Ethanol fatty acyl composition

The relationship between the fatty acid composition of the membrane lipids and an organism s ethanol tolerance also has been investigated using mutants of E. coli. The membrane fatty acyl composition of E. coli is easily manipulated using mutants... 

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). 

The complete transesterification of 1 mol of TAG requires 3 mol of alcohol, producing 1 mol of glycerol and 3 mol of fatty esters (Fig. 22.8). As the reaction is reversible, alcohol is commonly added in excess in industrial processes to ensure the direction of fatty acyl esters. A number of alcohols can be used as the substrates, eg, methanol, ethanol, propanol, butanol, and amyl alcohol. Methanol is the most preferable one because of its low cost. The most abundant composition of microalgal oil transesterified with methanol is C19H36O2, which has been demonstrated to meet the standard of biodiesel (Xu et al., 2006). 

High-molecular-weight esters, such as wax esters, steryl esters, triterpenoid esters and triacylglycerols, are often hydrolysed, after which the liberated moieties are GC analysed however, this procedure provides only limited compositional information. The very convenient one-pot small-scale hydrolysis-silylation procedure, applicable to ester-emulsifiers, oils, fats, wax esters and other hydrolysable lipids, has been proposed by the lUPAC (Briischweiler and Hautfeune, 1990). The procedure involves the saponification of esters (ca. 10 mg) in 0.5 N ethanolic KOH solution (0.25 mL) at 80 °C for 3 h, evaporation to dryness in a stream of nitrogen and then silylation of the hydrolysis products. This enables the components of very small samples to be determined (< 0.1 mg). This procedure was used for the hydrolysis of wax esters and triterpenoid esters in potato and eggplant cuticular waxes (Szafranek Synak, 2006 Halinski et al., 2009). A solution of 1-2% (v/v) concentrated sulphuric acid in methanol can be easily used for the transesterification of acyl lipids and the esterification of free fatty acids (Christie, 1994). More procedures for ester hydrolysis and transesterification and for fatty acid esterification are described in detail by Christie (1994). 

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