two tested S. cerevisiae strains, a wild strain isolated from an oak tree performed better than Ethanol Red, a S. cerevisiae strain which is currently commonly used in industrial bioethanol fermentations. Additionally, a W. anomalus strain isolated from sugar beet thick juice was found to have a comparable ethanol yield, but needed longer fermentation time. Other non-Saccharomyces yeasts yielded lower ethanol amounts.
Non-conventional Yeast cell factories for sustainable bioprocesses
FEMS microbiology letters, 2018
The non-conventional yeasts Kluyveromyces lactis, Yarrowia lipolytica, Ogataea polymorpha and Pichia pastoris have been developed as eukaryotic expression hosts because of their desirable growth characteristics, including inhibitor and thermo-tolerance, utilization of diverse carbon substrates, and high amount of extracellular protein secretion. These yeasts already have established in the heterologous production of vaccines, therapeutic proteins, food additives, and bio-renewable chemicals, but recent advances in genetic tool box have the potential to greatly expand and diversify their impact on biotechnology. The diversity of these yeasts includes many strains possessing highly useful, and in some cases even uncommon, metabolic capabilities potentially helpful for bioprocess industry. This review outlines the recent updates of non-conventional yeast in sustainable bioprocesses.