Yeasts inhibition

Selected High-, Medium-, and Low-Severity Yeast Inhibition/ Enzymatic Hydrolysis Experiments on Aspen Wood and Corn Stover... 

Terrell, R.R.,J.R. Morris, M.G. Johnson, E.E. Gbur, andDJ. Makus. 1993. Yeast inhibition in grape juice containing sulfur dioxide, sorbic acid and dimethyldi-carbonate./. Food Sci. 58(5) 1132-1135. 

Cocolin, L. and D.A. Mills. 2003. Wine yeast inhibition by sulfur dioxide a comparison of culture-dependent and independent methods. Am.J. Enol. Vitic. 54 125-130. 

Table 4. Genus Names of Molds, Yeasts, and Bacteria Inhibited by Sorbates ...

Seafood. Sorbates are used to extend the shelf life of many seafood products, both fresh and processed (103,104). For smoked or dried fish, an instantaneous dip in 5 wt % potassium sorbate or a 10-minute dip in 1.0 wt % potassium sorbate prior to drying or smoking inhibits the development of yeast and mold (105,106). For fresh fish, sorbates can be incorporated at approximately 0.5 wt % into the ice, refrigerated seawater, or ice-water slush in... 

The effect of osmotic pressure on yeast activity is of great importance, and is often overlooked. At salt concentrations up to 1.5%, the effect is slight salt concentrations of 2—2.5%, which are common in bread doughs, inhibit yeast activity considerably. Likewise, sugar concentrations above 4% produce apparent inhibition. Consequently, yeast-raised sweet doughs (15—20% sugar), contain very high yeast concentrations. 

Clotrimazole and other azole derivatives have a different mode of action than the polyenes, eg, amphotericin B. The latter biad to the ergosterol present ia the membranes of yeasts and fungi, but azole derivatives inhibit the cytochrome P-450 dependent biosynthesis of ergosterol (8—11). This inhibition not only results in a reduction of ergosterol, but also in an accumulation of C-14 methyl sterols. They disturb membrane permeabiUty, inhibit cell rephcation, and are basically responsible, in combination with the reduction of ergosterol levels, for the antifungal action. 

Miconazole. Miconazole nitrate [22832-87-7] (Fig. 2), the 1-phenethyl-imidazole derivative first described in 1969, interferes at low doses with the cytochrome P-450 dependent ergosterol biosynthesis in yeasts and fungi. The result is accumulation of C-14 methylated sterols on the one hand and reduction of the ergosterol levels in the membranes on the other hand (12). Analogous to clotrimazole, this leads to a disturbance in the membranes it results in inhibition of ceU repHcation, mycelium development (in C. albicans) and finally, ceU death. High concentrations of miconazole, which may be achieved with topical use, disturb the orientation of phosphoHpids in the membranes, which produces leaks (13). 

Like the a2ole derivatives, it inhibits the biosynthesis of ergosterol. However, naftifine [65472-88-0] does not inhibit the cytochrome P-450 dependent C-14-demethylase, but the epoxidation of squalene. Squalene epoxidase cataly2es the first step in the conversion of squalene via lanosterol to ergosterol in yeasts and fungi or to cholesterol in mammalian cells. The squalene epoxidase in C. albicans is 150 times more sensitive to naftifine, C2 H2 N, than the en2yme in rat fiver (15). Naftifine is available as a 1% cream. 

The converted mash is pumped to a clean sterilised fermentor and the yeast inoculum is added. The set temperature range for whiskey fermentation of 72 hours is usually 17—21°C. At the beginning, the mash converted composition is approximately 80% sugars, mainly maltose and some (<1%) dextrose (primary conversion). The pH is adjusted to reduce initial bacterial growth. Grain neutral spidts are usually set at 27—29°C to expedite fermentation. Temperatures above 35°C inhibit yeast reproduction and promote rapid bacterial growth. Above 40°C actual yeast kill occurs. 

Sodium or potassium benzoate at a concentration of 0.05% is a universally used preservative agent active against yeast and mold. At higher concentrations benzoate is also effective against bacteria. It is most effective at a pH between 2.0 and 4.0. Sodium or potassium sorbate inhibits the growth of yeast and mold and is most effective below pH 6.5. 

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