2-phenylethanol yeast

Phenylethanol L-Phenylalanine Diverse yeasts e.g. Saccharomyces and Kluyveromyces >10gL , 30 h, 0.5-1 tyear Fed-batch cultivation in situ product recovery by two-phase system with more than 25 g L in the organic phase possible [109,120]... 

Phenylethanol has a rose-like odour and makes the chemically produced compound the most used fragrance chemical in perfume and cosmetics, with a world market of about 7,000 t year [107, 108]. 2-Phenylethanol is also found in many foods as a characteristic flavour compound rounding off the overall aroma, especially in foods obtained by fermentation, such as wine, beer, cheese, tea leaves, cocoa, coffee, bread, cider and soy sauce [109]. In food applications, natural 2-phenylethanol is preferred rather than its nature-identical counterpart from chemical synthesis and it has a market volume of 0.5-11 year . This product is sold at market prices of up to US 1,000 per kiklogram and is mainly produced by yeast-based bioprocesses since its isolation from natural sources, e.g. rose oil, would be too costly [109]. 

Although 2-phenylethanol can be synthesised by normal microbial metabolism, the final concentrations in the culture broth of selected microorganisms generally remain very low [110, 111] therefore, de novo synthesis cannot be a strategy for an economically viable bioprocesses. Nevertheless, the microbial production of 2-phenylethanol can be greatly increased by adding the amino acid L-phenylalanine to the medium. The commonly accepted route from l-phenylalanine to 2-phenylethanol in yeasts is by transamination of the amino acid to phenylpyruvate, decarboxylation to phenylacetaldehyde and reduction to the alcohol, first described by Ehrlich [112] and named after him (Scheme 23.8). 

Extraction into capsules with a solvent, for example, recovery of phenylethanol (a product of phenylalanine bioconversion by yeast) [67] or lactic acid from fermentation broth [68], has attracted interest recently. The polymeric core of the capsule prevents direct contact of the solvent with biomass. This process could be regarded as a batch MBSE. 

In experiment 2, higher alcohols originating from amino acid metabolism, such as 2-methy1-1-propanol, 3-methyl-l-butanol and 2-phenylethanol were found as metabolization products of B cinerea. Figure 3 shows distinct quantitative differences depending on the strain used. Control experiments demonstrated that these alcohols were exclusively formed by B cinerea and not by contamination by yeasts. This fact should be stressed since contradictory results have been published (2,3). 

The main volatiles in wines are the higher aliphatic alcohols, ethyl esters, and acetates formed from yeasts during fermentation. Acetates are very important flavors characterized by fruity notes, C4-Ci0 fatty acid ethyl esters manly confer fruity scents to the wine. Other wine aroma compounds are C6 alcohols, such as 1-hexanol and cis- and trans-3-hexen-l-ol, 2-phenylethanol, and 2-phenylethyl acetate. Contents of these compounds in wine are linked to the winemaking processes used fermentation temperature, yeast strain type, nitrogen level in must available for yeasts during fermentation, clarification of wine (Rapp and Versini, 1991). Much literature on the wine aroma compounds was reported in reviews by Schreier (1979) and Rapp (1988). 

Pichiafurans A-C (98—100) and pichiacins A (101) and B (102) have been characterized from the yeast Pichia membranifaciens, which was obtained from the Korean marine sponge Petrosia sp. So far, no marine isolates of the genus Pichia had been described, and this yeast had not been studied with regard to its secondary metabolite chemistry. Compounds 98—100 are friryl ethers with 2-phenylethanol, while 101 and 102 are esters consisting of 2-phenylethanol and short-chain w-hydroxy acids. 

Other types of ketones can also be modified to improve the enantioselectivities, and various functionalities can be used to modify the substrate to produce the corresponding alcohol with higher enantioselectivities. For example, the reduction of acetophenone by yeast results in the formation of phenylethanol in 69 % ee, whereas the reduction of p-iodoacetophenone followed by the dehalogenation results in a product of 96% ee (Fig. 15-11) 165l... 

Cox et al. [7] report that styrene-degrading fungi can also be isolated quite readily, provided that the styrene concentration is kept low. One strain, isolated by van der Werf at pH 4.5 [18], was identified as a black yeast, Exophiala jeanselmei and studied in more detail. Based on the growth-substrate utilization pattern and oxygen-uptake experiments, Cox et al. [7] suggest that styrene oxide, 2-phenylethanol, and phenylacetate could be intermediates of the styrene degradative pathway in this eukaryote. 

Williamson s medium L Contains ui opped beer, maltose, yeast extract, liver extract, casein hydrolysate, either polymyxin or phenylethanol with CO atmosphere (25 Q, supports lactic acid bacteria. Polymyxin suppresses gram-negative bacteria. Phenylethanol supports Pediococcus rather than Lactobacillus... 

Ester formation is associated with yeast growth in the early phase of fermentation. Acetate esters are produced via the reaction between an alcohol and acetyl Co-A, which is catalysed by the enzyme alcohol acetyl transferases (ATFl and ATF2). Ethanol, branched-chain alcohols and 2-phenylethanol are the common moieties of acetate esters. Ethyl esters of medium-chain fatty adds are formed through the reaction between ethanol and respective fatty acyl Co-A, which is catalysed by the enzyme alcohol acyl transferases. Saccharomyces cerevisiae strains also produce esterases that hydrolyse esters, and thus the final concentration of esters in beers is the net balance between ester synthesis and hydrolysis. Strains of brewing yeasts produce predominantly ethyl esters of fatty acids, particularly ethyl octanoate, with relatively little formation of acetate esters. Ester production in beer is regulated by a number of factors such as yeast strain, temperature, hydrostatic pressure, wort composition, sugar type and concentration, type and amount of yeast-assimilable nitrogen, aeration, and unsaturated fatty acids (Hiralal, Olaniran, PiUay, 2014 Pires et al., 2014). 

Fusel oil formation varies with yeast strain, temperature of fermentation, pH, nutritional status, suspended solids level, and oxygen concentration of juice/must. Under oxidative conditions as would occur before the onset of alcoholic fermentation, or in cases of stuck fermentation, Pichia, Hansenula, and Candida may produce substantial quantities of fusel alcohols from fermentable sugars. The fusel alcohol, 2-phenylethanol (arising from 2-phenylalanine), has the unmistakable odor of roses and is also... 

Fig. 15.49. Time curves of the formation of 2-phenylethanol ( - ) and 3-methylbutanol (o-o) in a prefermented dough (according to Gassenmeier and Schieberle, 1995) flour (59 g), water (50 g) and yeast (0.25 g) were incubated at 30 °C...

The main aroma substances produced by yeast in breadcrumbs are aldehydes, alcohols, acetals and sulfur compounds. The most important components are 2-phenylethanol and 3-methylbutan-... 

Guymon etal., 1961). Yet production by wine yeasts is limited, even in spontaneous fermentation. More recently, various researchers have shown that most S. bayanus (ex uvarum) produce considerably more phenylethanol than S. cerevisiae. Finally, higher alcohol production in S. cerevisiae depends on the strain. A limited higher alcohol production (with the exception of phenylethanol) should be among selection criteria for wine yeasts. 

Phenylethanol production is very strain-specific [65] and has been rarely observed in bacteria (Brevibacterium linens. Microbacterium sp.), while it is much more common in fungi. The best producers are doubtlessly the yeasts Kluyveromyces marxianus [66, 67] and Saccharomyces cerevisiae [68], but lower yields have been obtained with many strains, such as K. lactis [69], Pichia fermentans [70, 71], and P. (formerly//a/ise/i /a) anomala [72]. 

Etschmaim, M.M.W., Sell, D., and Schrader, J. (2003) Screening of yeasts for the production of the aroma compound 2-phenylethanol in a molasses-based medium. Biotechnol Lett, 25, 531-536. 

An aqueous-organic two-phase bioprocess for efficient production of the natural aroma chemicals 2-phenylethanol and 2-phenylethylacetate with yeast. Appl Microbiol Biotechnol,... 

Wang, H., Dong, Q., Meng, C., Shi, X., and Guo, Y. (2011) A continuous and adsorptive bioprocess for efficient production of the natural aroma chemical 2-phenylethanol with yeast. Enzyme Microb. Technol, 48, 404-407. 

Inquiries into the possible production of behavioral chemicals of D. frontalis by microorganisms associated with it have been carried further. As mentioned above, two fungi and two yeasts are associated with the mycangium of the female (440, 441). The production of various volatile substances, other than ethanol, by actively fermenting yeasts is well established (445). Brand et al. (446) grew three yeasts obtained from D. frontalis, namely H. holstii, P. pinus, and P. bovis, on Sabouraud s dextrose broth, and identified isoamyl alcohol, 2-phenylethanol, isoamyl acetate and 2-phenylethyl acetate as the main volatile substances (other... 

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