Production and biological function of volatile esters in Saccharomyces cerevisiae

Abstract

SummaryThe need to understand and control ester synthesis is driven by the fact that esters play a key role in the sensorial quality of fermented alcoholic beverages like beer, wine and sake. As esters are synthesized in yeast via several complex metabolic pathways, there is a need to gain a clear understanding of ester metabolism and its regulation. The individual genes involved, their functions and regulatory mechanisms have to be identified. In alcoholic beverages, there are two important groups of esters: the acetate esters and the medium‐chain fatty acid (MCFA) ethyl esters. For acetate ester synthesis, the genes involved have already been cloned and characterized. Also the biochemical pathways and the regulation of acetate ester synthesis are well defined. With respect to the molecular basis of MCFA ethyl ester synthesis, however, significant progress has only recently been made. Next to the characterization of the biochemical pathways and regulation of ester synthesis, a new and more important question arises: what is the advantage for yeast to produce these esters? Several hypotheses have been proposed in the past, but none was satisfactorily. This paper reviews the current hypotheses of ester synthesis in yeast in relation to the complex regulation of the alcohol acetyl transferases and the different factors that allow ester formation to be controlled during fermentation.

Review of Aroma Formation through Metabolic Pathways of Saccharomyces cerevisiae in Beverage Fermentations

“…Ethyl esters include ethyl butanoate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate (Saerens et al 2010). These ethyl esters vary in their sensorial attributes, but descriptions include apple, fruit, strawberry, pear, and aniseed (Saerens et al 2010). During the late exponential growth phase, MCFA intermediates are released prematurely from the cytoplasmic fatty acid synthase (FAS) complex, and this release triggers ester synthesis (Taylor and Kirsop 1977).…”

“…Ethyl esters include ethyl butanoate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate (Saerens et al 2010). These ethyl esters vary in their sensorial attributes, but descriptions include apple, fruit, strawberry, pear, and aniseed (Saerens et al 2010).…”

“…Esters contribute to the floral and fruity characteristics associated with wines and beer and are generated by the esterification of alcohol and acids at low pH (Saerens et al 2010). The reaction requires an alcohol molecule, acetyl-CoA, an ester-synthesizing enzyme, and adenosine triphosphate (ATP; Figure 2B and 2C) (Saerens et al 2010).…”

“…Acetate esters result from the esterification of acetyl-CoA and an alcohol ( Figure 2B). These acetates include ethyl acetate, isoamyl acetate, 2-methylbutyl acetate, and phenylethyl acetate, and are described as having banana, apple, fruit, and aromatic sweetness, respectively (Saerens et al 2010). Ethyl acetate is the most common acetate ester in fermentations, primarily because of the large quantities of ethanol in these metabolic processes and the more reactive nature of primary alcohols (Saerens et al 2010).…”

“…The second group, the ethyl esters, is composed of ethanol and a medium-chain fatty acid (MCFA) ( Figure 2C) (Saerens et al 2010). Ethyl esters include ethyl butanoate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate (Saerens et al 2010).…”