P-6
A three-member genes family is responsible for the synthesis of short chain
fatty acid esters during fermentation. Ester synthesis during fermentation mainly depends on yeast ester synthesis
potential, i.e. the amount of available acetyl-CoA/acyl-CoA (an essential
building block for yeast cellular components) and the level of ester synthase
activities, the enzymes being synthesised during the growth phase. Biochemical
evidence suggests that at least five enzymes are involved in the synthesis of
esters within yeast. Ester hydrolyzing activities may play a determinant role on
the final beer ester levels of products such as membrane filtered beer and
bottle re-fermented beer. Recently, scientists have taken advantage of the
completed S. cerevisiae genome sequence database and the powerful tools
of molecular biology to identify the corresponding genes and investigate the
physiological role of ester synthesis. Recent rapid progress has provided
insights not only into the regulation of cellular ester synthesis, but also into
some general mechanisms of gene regulation. Three distinct AATase genes (ATF1,
LgATF1 and ATF2), responsible for the production of acetate esters, have been
cloned from different yeast backgrounds. A fourth gene, EHT1, has been described
as an ethanol hexanoyl-CoA transferase. In this work, we report the effect of
EHT1 disruption on the synthesis of esters. Sequence comparisons revealed that
EHT1 belongs to a three-member gene family. Combination of simple, double and
triple deletions did not affect growth. Disruption of one of the genes resulted
in decreased levels of short chain acid esters, the decrease being accentuated
with the number of disrupted genes. The results suggested an internal functional
redundancy as the phenotype was increased with the number of disrupted genes.
Analysis of the relationship between levels of short chain fatty acids and the
corresponding ethyl esters strongly suggests that these enzymes may be involved
in the removal of the toxic short chain fatty acids. Interestingly, disruption
of the three-member genes family also stimulated the synthesis of the acetate
esters.
Jean-Pierre Dufour. Studies: MSc., 1975-PhD., 1979 (Louvain). Research
fellow (Johns Hopkins University, School of Medicine, Baltimore, MD) 1979-1981.
Appointments: Catholic University of Louvain, Professor 1981-1993 (Head of the
Department of Brewery and Food Industries, 1987-1993); Universidade Catolica
Portuguesa, Escola superior de Biotechnologia (Porto, Portugal), visiting
Professor 1989-1994; University Senghor (Alexandria, Egypt), associated
Professor 1992-1995; Expert for EEC and UNIDO (Implementation of sorghum malt
for the production of lager beer in Africa) (1994-1996); University of Otago,
Dunedin, New Zealand, Professor (1995-present), Chairperson and Head of
Department of Food Science. Expertise: Flavour science, fermentation science and
technology, malting and brewing sciences, yeast biochemistry/enzymology. Active
member of EBC Brewing Science Group, ASBC, IOB, Institute of Food Technology,
American Chemical Society, New Zealand Institute of Food Science and Technology.
Vice-president and Fellow of the New Zealand Institute of Food Science and
Technology, New Zealand delegate to IUFoST.
JEAN-PIERRE DUFOUR (1), B. Llorente (2), B. Dujon (2), S. Kumara (1), K.
Verstrepen (3) and G. Derdelinckx (3). (1) Dept Food Sci, Univ Otago, POB 56,
Dunedin New Zealand; (2) Unité Génét Moléc Levures, Dept Biotech, 25 rue du Dr
Roux, 75724, Paris France; (3) Centre Malt & Brew Sci, Dept Food & Microbial, KU
Leuven, Kardinaal Mercierlaan 92, 3001 Heverlee, Belgium.