Non-saccharomyces yeast probiotics: revealing relevance and potential

Non-Saccharomyces yeasts are unicellular eukaryotes that play important roles in diverse ecological niches. In recent decades, their physiological and morphological properties have been reevaluated and reassessed, demonstrating the enormous potential they possess in various fields of application. Non-Saccharomyces yeasts have gained relevance as probiotics, and in vitro and in vivo assays are very promising and offer a research niche with novel applications within the functional food and nutraceutical industry. Several beneficial effects have been described, such as antimicrobial and antioxidant activities and gastrointestinal modulation and regulation functions. In addition, several positive effects of bioactive compounds or production of specific enzymes have been reported on physical, mental and neurodegenerative diseases as well as on the organoleptic properties of the final product. Other points to highlight are the multiomics as a tool to enhance characteristics of interest within the industry; as well as microencapsulation offer a wide field of study that opens the niche of food matrices as carriers of probiotics; in turn, non-Saccharomyces yeasts offer an interesting alternative as microencapsulating cells of various compounds of interest.

Preservation of non-Saccharomyces yeasts: Current technologies and challenges

There is a recent and growing interest in the study and application of non-Saccharomyces yeasts, mainly in fermented foods. Numerous publications and patents show the importance of these yeasts. However, a fundamental issue in studying and applying them is to ensure an appropriate preservation scheme that allows to the non-Saccharomyces yeasts conserve their characteristics and fermentative capabilities by long periods of time. The main objective of this review is to present and analyze the techniques available to preserve these yeasts (by conventional and non-conventional methods), in small or large quantities for laboratory or industrial applications, respectively. Wine fermentation is one of the few industrial applications of non-Saccharomyces yeasts, but the preservation stage has been a major obstacle to achieve a wider application of these yeasts. This review considers the preservation techniques, and clearly defines parameters such as culturability, viability, vitality and robustness. Several conservation strategies published in research articles as well as patents are analyzed, and the advantages and disadvantages of each technique used are discussed. Another important issue during conservation processes is the stress to which yeasts are subjected at the time of preservation (mainly oxidative stress). There is little published information on the subject for non-Saccharomyces yeast, but it is a fundamental point to consider when designing a preservation strategy.

Wine yeast peroxiredoxin TSA1 plays a role in growth, stress response and trehalose metabolism in biomass propagation

Peroxiredoxins are a family of peroxide-degrading enzymes for challenging oxidative stress. They receive their reducing power from redox-controlling proteins called thioredoxins, and these, in turn, from thioredoxin reductase. The main cytosolic peroxiredoxin is Tsa1, a moonlighting protein that also acts as protein chaperone a redox switch controlling some metabolic events. Gene deletion of peroxiredoxins in wine yeasts indicate that TSA1, thioredoxins and thioredoxin reductase TRR1 are required for normal growth in medium with glucose and sucrose as carbon sources. TSA1 gene deletion also diminishes growth in molasses, both in flasks and bioreactors. The TSA1 mutation brings about an expected change in redox parameters but, interestingly, it also triggers a variety of metabolic changes. It influences trehalose accumulation, lowering it in first molasses growth stages, but increasing it at the end of batch growth, when respiratory metabolism is set up. Glycogen accumulation at the entry of the stationary phase also increases in the tsa1Δ mutant. The mutation reduces fermentative capacity in grape juice, but the vinification profile does not significantly change. However, acetic acid and acetaldehyde production decrease when TSA1 is absent. Hence, TSA1 plays a role in the regulation of metabolic reactions leading to the production of such relevant enological molecules.

Basal catalase activity and high glutathione levels influence the performance of non-Saccharomyces active dry wine yeasts

Non-Saccharomyces wine yeasts are useful tools for producing wines with complex aromas or low ethanol content. Their use in wine would benefit from their production as active dry yeast (ADY) starters to be used as co-inocula alongside S. cerevisiae. Oxidative stress during biomass propagation and dehydration is a key factor in determining ADY performance, as it affects yeast vitality and viability. Several studies have analysed the response of S. cerevisiae to oxidative stress under dehydration conditions, but not so many deal with non-conventional yeasts. In this work, we analysed eight non-Saccharomyces wine yeasts under biomass production conditions and studied oxidative stress parameters and lipid composition. The results revealed wide variability among species in their technological performance during ADY production. Also, for Metschnikowia pulcherrima and Starmerella bacillaris, better performance correlates with high catalase activity and glutathione levels. Our data suggest that non-Saccharomyces wine yeasts with an enhanced oxidative stress response are better suited to grow under ADY production conditions.

Highlighting Protective Effect of Encapsulation on Yeast Cell Response to Dehydration Using Synchrotron Infrared Microspectroscopy at the Single-Cell Level

In the present paper, the Layer by Layer (LbL) method using β-lactoglobulin and sodium alginate was performed to individually encapsulate Saccharomyces cerevisiae cells in microorganized shells in order to protect them against stresses during dehydration. Higher survival (∼1 log) for encapsulated yeast cells was effectively observed after air dehydration at 45°C. For the first time, the potentiality of Synchrotron-Fourier Transform InfraRed microspectroscopy (S-FTIR) was used at the single-cell level in order to analyze the contribution of the biochemical composition of non-encapsulated vs. encapsulated cells in response to dehydration. The microspectroscopy measurements clearly differentiated between non-encapsulated and encapsulated yeast cells in the amide band region. In the spectral region specific to lipids, the S-FTIR results indicated probably the decrease in membrane fluidity of yeast after dehydration without significant distinction between the two samples. These data suggested minor apparent chemical changes in cell attributable to the LbL system upon dehydration. More insights are expected regarding the lower mortality among encapsulated cells. Indeed the hypothesis that the biopolymeric layers could induce less damage in cell by affecting the transfer kinetics during dehydration-rehydration cycle, should be verified in further work.

Biophysical Stress Responses of the Yeast Lachancea thermotolerans During Dehydration Using Synchrotron-FTIR Microspectroscopy

During industrial yeast production, cells are often subjected to deleterious hydric variations during dehydration, which reduces their viability and cellular activity. This study is focused on the yeast Lachancea thermotolerans, particularly sensitive to dehydration. The aim was to understand the modifications of single-cells biophysical profiles during different dehydration conditions. Infrared spectra of individual cells were acquired before and after dehydration kinetics using synchrotron radiation-based Fourier-transform infrared (S-FTIR) microspectroscopy. The cells were previously stained with fluorescent probes in order to measure only viable and active cells prior to dehydration. In parallel, cell viability was determined using flow cytometry under identical conditions. The S-FTIR analysis indicated that cells with the lowest viability showed signs of membrane rigidification and modifications in the amide I (α-helix and β-sheet) and amide II, which are indicators of secondary protein structure conformation and degradation or disorder. Shift of symmetric C–H stretching vibration of the CH₂ group upon a higher wavenumber correlated with better cell viability, suggesting a role of plasma membrane fluidity. This was the first time that the biophysical responses of L. thermotolerans single-cells to dehydration were explored with S-FTIR. These findings are important for clarifying the mechanisms of microbial resistance to stress in order to improve the viability of sensitive yeasts during dehydration.

Mechanisms of Yeast Adaptation to Wine Fermentations

Cells face genetic and/or environmental changes in order to outlast and proliferate. Characterization of changes after stress at different "omics" levels is crucial to understand the adaptation of yeast to changing conditions. Wine fermentation is a stressful situation which yeast cells have to cope with. Genome-wide analyses extend our cellular physiology knowledge by pointing out the mechanisms that contribute to sense the stress caused by these perturbations (temperature, ethanol, sulfites, nitrogen, etc.) and related signaling pathways. The model organism, Saccharomyces cerevisiae, was studied in response to industrial stresses and changes at different cellular levels (transcriptomic, proteomic, and metabolomics), which were followed statically and/or dynamically in the short and long terms. This chapter focuses on the response of yeast cells to the diverse stress situations that occur during wine fermentations, which induce perturbations, including nutritional changes, ethanol stress, temperature stress, oxidative stress, etc.

Anticonvulsant effect of anacardic acid in murine models: Putative role of GABAergic and antioxidant mechanisms

Epilepsy is a neurological disease affecting people of all ages worldwide. Side effects of antiepileptic drugs and their association with oxidative stress stimulate the search for new drugs, which would be more affordable with fewer adverse effects. Accordingly, the aim of the present work is to evaluate the anticonvulsant effect of anacardic acid (AA), a natural compound extracted from cashew liquid (Anacardium occidentalis), in murine models, as well as its antioxidant actions in Saccharomyces cerevisiae. AA (>90% purity) was tested, in vivo, in male Swiss mice (25-30 g) with four convulsive models, (1) pentylenetetrazole, (2) pilocarpine, (3) electroshock, and (4) kainic acid, at doses of 25, 50, and 100 mg/kg, body weight (B.W.) Additionally, the effective dose, toxic dose, and protective index studies were also performed. Results revealed that AA exhibits anticonvulsive effects in models 1, 3, and 4, with a mean effective dose (ED₅₀) of 39.64 (model 1) >100 mg/kg, B.W. (model 2), and 38.36 (model 3); furthermore, AA displays a protection index of 1.49 (model 1), <0.6 (model 2, and 1.54 (model 3). In addition, AA showed antioxidant activities in S. cerevisiae mutated for superoxide dismutases (SOD). In conclusion, these results show that AA exhibits significant anticonvulsant and antioxidant activities and may be used as a promising natural product for the treatment of epilepsy.

Non-canonical regulation of glutathione and trehalose biosynthesis characterizes non-Saccharomyces wine yeasts with poor performance in active dry yeast production

Several yeast species, belonging to Saccharomyces and non-Saccharomyces genera, play fundamental roles during spontaneous must grape fermentation, and recent studies have shown that mixed fermentations, co-inoculated with S. cerevisiae and non-Saccharomyces strains, can improve wine organoleptic properties. During active dry yeast (ADY) production, antioxidant systems play an essential role in yeast survival and vitality as both biomass propagation and dehydration cause cellular oxidative stress and negatively affect technological performance. Mechanisms for adaptation and resistance to desiccation have been described for S. cerevisiae, but no data are available on the physiology and oxidative stress response of non-Saccharomyces wine yeasts and their potential impact on ADY production. In this study we analyzed the oxidative stress response in several non-Saccharomyces yeast species by measuring the activity of reactive oxygen species (ROS) scavenging enzymes, e.g., catalase and glutathione reductase, accumulation of protective metabolites, e.g., trehalose and reduced glutathione (GSH), and lipid and protein oxidation levels. Our data suggest that non-canonical regulation of glutathione and trehalose biosynthesis could cause poor fermentative performance after ADY production, as it corroborates the corrective effect of antioxidant treatments, during biomass propagation, with both pure chemicals and food-grade argan oil.

Identification by phenotypic and genetic approaches of an indigenous Saccharomyces cerevisiae wine strain with high desiccation tolerance

During active dry yeast (ADY) production process, cells are exposed to multiple stresses, such as thermal, oxidative and hyperosmotic shock. Previously, by analysing cells in exponential growth phase, we selected an indigenous Saccharomyces cerevisiae wine strain, namely CD-6Sc, for its higher tolerance to desiccation and higher expression of specific desiccation stress-related genes in comparison to other yeast strains. In this study, we performed a desiccation treatment on stationary phase cells by comparing the efficacy of two different methods: a 'laboratory dry test' on a small scale (mild stress) and a treatment by spray-drying (severe stress), one of the most appropriate preservation method for yeasts and other micro-organisms. The expression of selected desiccation-related genes has been also assessed in order to validate predictive markers for desiccation tolerance. Our data demonstrate that the 'mild' and the 'severe' desiccation treatments give similar results in terms of cell recovery, but the choice of marker genes strictly depends on the growth phase in which cells undergo desiccation. The indigenous CD-6Sc was ultimately identified as a high dehydration stress-tolerant indigenous strain suitable for ADY production. This study highlights the exploitation of natural yeast biodiversity as a source of hidden technological features and as an alternative approach to strain improvement by genetic modifications. Copyright © 2017 John Wiley & Sons, Ltd.

Comparative study of Saccharomyces cerevisiae wine strains to identify potential marker genes correlated to desiccation stress tolerance

The most diffused formulation of starter for winemaking is active dry yeast (ADY). ADYs production process is essentially characterized by air-drying stress, a combination of several stresses, including thermal, hyperosmotic and oxidative and cell capacity to counteract such multiple stresses will determine its survival. The molecular mechanisms underlying cell stress response to desiccation have been mostly studied in laboratory and commercial yeast strains, but a growing interest is currently developing for indigenous yeast strains which represent a valuable and alternative source of genetic and molecular biodiversity to be exploited. In this work, a comparative study of different Saccharomyces cerevisiae indigenous wine strains, previously selected for their technological traits, has been carried out to identify potentially relevant genes involved in desiccation stress tolerance. Cell viability was evaluated along desiccation treatment and gene expression was analyzed by real-time PCR before and during the stress. Our data show that the observed differences in individual strain sensitivity to desiccation stress could be associated to specific gene expression over time. In particular, either the basal or the stress-induced mRNA levels of certain genes, such as HSP12, SSA3, TPS1, TPS2, CTT1 and SOD1, result tightly correlated to the strain survival advantage. This study provides a reliable and sensitive method to predict desiccation stress tolerance of indigenous wine yeast strains which could be preliminary to biotechnological applications.

Food-grade argan oil supplementation in molasses enhances fermentative performance and antioxidant defenses of active dry wine yeast

The tolerance of the yeast Saccharomyces cerevisiae to desiccation is important for the use of this microorganism in the wine industry, since active dry yeast (ADY) is routinely used as starter for must fermentations. Both biomass propagation and dehydration cause cellular oxidative stress, therefore negatively affecting yeast performance. Protective treatments against oxidative damage, such as natural antioxidants, may have important biotechnological implications. In this study we analysed the antioxidant capacity of pure chemical compounds (quercetin, ascorbic acid, caffeic acid, oleic acid, and glutathione) added to molasses during biomass propagation, and we determine several oxidative damage/response parameters (lipid peroxidation, protein carbonylation, protective metabolites and enzymatic activities) to assess their molecular effects. Supplementation with ascorbic, caffeic or oleic acids diminished the oxidative damage associated to ADY production. Based on these results, we tested supplementation of molasses with argan oil, a natural food-grade ingredient rich in these three antioxidants, and we showed that it improved both biomass yield and fermentative performance of ADY. Therefore, we propose the use of natural, food-grade antioxidant ingredients, such as argan oil, in industrial processes involving high cellular oxidative stress, such as the biotechnological production of the dry starter.