Development of a genetically defined diploid yeast strain for the application in spirit production [Elektronische Ressource] / von Beatus Schehl

Informations

• Publié par: universitat_hohenheim
• Publié le: 01 janvier 2005
• Nombre de lectures: 31
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Institut für Lebensmitteltechnologie
Universität Hohenheim
Fachgebiet: Gärungstechnologie Prof. Dr. J. J. Heinisch






Development of a genetically defined
diploid yeast strain for the application in
spirit production





Dissertation
zur Erlangung des Grades eines Doktors
der Naturwissenschaften


der Fakultät Naturwissenschaften
der Universität Hohenheim


von
Beatus Schehl
aus Landau in der Pfalz

2005





















Die vorliegende Arbeit wurde am 28.10.2003 von der Fakultät
Naturwissenschaften der Universität Hohenheim als „Dissertation zur Erlangung
des Grades eines Doktors der Naturwissenschaften“ angenommen.




Tag der mündlichen Prüfung: 21.10.2005

Dekan: Prof. Dr. H. Breer
Berichterstatter, 1. Prüfer: Prof. Dr. J. Heinisch
Mitberichterstatter, 2. Prüfer: PD Dr. T. Senn
3. Prüfer: Dr. V.Kottke
















„Dosis facit venenum“
Paracelsus, 1493 - 1541




CONTENTS


Chapter I Scope and outline 1

Chapter II General Introduction 6

Chapter III A laboratory strain suitable for spirit production 41

Chapter IV Effect of the stone content on the quality of plum
and cherry spirits produced from mash fermenta-
tions with commercial and laboratory yeast strains 72

Chapter V Reduction of ethyl carbamate in stone fruit spirits
by manipulation of the fermenting yeast strain 96

Chapter VI Retrospective trends and current status of ethyl
carbamate in German stone fruit spirits 106

Chapter VII Concluding remarks 128
VIII Zusammenfassung 139

Appendix Lebenslauf

Erklärung
Chapter I


CHAPTER I

SCOPE AND OUTLINE OF THE Ph.D. THESIS


Scope
The diversity and the composition of the yeast micropopulation during fruit fermentations
contributes significantly to the sensory characteristics of the spirits. The growth of each yeast
species is characterized by specific metabolic activities, which determine concentrations of
flavour compounds in the final product (Walker, 1998). However, it should be pointed out
that, within each yeast species, significant strain variability has been recorded (Younis and
Steward, 1998). The wide use of starter cultures of Saccharomyces cerevisiae, mainly
applied to reduce the risk of spoilage and unpredictable changes of flavour, ensures a
balanced quality. On the other hand it may also cause a loss of characteristic aroma and
flavour determinants.

Therefore it could be of great benefit to select and combine certain characteristics of different
yeast strains. These could be adjusted according to need not only in spirit production, but
also in wine and beer making, to optimize and ensure a reproducible quality. Currently there
is a large number of different yeast strains for spirit and wine production on the market.
These have been isolated, selected and cultivated from spontaneous fermentations, are
readily available and are all claimed to have perfect fermentation skills. In general, little
genetic research has been devoted to yeast strains used in fermentation and baking
industries. If any, this has concentrated on the winery busyness (Pretorius, 2000). Since
financial resources are very scarce for scientific investigations in spirit productions, little
attention has been paid to biological improvements.

Accordingly, the yeast strains commonly employed for alcohol production are genetically
largely undefined and highly heterogeneous (Benitez et al., 1996). Thus, little is known about
their chromosomal constitution and aneuploidy is frequently observed (Bidenne et al., 1992,
Cardinali and Martini, 1994, Vezinhet, 1981). This prevents the use of standard genetic
manipulations such as crossings and tetrad analysis for strain improvement. Furthermore, it
complicates the application of the majority of modern methods developed in yeast molecular
biology (Pretorius, 2000). The application of laboratory yeast strains for industrial purposes
offers the potential of a genetic and physiological design, since the complete genome
1 Chapter I


sequence of S. cerevisiae is available (Goffeau et al., 1996; Zagulski et al., 1998). Recently,
laboratory strains have been developed with improved metabolic features (van Dijken et al.,
2000). The efficiency of fermentation could further be improved e. g. by a better sugar
utilization, an increased ethanol tolerance, resistance to zymocins and heavy metals,
reduced formation of foam, induced flocculance at the end of fermentation, the production of
extracellular (or liberated) enzymes or the reduced formation of undesired metabolites. For
example, ethyl carbamate (EC) which is mainly found in fermented foods and beverages, has
been listed as a carcinogenic agent. Especially in stone fruit brandies EC can additionally
origin from the fruit itself. EC forms in fermented food by the reaction of urea and ethanol
(Ough et al., 1988a, Pretorius, 2000). It has been assumed that yeast contributes substan-
tially to EC formation since urea is formed during arginine degradation (Ough et al., 1988b,
Kitamoto et al., 1991).

Regarding the performance in alcoholic fermentation, it has been claimed that laboratory
strains show worse ethanol production kinetics. Furthermore, it is generally believed, that
such strains lead to the appearance of undesired aromatic compounds in fermented fruit.
Based on the prospect of strain improvement in this work, a genetically well defined
prototrophic diploid laboratory yeast strain should be constructed and tested for its
fermentative and sensory performances in spirit production. Such a strain offers the potential
for further genetic modification by classical breeding and modern molecular genetic
techniques, to adjust yeast physiology to special production schemes.


Outline
Chapter II provides an introduction to (i) the fundamentals of the distillation process, (ii) yeast
metabolism with regard to the degradation of carbohydrates and nitrogen compounds as well
as the formation of secondary fermentation products and flavours, and (iii) the relevance of
ethyl carbamate in spirits with a special focus on its origins.

Chapter III describes the construction of a laboratory yeast strain and its suitability for
fermentation of fruit mashes in spirit production. The fermentation skills of the laboratory
strain are compared to industrial yeast strains. Finally, the influence of the different yeast
strains employed on the sensory quality of the spirits has been determined. An outline for
future applied research is given, involving genetic possibilities for improvements in spirit
2 Chapter I


production. This chapter has been published in: Schehl, B., C. Müller, T. Senn, and J. J.
Heinisch: A laboratory strain suitable for spirit production. Yeast 21:1375-89, 2004.

Chapter IV comprises experiments evaluating the influence of the stone content on the
quality and flavour of plum and cherry spirits combined with analytical assessments of the
spirits using the laboratory strain and some industrial yeast strains. This chapter has been
published in: Schehl B., T. Senn, and J. J. Heinisch. Effect of the stone content on the quality
of plum and cherry spirits produced from mash fermentations with commercial and laboratory
yeast strains. J. Agric. Food Chem. 53:8230-38, 2005.

Chapter V describes the characteristics of spirit production using the established laboratory
strain HHD1 compared with its genetically modified mutant HHD1delCAR1 in laboratory
scale experiments. Furthermore the dependence of the EC content on the yeast strain
employed has been investigated. Finally, the data are related to the technological procedure
used for spirit production. This chapter has been submitted for publication: Schehl, B., D.
Lachenmeier, T. Senn, and J. J. Heinisch: Reduction of ethyl carbamate in stone fruit spirits
by manipulation of the fermenting yeast strain. Appl. Environ. Microbiol., submitted.

In chapter VI a statistical analysis of a database with regard to ethyl carbamate in stone fruit
spirits in the Southern part of Germany over the last 15 years is reported. A discussion on
acceptable methods of spirit production based on “state of the art technology” is supported
by these data. This chapter has been published in: Lachenmeier, D. W., B. Schehl, T.
Kuballa, W. Frank, and T. Senn: Retrospective trends and current status of ethyl carbamate
in German stone-fruit spirits. Food Additives and Contaminants 22:397-405, 2005.


CONTRIBUTIONS OF CO-AUTHORS

The co-authors Prof. Dr. Jürgen J. Heinisch and Priv. Doz. Dr. Thomas Senn (Chapters 3
to 5) contributed by their supervision, financial support