The exogenous application of yeast-derived mannoproteins presents many opportunities for the improvement of wine technological and oenological properties. Their isolation from the cell wall of Saccharomycescerevisiae has been well studied. However, investigations into the efficiency of extraction methods from non-Saccharomyces yeasts are necessary to explore the heterogeneity in structure and composition that varies between yeast species, which may influence wine properties such as clarity and mouthfeel. In this study, nine yeast strains were screened for cell wall mannoprotein content using fluorescence microscopy techniques. Four species were subsequently exposed to a combination of mechanical and enzymatic extraction methods to optimize mannoprotein yield. Yeast cells subjected to 4 min of ultrasound treatment applied at 80% of the maximum possible amplitude with a 50% duty cycle, followed by an enzymatic treatment of 4000 U lyticase per g dry cells weight, showed the highest mannoprotein-rich yield from all species. Furthermore, preliminary evaluation of the obtained extracts revealed differences in carbohydrate/protein ratios between species and with increased enzyme incubation time. The results obtained in this study form an important step towards further characterization of extraction treatment impact and yeast species effect on the isolated mannoproteins, and their subsequent influence on wine properties.

One of the problems that most seriously affects oenology today is enzymatic browning, especially when grapes are infected by grey rot. We studied the capacity of glutathione (GSH) and a specific inactivated dry yeast rich in glutathione (IDY-GSH) to protect white grape must from browning compared to that of sulphur dioxide (SO₂). The results indicate that SO₂ drastically reduces the oxygen consumption rate (by around 72%), protects hydroxycinnamic acids from oxidation and prevents grape must against browning even in the presence of laccase. Specifically, the presence of SO₂ reduced the colour’s blue–yellow component (b*) by around 91% in control conditions and around 76% in the presence of laccase. GSH, pure or in the form of IDY-GSH, also reduces the oxygen consumption rate (by 23% and 36%, respectively) but to a lesser extent than SO₂. GSH also favours the formation of grape reaction product (GRP) from hydroxycinnamic acids and effectively protects grape must against browning in healthy grape conditions. Specifically, the presence of GSH reduced b* by around 81% in control conditions. Nevertheless, in the presence of laccase, it was not effective enough, reducing b* by around 39% in the case of pure GSH and 24% in the case of IDY-GSH. Therefore, both forms of GSH can be considered as interesting alternative tools to SO₂ for preventing browning in white grape must, but only when the grapes are healthy.

Due to the increase of the use of yeast derivatives (YDs) in winemaking to improve the technological and sensory properties in wines, in this work we evaluated the effect of the post-fermentation application of different yeast derivative products on the physical and chemical properties and astringency of red wines during two consecutive harvests. A commercial and two experimental new yeast derivatives were applied at a medium‒high dosage (30 g/hL). The addition of different yeast derivatives in red wine increased the concentration of different polysaccharide fractions and, therefore, the total polysaccharide content, producing a decrease in the duration of the wine astringency perception over time. The use of yeast derivatives could produce an adsorption/clarification and/or protective effect on the phenolic compounds. However, it did not produce an important modification of the colour parameters. An intensification or a lower decrease of the most volatile compound groups was produced, but it depended on the YDs and yeast strain used in fermentation and post-fermentation processes.

• Functionalisation of AFM dendritips with conA, WGA and anti-β-1,3/β-1, 6-glucan antibodies. • Cell wall polysaccharides were immobilized on epoxy-activated glass slides. • Specific binding of immobilized polysaccharides to functionalized dendritips. • Functionalized dendritips used as a new tool to probe yeast cell surface.

A thorough characterization of the polysaccharide part of Mannoprotein Pools (MPs) from nine different yeast strains was performed to assess biosynthesis-pathways impact on mannoproteins macromolecular structure and later establish structure-function relationships regarding stabilization properties. The strains comprised one wild-type S. cerevisiae strain, its mutants ΔMnn2 and ΔMnn4 (non-ramified N-glycosylated backbone and lacking mannosyl-phosphorylation, respectively), enological Saccharomyces cerevisiae strains grown in different metabolic conditions (aerobic and anaerobic), and three non-Saccharomyces species: Hanseniaspora vineae, Torulaspora delbrueckii, and Schizosaccharomyces japonicus. Neutral sugars composition for MPs of all strains had mainly mannose but Schizosaccharomyces japonicus strain also presented approximately 33 % of galactose. MPs from non-Saccharomyces strains exhibited significant differences in glycosyl-linkage analysis, especially those from Torulaspora delbrueckii and S. japonicus strains. Global net charge analysis of MP from S. japonicus strain suggests the presence of unknown negatively charged ions. These results dismiss the general N-glycosylated and O-Mannosylated structures obtained from S. cerevisiae. HPSEC-MALLS-QELS-Viscometry analysis revealed higher intrinsic viscosity profiles ([η]xMw) of H. vineae and S. japonicus MPs than S. cerevisiae ones. Metabolic conditions also influenced S. cerevisiae MPs biosynthesis: aerobiosis produced more negatively charged (20C.g^-1, net charge at pH 3.5) and less compact (ρ = 2.8) MPs than anaerobiosis (5C.g^-1 and 1.4).

Winemakers have to deal with enzymatic browning caused by a grape polyphenol oxidase called tyrosinase. Due to the problems related to sulphur dioxide and its use in winemaking, oenologists need alternative and effective treatments for inhibiting enzymatic browning. This research studies ascorbic acid, glutathione (pure and in the form of a specific inactivated dry yeast rich in glutathione), and bioprotection by a selected strain of Metschnikowia pulcherrima as alternatives to SO₂ for preventing enzymatic browning, following a methodology developed in previous works. All the studied treatments resulted in a significant reduction in enzymatic browning. More specifically, all treatments significantly reduced the Vmax of the apparent tyrosinase activity, indicating their potential to protect against enzymatic browning and thus allowing for a reduction in the doses of SO₂ added to the wine.