Yeasts walls

Lubbers, S., Charpentier, C., Eeulhat M., Voilley, A. (1994a). Influence of yeast walls on the behaviour of aroma compounds in a model wine. Am. J. Enol. Vitic., 45, 29-33,... 

Several treatment agents of wine yeast cell walls, sodium caseinate, gelatin, bentonite were evaluated for their potential to bind with aroma compounds. The loss of sensory properties of wine, especially flavor modification, is partly caused by protein stabilization treatments with fining agents or ultrafiltration processing of wine (IS 14). Yeast cell walls are used in sluggish or stuck wine fermentation the effect on fermentation has been explained by the adsorption of toxic fatty acids present in the growth medium (15). Therefore yeast walls are also assumed to bind aroma compounds. 

Yeast Cell Walls. Interactions between aroma substances and yeast walls induce to a modification of the volatility of some aroma compounds in the model wine (76/Yeast walls do not bind a specific chemical class of volatile compounds (Table II). The volatility of octanal, an aldehyde and of ethyl hexanoate, an ester, decreases by 14% with yeast walls at 1 g/L. The effect of walls is greater on the volatility of ethyl octanoate than that of the other aroma compounds the partition coefficient decreases by 45% for ethyl octanoate in the presence of 1 g/L yeast cell walls. 

The hydrophobic nature of the volatile substance seemed an important factor. The volatile compound with the highest hydrophobic constant (log P = 3.88), ethyl octanoate, is bound to a larger extent on yeast walls. Conversely, isoamyl alcohol, with log P= 1.21, is less fixed the decrease in volatility is 9%. 

Yeast cell walls are present in white wines which were aged on lees. Therefore we can suggest that yeast walls fi om lees influence on the equilibrium of the bouquet of the wine. 

Fining Agents. The binding capacity of caseinate, used for fining white and red wines was measured by heaspace analysis (Table III). Sodium caseinate at 1 g/L in model wine decreases the volatility of p-ionone more than that of ethyl hexanoate and isoamyl acetate. Like yeast walls, the most hydrophobic compound is the most bound to a larger extent. 

Figure 2. Percentage of binding with yeast cell walls and lipid-free yeast walls at 1 g/L and 10 g/L in the model wine by the equilibrium dialysis method.

The physico-chemical interactions between aroma compounds and other components depend on the nature of volatile compounds. The level of binding generally increased with the hydrophobic nature of the aroma. However interactions also depend on the nature of macromolecules such as yeast walls, mannoproteins, bentonite or smaller molecule such as ethanol. As a function of the nature of non-volatile component, the increase or decrease in the volatility of aroma compounds can influence largely the overall aroma of wine. 

This paper presents two models of enzymatic lysis of yeast cells a simplified two-step model, accounting for protein release at cell lysis followed by proteolysis, and a more complex mechanistic model which describes the removal of the two layers of the yeast wall and the extrusion and rupture of the protoplast and organelles. 

Figure 1 Double-layered structure of the yeast wall, enclosing the cell membrane...

Figure 8 shows a simulation of enzyme recovery from the wall, cytosol and mitochondria. The concentrations of recoverable enzyme are normalized to the initial amount of enzyme present in the cell site. The curves rise as enzyme is released from a site, then fall as it is hydrolyzed. It may be seen that the lytic system is usable even as a crude preparation to recover wall linked yeast enzymes in 60 to 80% yield. The yield of yeast wall enzyme depends on... 

The mannoproteins in question are more highly glycosylated, with an average molecular weight of approximately 40 kDa. They have been purified (Moine-Ledoux et al., 1997) from the same mannoprotein preparations, obtained by the enzymic treatment of yeast walls. 

An industrial preparation (Mannostab ) has been purified from yeast-wall mannoprotein. It is a perfectly soluble, odorless, flavorless, white powder. This product has been qnite effective (Table 1.20) in preventing tartrate precipitation in... 

It is quite true, however, that the lees gradually lose their capacity to reduce sulfur derivatives. This is probably due to the inactivation of the enzyme responsible for reducing sulfites to H2S (sulfite reductase). It is then possible for methanethiol and ethanethiol to fix on fresh yeasts, with even more serious consequences (Lavigne and Dubourdieu, 1996). Disulfide cross-bonds are formed between cysteine from the yeast wall mannoproteins and the SH group of the sulfur derivatives (Figure 8.21). The copper adsorbed by the yeast lees is involved to a large extent in the formation of disulfide cross-bonds between the free thiols and the cysteine remains of the... 

Trade Name Synonyms Deproteinated Yeasts t[Sederma http //www.sederma.fr]. Yeast Walls [Sederma http //www.sederma.fr]... 

Hydrocell AYP-30 Hydrocell YP-30 Hydrocell YP-30-P Hydrocell YP-SD Hydrolyzed yeast Hydrolyzed yeast protein Yeast Walls 100843-69-4 Pentavitin ... 

Hydrogenated vegetable glycerides 309-709-2 Hydrocell AYP-30 Hydrocell YP-30 Hydrocell YP-30-P Hydrocell YP-SD Hydrolyzed yeast Hydrolyzed yeast protein Yeast Walls 309-928-3 Ferro BP-10 Ferro BP-91 Ferro CP-18 Ferro CP-50 Ferro CP-68 Ferro CP-78 Ferro DP-25 Ferro EP-37... 

It is clear that the three-dimensional structure of the yeast wall is highly complex and not likely to exist as a bilayer of inner glucan and outer mannan as earlier proposed [44]. 

Fio. 1. Structure of the yeast wall jS (1 - 3) glucan. n -f n + n represent about sixty glucose... 

The initial studies carried out on the biosynthesis of yeast wall were directed towards learning the mechanisms of sugar polymerization in vivo, Bretthauer et fed Han-senula holstii cells with radioactive glucose or mannose and found that the extracellular mannan was produced from either sugar. 

P. Orlean, Biogenesis of Yeast Wall and Surface Components, in The Molecular and Cellular Biology of the Yeast Saccharomyees. Cell Cycle and Cell Biology, Volume 3, edited by J.R. 

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