LIPID METABOLISM AND THE REGULATION OF VOLATILE ESTER SYNTHESIS INSACCHAROMYCES CEREVISIAE

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Abstract
The specific rates at which ethyl acetate and iso-amyl acetate are produced by yeast increase markedly at that point in fermentation where syntheses of lipids (i.e. saturated fatty acids and squalene) stop. An increase in the acetyl-CoA: CoASH ratio, or a reduced availability of substrates (fatty acyl-CoAs) for acyl transferases, are possible reasons for such a stimulation of ester synthesis. Increased rates of ester production are not sustained but contribute significantly (ca. 30% for ethyl acetate) to the total concentration of acetate esters in beer fermented from 1·040 all-malt wort. Addition of linoleic acid (50 mg litre−1) suppresses the induction of ester synthesis and reduces overall formation of both ethyl and iso-amyl acetates by ca. 80%. Possibly, linoleic acid exerts these effects either by directly inhibiting the activity of an ester-synthesising enzyme, or by allowing alternative use of acetyl-CoA for the synthesis of saturated fatty acids.