331 research outputs found
Mannoproteins extracts from wine lees: characterisation and impact on wine properties
No full textThis study aims at exploiting an undervalued winemaking by-product, wine yeast lees, by developing efficient and food-grade methods for the extraction of yeast glycoproteins. These extracts were then supplemented to wine and their impact on wine properties assessed. White wine lees were produced by fermenting Sauvignon blanc grape juice with S. cerevisiae Uvaferm HPS strain. Three extraction methods were applied on lees using physical (autoclave and sonication) or enzymatic (Glucanex®, an industrial β-glucanases) approaches. Glycoproteins extracts were characterized by SEC-HPLC and SDS-PAGE. After their addition to wine (0.5 g/L), no alteration of wine clarity was detected. The ultrasonication and enzymatic extracts, containing a relatively low amount of glycoproteins, led to a significant decrease in wine protein haze formation upon heat test (-7%). Conversely, the autoclave extract was the richest in glycoproteins and had a positive impact on wine foaming properties, inducing an increase in foam’s maximum height and stability which were 2.6 and 3.6 times higher compared to a model wine. The autoclave extract improved tartrate stability as shown by a decrease in wine conductance (-11%) compared to the untreated wine. Results suggest that white wine lees could be considered a valuable source of glycosylated proteins with potential applications in winemaking. In this context, the autoclave appears as the more promising method in terms of both efficiency and extract’s effectiveness. The proposed food-grade exploitation approach could represent an important tool to improve the environmental and economical sustainability of the wine supply chain
Early fermentation volatile metabolite profile of non-Saccharomyces yeasts in red and white grape must: a targeted approach
No full textSaccharomyces cerevisiae is the main driver of alcoholic fermentation. It is typically inoculated at high levels to ensure successful implantation as well as reduce the risks of stuck fermentations and off-flavor production. However, winemakers have found that wines produced with only S. cerevisiae can be lacking in complexity compared to fermentations where non-Saccharomyces yeasts are more active. This study sought to understand the early fermentation characteristics of Kazachstania gamospora, Lachancea thermotolerans, Metschnikowia pulcherrima, Torulaspora delbrueckii and Zygosaccharomyces kombuchaensis in both Sauvignon blanc and Syrah musts. S. cerevisiae was used as a control. Solid-phase microextraction coupled to GC–MS was used to evaluate the musts once they reached 2% ethanol concentration. The method targeted 90 different compounds known to occur in wine and/or be produced by yeast during fermentation. For the first time, K. gamospora and Z. kombuchaensis have been studied in the context of wine. While the other yeasts are commercially available starter cultures, they have never been profiled this extensively. Analysis showed that each yeast profile was unique and different based on the must. The non-Saccharomyces yeasts produced lower concentrations of esters, alcohols and terpenes with the exception of K. gamospora which produced more total esters than the control
Controlling Stimulated Brillouin Backscatter with Beam Smoothing in Weakly Damped Systems
No full textUnravelling SO2 stress response in Brettanomyces/Dekkera bruxellensis using RNA-seq
No full textWine spoilage by Brettanomyces/Dekkera bruxellensis has increased in frequency because of the use of less-severe processing conditions, the great variety of diverse vinification tecniques and the tendency to reduce the use of preservatives, such as sulphur dioxide. Due to its antioxidant and antimicrobial effect, SO2 is a very common additive in many foods; however, it is also known for increased allergic reactions in humans and therefore consumer pressure to reduce the levels. The capability of B./D. bruxellensis to survive and to grow in wine can be partially ascribed to its high resistance to SO2, but no data are available on mechanisms involved in this metabolic trait.Triplicate batch fermentations were conducted in a wine-like medium using D. bruxellensis AWRI1499. Cells in exponential phase of growth were exposed to a molecular SO2 concentration of 0.35 mg/L and samples were collected for RNA-Seq analysis: i) before the SO2 pulse; ii) 5h thereafter; and iii) at cell growth recovery. Of the 4861 genes submitted to the gene set enrichment analysis (GSEA), 720 gene sets resulted upregulated. In particular, two distinct groups of gene sets resulted significantly enriched (p<0.01) in conditions ii) and iii), respectively. This result indicates that an early- and late response can be actuated by the yeast as a sequential strategy occurring under SO2 stress. Interestingly, SSU1, the main mechanism of sulphite detoxification in Saccharomyces cerevisiae, increased its expression during the late response up to 50 times. On the other hand, the data show that a long-term response, involving the carbohydrate biosynthesis and the sulphur compound metabolism, is activated and maintained by the yeast to counteract SO2 exposure
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Breakdown of Hot-Spot model in determining convective amplification in large homogeneous systems
No full textConvective amplification in large homogeneous systems is studied, both analytically and numerically, in the case of a linear diffraction-free stochastic amplifier. Overall amplification does not result from successive amplifications in small scale high intensity hot-spots, but from a single amplification in a delocalized mode of the driver field spreading over the whole interaction length. For this model, the hot-spot approach is found to systematically underestimate the gain factor by more than 50%
Biochemical characterization and evaluation of the oenological attributes of Lachancea species
No full textThesis (MScAgric)--Stellenbosch University, 2017.ENGLISH SUMMARY: Previously thought to be the catalyst for spoilt wine, several non-Saccharomyces yeasts are now commercially available for winemaking. Increasing investigations into this group of microorganisms has emphasized their oenological potential in terms of their contribution to the organoleptic profile of the resulting wines. However, their sub-optimal fermentation performances, force their combined inoculation with the main wine yeast Saccharomyces cerevisiae. Among the non-Saccharomyces yeasts, Lachancea thermotolerans has been reported to bring about an overall improvement in wine acidity through the production of L-lactic acid and reduction of acetic acid as well as increased glycerol and 2-phenylethanol levels, which can impart a sweet taste and flowery aromas to wine, respectively. Its secretion of hydrolytic enzymes of oenological relevance has also been reported. Other species of the Lachancea genus (L. fermentati and L. lanzarotensis) have also been isolated from the fermentation environment, but have not received the same degree of focus as L. thermotolerans. The aim of this study was to investigate the oenological potential of these species, regarding their expression of oenologically relevant enzymes, their fermentation attributes and the expression and location of β-glucosidase during fermentation of synthetic and real grape must (Muscat d’Alexandrie).
All the Lachancea spp. illustrated β-glucosidase activity in initial plate screenings, while none exhibited protease or pectinase activities. L. thermotolerans and L. fermentati also displayed higher tolerance to ethanol and SO2 when exposed to varying concentrations of these inhibitory compounds. Higher fermentation performance was demonstrated by L. thermotolerans strains and L. fermentati, which performed much better in Muscat grape juice, and was the only Lachancea spp. to complete the fermentation in monoculture. During these fermentations, all three Lachancea spp. illustrated β-glucosidase activity, where the highest levels were expressed by a L. thermotolerans strain, Y940. Most of the enzyme activity originated from the cell walls of the yeasts, while lower levels were isolated in the intracellular region and none determined to be released into the medium. The mixed culture fermentations resulted in wine products with significantly different chemical compositions compared to the S. cerevisiae fermentation. L. thermotolerans and L. lanzarotensis mixed culture fermentations resulted in similar wines with increased production of common compounds including isoamyl alcohol, butanol and ethyl phenylacetate. L. fermentati seemingly produced wines dissimilar to the other Lachancea spp., producing levels of acetic acid perhaps flagging this species as a potential spoilage microorganism. This study provided novel information on relatively uninvestigated Lachancea spp., where their oenological potential was highlighted by the ability to express β-glucosidase enzymes during fermentations and producing wines significantly different from S.AFRIKAANS OPSOMMING: ‘n Aantal nie-Saccharomyces giste, voorheen aan gedink as die kataliste vir bederfde wyn, is nou kommersieël beskikbaar vir wynbereiding. In diepte ondersoeke na hierdie groep mikro-organisms het hul wynkundige potensiaal, in terme van hul bydra tot die organoleptiese profiel van die gevolglike wyn, beklemtoon. Alhoewel, hul sub-optimale fermentasie gedrag forseer hul gekombineerde inokulasie saam met die hoof wyn gis Saccharomyces cerevisiae. Onder die nie-Saccharomyces giste, word berig dat Lachancea thermotolerans ‘n algehele verbetering in wyn suurheid te weeg bring deur die produksie van L-melksuur en ‘n verlaging in asynsuur asook ‘n verhoging in gliserol en 2-fenieletanol vlakke, wat onderskeidelik ‘n soet smaak en blommerige aroma aan die wyn kan verleen. Die afskeiding van hidrolitiese ensieme van wynkundige belang is ook al berig. Ander spesies van die Lachancea genus (L. fermentati en L. lanzarotensis) is ook al uit fermentasie omgewings ge-isoleer, maar hul is nie so in deeglik soos L. thermotolerans bestudeer nie. Die doel van hierdie studie was om die wynkundige potensiaal van hierdie spesies te ondersoek, met betrekking tot die uitdrukking van wynkundige relevante ensieme, hul fermentasie eienskappe en die setel van β-glukosidase gedurende fermentasie in sintetiese en egte druiwe sap (Muscat d’Alexandrie).
Al die Lachancea spp. het β-glukosidase aktiwiteit getoon in die plaat siftings, maar het geen protease of pektinase aktiwiteit getoon nie. L. thermotolerans en L. fermentati het ‘n hoë toleransie vir etanol en SO2 vertoon in ‘n inhibiese sifting met verkillende konsentrasies van hierdie inhibitoriese komponente. L. thermotolerans rasse en L. fermentati het ook hoër fermentasie prestasie getoon; hierdie spesies was die enigste Lachancea spp. wat as monokulture die fermentasie voltooi het en goeie prestasie in Muscat druiwe sap getoon het. Gedurende hierdie fermentasies het al drie Lachancea spp. β-glukosidase aktiwiteit getoon, met die hoogste vlakke wat deur L. thermotolerans ras Y940 uitgedruk is. Meeste van die ensiem aktiwiteit het in die selwand voorgekom, terwyl laer vlakke uit die intrasellulêre area ge-isoleer is en geen ensiem aktiwiteit in die medium as uitgeskeide ensiem voorgekom het nie. Die gemengde kultuur fermentasies het gelei tot wynprodukte met beduidend anderse chemiese samestelling in vergelyking met S. cerevisiae fermentasie. L. thermotolerans en L. lanzarotensis gemengde kultuur fermentasies het soortgelyke wyne met hoër produksie van algemene verbindings, insluitend isoamiel alkohol, butanol, en etiel fenielasetaat, opgelewer. L. fermentati het oënskynlik wyne geproduseer wat heelwat anders is as die ander Lachancea spp., met vlakke van asynsuur wat moontlik ‘n aanduiding is dat die spesie ‘n potensiele bederf mikroorganisme is. Hierdie studie het nuwe inligting oor die relatief onbestudeerde Lachancea spp. getoon, waar hul wynkundige potensiaal uitgelig is deur die vermoë om β-glukosidase ensieme uit te druk gedurende fermentasies en om wyne te produseer wat beduidend anders is as die van S. cerevisiae.Master
Investigation of the SO2 stress response in Brettanomyces/Dekkera bruxellensis using RNA-seq
No full textSulphur dioxide (SO2) is the most common additive worldwide used to prevent and/or control the microbial contamination in wine. Its use should be limited due to the detrimental effect to human health and the intolerance shown by a number of wine consumers. Brettanomyces/Dekkera bruxellensis, the main spoilage yeast of wine, is able to growth and produce volatile phenols even when SO2 is present. The SO2 resistance is a strain-dependent characteristic that needs to be further investigated. The two completely sequenced strains of B./D. bruxellensis, AWRI1499 (Curtin et al., 2012) and CBS2499 (Piškur et al., 2012), were used for batch fermentations carried out in synthetic wine medium. When cells reached the exponential phase of growth, SO2 was added (0.35 mg/L as molecular SO2). Samples for transcriptomic analysis were collected before SO2 pulse (T0), 5 hours after the addition (T5h) and at cell growth recovery (Tr). The results showed that more genes were significantly differentially expressed within the comparison Tr-vs-T0 than in the T5h-vs-T0 in both strains, thus indicating that mainly an adaptive response is activated. Among genes affected by SO2 addition and shared by the two strains, upregulated genes participating to carbohydrate, acyl-CoA and monocarboxylic acid metabolism were found. Interestingly, AWRI1499-0080, the gene homolog to SSU1, encoding the enzyme involved in the main mechanism of sulphite detoxification in Saccharomyces cerevisiae, increased its expression in the long term response up to 4 and 47 folds in CBS2499 and AWRI1499, respectively, thus highlighting the importance of this detoxification mechanism in B./D. bruxellensis as well. This study confirms the great ability of B./D. bruxellensis yeasts to survive and growth in extreme environmental conditions. In conclusion, due to the capacity of this yeast to counteract the stress induced by the addition of SO2, a proper management of the winemaking, including a deep cleaning of the winery equipment, is advisable for preventing, or at least minimizing the Brett contamination in wine
Minimax spectral estimation of weighted Laplace operators
No full textGiven n i.i.d. observations, we study the problem of estimating the spectrum of weighted Laplace operators of the form ∆ f = ∆ + α∇ log f • ∇, where f is a positive probability density on a known compact d-dimensional manifold without boundary and α ∈ R is a hyperparameter. These operators arise as continuum limits of graph Laplacian matrices and provide valuable geometric information on the underlying data distribution. We establish the exact minimax rates of estimation for this problem, by exhibiting two different rates of convergence for eigenfunctions and eigenvalues. When f belongs to a Hölder-Zygmund class C s of regularity s 2, the eigenfunctions can be estimated with respect to the L q -norm (q 1) via plug-in methods at the minimax rate n -s+1 2s+d for d 3 (with different rates for d 2). Moreover, eigenvalues can be estimated at the minimax rate n -4s 4s+d + n -1 2 . In the regime s > d 4 , we further show that asymptotically efficient estimators exist.We also present a general framework for estimating nonlinear functionals over Hölder-Zygmund spaces, with potential applications to a broad class of statistical problems
Minimax spectral estimation of weighted Laplace operators
No full textGiven n i.i.d. observations, we study the problem of estimating the spectrum of weighted Laplace operators of the form ∆ f = ∆ + α∇ log f • ∇, where f is a positive probability density on a known compact d-dimensional manifold without boundary and α ∈ R is a hyperparameter. These operators arise as continuum limits of graph Laplacian matrices and provide valuable geometric information on the underlying data distribution. We establish the exact minimax rates of estimation for this problem, by exhibiting two different rates of convergence for eigenfunctions and eigenvalues. When f belongs to a Hölder-Zygmund class C s of regularity s 2, the eigenfunctions can be estimated with respect to the L q -norm (q 1) via plug-in methods at the minimax rate n -s+1 2s+d for d 3 (with different rates for d 2). Moreover, eigenvalues can be estimated at the minimax rate n -4s 4s+d + n -1 2 . In the regime s > d 4 , we further show that asymptotically efficient estimators exist.We also present a general framework for estimating nonlinear functionals over Hölder-Zygmund spaces, with potential applications to a broad class of statistical problems
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