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Evaluation of the Non-Conventional Yeast Starmerella Bacillaris as Biocontrol Agent and Selected Starter for Alcoholic Beverages Production
Get PDFYeasts are the main protagonists of the alcoholic fermentation and strongly influence the final characteristics of wine and other alcoholic beverages. In winemaking, during spontaneous fermentation, this process is carried out by indigenous yeasts present on the grape berry and there is a progressive growth pattern of different yeast species, with the final stages invariably being dominated by the alcohol-tolerant strains of Saccharomyces cerevisiae. This species is universally known as the ‘wine yeast’ and is widely preferred for initiating wine fermentations.
From a technological point of view spontaneous grape juice fermentations sometime become stuck or sluggish. This lack of reproducibility and predictability has favored, in the past, the use of yeast starters, generally composed of single strains of S. cerevisiae. Selected S. cerevisiae strains predominate during must fermentation, ensure rapid and reliable grape juice fermentation and, as consequence, consistent and predictable wine quality. However, there has been increasing recognition that wines made with Saccharomyces starter cultures are less complex, producing standardized wines.
In fact, during spontaneous fermentation many other species (the so call non–Saccharomyces yeasts) are present in the grape must and traditionally they were considered deleterious as responsible for some wine off-flavors. Recently, the role of non-Saccharomyces species has been re-evaluated as some of them has been proposed as co-starter to simulate natural must fermentation and to confer greater complexity and specificity to the wine.
In this context, the thesis project was developed in order to select new non-Saccharomyces yeast strains from fermenting musts of overripe grape berries. This stage of grape ripening is characterized to be more susceptible to infection of fungal pathogens such as Botrytis cinerea, whom yeasts present on the berry surface have to compete with. Thirty-six isolates were identified as Starmerella bacillaris isolated from destemmed dried grape of Raboso Piave variety, grown on Bagnoli DOC (Appellation of Origin) area (North-East of Italy). This species is recently proven to be of oenological interest mainly for its high glycerol production. Among them, 14 strains were phenotypically characterized and, for the first time, the antifungal activity of S. bacillaris species against B. cinerea and P. expansum were demonstrated. Moreover, fermentation performances of S. bacillaris strains were evaluated in synthetic, grape and apple musts (for the first time in cider production).
When tested in sequential fermentations with S. cerevisiae this yeast improved the quality of wine and cider. The obtained results indicate that S. bacillaris can be proposed as biocontrol agent on grape in vineyard and during postharvest on stored apples and its presence on fruit surface positively influences the following juice fermentation. Therefore the released of this yeast in the vineyard can increase the sustainability of the production process and the final wine quality. The obtained results provide a solid basis for a new management of yeast used for winemaking and other alcoholic beverage production and open new prospects for a more integrated strategy to increase wine quality.
Then, in this thesis, new S. bacillaris characteristics were evaluated in order to improve alcoholic beverages quality, such as mannoproteins and glutathione production. The quantification of these compounds was determined at the end of fermentation in synthetic must. S. bacillaris was proved to produce different mannoproteins with functional characteristics related to wine stability. Mannoproteins extracted from S. bacillaris cultures presented great potential in increasing the protein stabilization, while if they were produced during sequential fermentation with S. cerevisiae, enhanced the tartaric stabilization. Moreover, in this thesis, a very high glutathione content was demonstrated in S. bacillaris cells after fermentation. Therefore, yeast lees obtained from S. bacillaris fermentations can be proposed as as glutathione source.
In the last part of this thesis the aim was to understand the genomic determinants of S. bacillaris technological traits described in the previous parts. Therefore. the whole-genome sequence of two relevant S. bacillaris strains was performed. By means of genome comparisons between the two S. bacillaris strains and between S. bacillaris, S. cerevisiae and other oenological yeasts, specific genes and metabolic pathways involved in technologically-relevant traits were identified and studied
Effects of sequential fermentation using Starmerella bacillaris and Saccharomyces cerevisiae on wine colour
No full textInvestigating the glutathione accumulation by non-conventional wine yeasts in optimized growth conditions and multi-starter fermentations
Get PDFGlutathione (GSH) is the most abundant non-protein thiol in yeasts and plays an important role as antioxidant in wine. Application of selected GSH-accumulating strains can improve wine sensorial quality and stability, but most selection programs have been conducted on Saccharomyces cerevisiae. Therefore, the aim of the study was to evaluate the ability of different non-Saccharomyces yeasts, i.e. Lachancea thermotolerans, Metschnikowia spp. and Starmerella bacillaris, to produce glutathione. This feature was evaluated in an optimized medium under aerobiosis (MGSH) and in microfermentations using synthetic grape juice (SGJ) and pasteurized grape juice (PGJ), in single or sequential inoculations with S. cerevisiae. The non-Saccharomyces yeasts showed a good capacity to produce GSH, particularly Metschnikowia spp., which achieved significantly greater concentrations. As expected, the strains presented higher growth and glutathione accumulation in MGSH than in SGJ and PGJ. In the microvinification trials, GSH production was higher in PGJ than SGJ, while cell growth was similar, indicating the influence of grape juice composition on GSH metabolism. Taken together, our results demonstrated that selected non-conventional yeast strains, with proven interesting oenological traits, have a good potential to produce GSH, and thus are more suitable and worthwhile for application as active or inactivated dry yeasts preparations
Contribution of non-Saccharomyces yeasts to wine volatile and sensory diversity: A study on Lachancea thermotolerans, Metschnikowia spp. and Starmerella bacillaris strains isolated in Italy
No full textSaccharomyces cerevisiae starter cultures are largely used in winemaking to repress the wild microorganisms and achieve more predictable and desired outcomes. Notwithstanding, alternative microbial resources received increasing attention for their potential to produce wines with more distinctive and typical features. Our previous survey revealed a great inter- and intra-species diversity in an extensive collection of non-Saccharomyces wine yeasts from multiple regions of Italy. This study aimed to explore the detected biodiversity evaluating the quality of wines obtained by sequential inoculation of specific selected strains of the collection (Lachancea thermotolerans or Metschnikowia spp. or Starmerella bacillaris), and S. cerevisiae EC 1118. Fermentations of natural grape must at laboratory scale were followed by microbiological, chemical and sensorial analysis of the wines. The results indicated that each yeast species and strain exerted a distinctive impact on the wine, giving final products clearly separated with Principal Component Analysis. In particular, L. thermotolerans contributed producing relevant amounts of lactic acid and had the highest potential to reduce ethanol content; the presence of S. bacillaris increased the level of glycerol, and, remarkably, reduced acetaldehyde and total SO2; Metschnikowia spp. promoted the formation of higher alcohols and esters, and reduced volatile phenols. The sensory analysis based on the orthonasal aroma confirmed the separation between the wines obtained with the sequential fermentations and the control with single inoculation of EC 1118, although the three non-Saccharomyces species used could not be clearly distinguishable by the panelists. This study indicates that the use of selected native non-Saccharomyces strains in conjunction with S. cerevisiae positively modulates some relevant chemical parameters, and improves the aromatic intensity of wine, therefore justifying investments in non-conventional yeasts as co-starter cultures
Utilization of autochthonous strains of Metschnikowia fructicola and Metschnikowia pulcherrima to inhibit Botrytis cinerea development
No full textComplete Genome Sequence and Carbohydrates-Active EnZymes (CAZymes) Analysis of Lactobacillus paracasei DTA72, a Potential Probiotic Strain with Strong Capability to Use Inulin
No full textThe whole genome sequence of Lactobacillus paracasei DTA72, isolated from healthy infant feces, is reported, along with the Carbohydrates-Active enZymes (CAZymes) analysis and an in silico safety assessment. Strain DTA72 had previously demonstrated some interesting potential probiotic features, such as a good resistance to gastrointestinal conditions and an anti-Listeria activity. The 3.1 Mb sequenced genome consists of 3116 protein-coding sequences distributed on 340 SEED subsystems. In the present study, we analyzed the fermentation capability of strain DTA72 on six different carbohydrate sources, namely, glucose, fructose, lactose, galactose, xylose, and inulin by using phenotypical and genomic approaches. Interestingly, L. paracasei DTA72 evidenced the best growth performances on inulin with a much shorter lag phase and higher number of cells at the stationary phase in comparison with all the sugars tested. The CAZyme analysis using the predicted amino acid sequences detected 80 enzymes, distributed into the five CAZymes classes. Moreover, the in silico analysis revealed the absence of blood hemolytic genes, transmissible antibiotic resistances, and plasmids in DTA72. The results described in this study, together with those previously reported and particularly the strong capability to utilize inulin as energy source, make DTA72 a very interesting potential probiotic strain to be considered for the production of synbiotic foods. The complete genome data have been deposited in GenBank under the accession number WUJH00000000. © 2020, Springer Science+Business Media, LLC, part of Springer Nature
How Microbiome Composition Correlates with Biochemical Changes during Sauerkraut Fermentation: a Focus on Neglected Bacterial Players and Functionalities
Get PDFThis study provided a new perspective on the bacterial community succession during sauerkraut fermentation, and on resulting metabolic functions. While culture-dependent methods confirmed the key role of the well-known core microbiome species, metagenomic approach (shotgun) revealed Secundilactobacillus malefermentans as a species of the core microbiome, especially during the last weeks of fermentation. Although the potentiality of S. malefermentans has not yet fully explored, it held core functional genes usually attributed to others lactic acid bacteria driving sauerkraut fermentation. Based on our results it is arguable that S. malefermentans might have a key a role during sauerkraut fermentation carried out at low temperature. Under our experimental conditions, the profile of phenolic compounds changed throughout sauerkraut fermentation. The amount of free phenolics, including free phenolic acids, increased at the beginning of the fermentation, whereas the conversion of phenolic acids into microbial derivatives was consistent during the last part of the sauerkraut fermentation. We pioneered correlating changes in the phenolics profile to changes in the microbiome, although the framework presented is still fragmentary. Annotated genes linked to the phenolic compounds metabolism (VprA and padA) were found in many core species during the whole process. A high metabolic potential for phenolics bioconversion emerged for lactobacilli and Pediococcus spp. through correlation analysis between microbiome composition and phenolics profile. IMPORTANCE Our study was not limited to describe the succession pattern of the microbial community during sauerkraut fermentation, but also revealed how some neglected bacterial players belong to the core species during sauerkrauts processing, especially at low temperature. Such species might have a role as potential starters to optimize the fermentation processes and to obtain sauerkrauts with improved and standardized nutritional and sensory features. Furthermore, our correlations between microbiome composition and phenolics profile might also represent new references for sauerkraut biotechnology, aiming to identify new metabolic drivers of potential sauerkraut functionalities. Finally, sauerkraut ecosystem is a tractable model, although with high level of complexity, and resultant ecological information might be extended to other plant ecosystems
Starmerella bacillaris (synonym Candida zemplinina): evaluation of the impact against botrytis bunch rot on grape and the effect on winemaking
No full textVolatile organic compounds from Starmerella bacillaris to control gray mold on apples and modulate cider aroma profile
No full textGray mold caused by Botrytis cinerea is a fungal disease that can determine significant economic losses of apple during the storage phase. An alternative to reduce the use of traditional synthetic fungicides is to employ the yeast Starmerella bacillaris as biological control agent (BCA), also with positive effect on apple juice fermentation for the production of cider. Thus, we aimed to evaluate the safety of 16 S. bacillaris strains and their ability to control B. cinerea. In addition, the fermentation performances in apple juice and the volatile organic compounds (VOCs) profile were assessed, both in single-strain and in sequential fermentations with Saccharomyces cerevisiae. The in vitro assays showed that all S. bacillaris strains can be considered safe from the analyzed virulence factors, and were able to significantly constrain the growth of B. cinerea, reducing mycelial growth of 50% in dual-culture and of 90% through VOCs. Moreover, in vivo antagonistic assays revealed a visible decrease of gray mold rot symptoms on apples confirming the potential of S. bacillaris as BCA. GC-MS analysis of the ciders obtained showed increased concentrations in the sequential fermentation of some higher alcohols and terpenes, positively correlated with the cider aromatic quality, and suggested the involvement of benzyl alcohol, known for its antimicrobial action, in the biocontrol efficacy
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