Studies on Yeast Esterase

Abstract

An esterase (carboxylic acid hydrolase EC 3 1.1.1.) has been prepared from Saccharomyces cerevisiae. This esterase is active at pH 4 4 and, though it is unstable in solution, it can be main tained in an active form either by lyophilization or by coupling to an affinity gel. At pH 4 4, yeast esterase can hydrolyse between 20 and 40% of the esters commonly present in beer, and it is capable of synthesizing ethyl acetate from ethanol and acetic acid in a simple buffered solution without the provision of a co-factor. Different yeast strains yield different amounts of esterase, and there appears to be a positive correlation between the ability of the yeast to form esterase and the level of esters present in fermentations accomplished by that yeast.

Expression Levels of the Yeast Alcohol Acetyltransferase GenesATF1,Lg-ATF1, andATF2Control the Formation of a Broad Range of Volatile Esters

“…As esterases are responsible for the breakdown of esters, it is clear that their activity may affect the concentration of certain volatile esters. In S. cerevisiae, for example, it has been shown that the balance between ester-synthesizing enzymes and esterases, such as Iah1p (also known as Est2p), is important for the net rate of ester accumulation (27)(28)(29)(30) (59,60,61,62,70). This indicates that esterases may also play a role in the formation of certain esters (42,62,70).…”

“…In S. cerevisiae, for example, it has been shown that the balance between ester-synthesizing enzymes and esterases, such as Iah1p (also known as Est2p), is important for the net rate of ester accumulation (27)(28)(29)(30) (59,60,61,62,70). This indicates that esterases may also play a role in the formation of certain esters (42,62,70). In Acetobacter pasteurianus, for example, deletion of the esterase-encoding gene est1 causes the abolishment of ethyl acetate and isoamyl acetate production (15,36,37,50).…”

“…However, the effect of Iah1p on other esters, such as the group of ethyl esters, has not yet been thoroughly studied. In addition, partial purification of esterase activities in S. cerevisiae has shown that at least two different fractions with esterase activity exists, indicating that the proteome may contain more, as-yet-unidentified esterases (28,33,59,60,70,73,82). Hence, a possible role for these additional esterases in ester synthesis in brewer's yeast cannot be ruled out.…”

Solubilization and Activity Detection in Polyacrylamide Gels of a Membrane-Bound Esterase from an Oenological Strain of Saccharomyces cerevisiae

“…Their sensory threshold is very low, and thus they have a strong influence on the aroma of alcoholic beverages, giving characteristic flavours to, for example, wine 25 , beer 23 and sake 7 . Therefore, the study of enzyme activities, affecting the ester content and spectrum, is of primary importance in elucidating the mechanisms leading to the formation of the aroma profile of a fermented beverage such as wine.…”

“…Esterases are expressed in yeast strains used for alcoholic beverage production and their involvement in affecting the aroma of such beverages has been the subject of several studies. By regulating the equilibrium between esters and free acids, esterases might determine ester synthesis 3,12,20,23,25 , but seem to be mainly involved in their breakdown 6,8,12 . For example, isoamyl acetate, which is thought to be synthesized from isoamyl alcohol and acetyl CoA by yeast alcohol acetyltransferase, is hydrolyzed by yeast esterases in sake mash 7,8 thus affecting the flavour quality of this beverage.…”