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Contents
INTRODUCTION................................................................................................................................ 4
PART I - GENERAL ASPECTS REGARDING THE SCIENTIFIC ADVANCES IN THE BIOLOGY AND
TECHNOLOGY OF YEASTS .......................................................................................................... 7
1. Characterization and classification of yeasts ................................................................................. 7
1.1 .Taxonomic and technological characters of beer yeasts ..................................................11
1.2. Taxonomic and technological characteristics of wine yeasts ..........................................19
2. The morphology and anatomy of yeasts ...................................................................................... 23
2.1. Cultural characteristics of yeasts ...................................................................................23
2.2. Morphological characters of yeasts ...............................................................................23
2.2.1. The sizes of yeasts ..................................................................................................... 23
2.2.2. The shapes of yeasts .................................................................................................. 24
2.2.3. The cellular structure of yeasts .................................................................................. 25
3. The reproduction and life cycle of yeasts .................................................................................. 38
4. The biochemistry and physiology of yeasts ............................................................................... 47
4.1. The chemical composition of yeasts .............................................................................47
4.2. The nutrition of yeasts ..................................................................................................64
4.2.1. The relation between fermentation and respiration (Pasteur effect and
Crabtree effect).................................................................................................................... 65
4.2.2. The nutritional and development necessities ............................................................. 67
4.2.2.1. Carbon sources ........................................................................................... 67
4.2.2.2. Nitrogen sources......................................................................................... 74
4.2.2.3. Phosphor sources ........................................................................................ 78
4.2.2.4. Sulphur sources .......................................................................................... 79
4.2.2.5. The influence of mineralelements on the growth of yeasts ........................ 81
4.2.2.6. The necessities in growing factors ............................................................. 82
4.2.3. Secondary fermentation products and their importance............................................. 83
4.2.4. Using immobilised yeasts in the alcoholic fermentation of beer and grape
must .............................................................................................................................89
5. Capitalizing the residual yeasts .................................................................................................... 91
5.1. Yeasts a valuable source of proteins and other active biological substances .91
5.1.1. Raw matters used in the production of proteins ......................................................... 93
5.1.2. Species of yeasts used in the protein industry .......................................................... 101
5.2. Yeast extracts ..............................................................................................................104
PART II - EXPERIMENTAL RESEARCH .....................................................................................111
6. Materials and methods ............................................................................................................... 112
6.1. Culture media..............................................................................................................115
6.2. Methods for the isolation and differentiation of the industrial yeasts .........................118
6.3. Morphological and physiological features of the yeasts used for the
identification ........................................................................................................................120
6.4. Tests used in the identification of the newly isolated industrial yeasts .................... 122
6.4.1. Microscopic examination ........................................................................................ 122
6.4.2. Producing ascospores .............................................................................................. 123
6.4.3. The examination of the culture characteristics
........................................................ 123
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6.4.3.1. Development on solid media ..................................................................... 123
6.4.3.2. Development in liquid media .................................................................... 125
6.4.4. Testing the capacity to assimilare the sugars for growth (auxanographic
method of Beijerinck)......................................................................................................... 126
6.4.5. Testing the fermentation capacity of the sugars ......................................................127
6.4.6. Testing the multiplication capacity ..........................................................................127
6.4.7. Osmosensitivity. Testing the growth at higher concentrations of D-glucose
and NaCl .............................................................................................................................128
6.4.8. Testing the capacity to use alcohol as a unique source of carbon ............................128
6.4.9. Testing the capacity to use azote from different salts as unique source of
azote ...................................................................................................................................129
6.4.10. Urease test...............................................................................................................129
6.4.11. Testing the growth in the presence of actidione (cycloheximide) ...........................130
6.4.12. Confirmation test of the oxidative yeasts (film yeasts) ...........................................130
6.5. Simplified procedure for the identification of the isolated contamination
yeasts ........................................................................................................................................ 130
6.6. Keys for the identification of the strains of isolated yeasts .............................................. 132
6.7. Methods and techniques for the biological study of yeasts .............................................. 135
6.7.1. Counting techniques ................................................................................................135
6.7.2. Techniques for assessing the metabolic activity of yeasts .......................................136
6.8. Analysis methods used for researching the technological properties of isolated
yeast strains ...............................................................................................................................137
6.8.1. Determining the alcoholic concentration of wort (beer and grape) in
fermentation........................................................................................................................138
6.8.2. Determining the concentration of the pristine wort (pristine extract) .................... 142
6.8.3. Determining the apparent and final extract of the wort ...........................................142
6.8.4. Determining the degree of wort fermentation..........................................................143
6.8.5. Determining the final degree of fermentation..........................................................144
6.8.6. Determining the flocculation capacity .....................................................................145
6.8.7. Determining the reducing sugars in stum and wine .................................................145
6.8.7.1. Determining sugar with the help of the refractometer ............................. 146
6.8.7.2. Determining the reducing sugar by applying theSchoorl method. 148
6.8.8. Determining the total acidity and the volatile acidity ..............................................150
6.8.8.1. Determining total acidity ......................................................................... 151
6.8.8.2. Determining the volatile acidity .............................................................. 152
6.8.9. Determining free and total sulfur dioxide ................................................................153
6.9. Adopted analysis methods for characterizing the residual yeasts and yeasts
extracts ..................................................................................................................................... 156
6.9.1. Determining the humidity and dry substance ..........................................................156
6.9.2. Determining the ash.................................................................................................157
6.9.3. Dosage of the lipids through the gravimetric analysis (Soxhlet method) ..158
6.9.4. Dosage of the total azote after rapid mineralization ................................................159
6.9.5. Gravimetric determination of the total tartrate content ............................................160
7. Results and discussions ......................................................................................................162
7.1. General features of the genera and species of yeasts with industrial applications. Spread and role
7.1.1. The Saccharomyces genus ....................................................................................... 162
7.1.2. The Candida Genus .................................................................................................. 164
7.1.3. The Pichia genus ...................................................................................................... 165
7.1.4. The Rhodotorula Genus ........................................................................................... 165
7.1.5. The Kloeckera genus ............................................................................................... 166
7.1.6. The Torulopsis genus ............................................................................................... 167
7.2. Isolation in pure cultures of certain industrial yeast strains ............................................... 168
7.3. Biological properties of isolated industrial yeast strains ................................................... 173
7.3.1. Morphological characteristics .................................................................................. 173
7.3.2. Physiological traits ................................................................................................... 190
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7.3.2.1. The fermentation capacity of various sugars .............................................. 190
13.2.2. The capacity to assimilate various sugars and other organic carbon compounds
7.3.2.3. The capacity to use ethanol as unique source of carbon ............................. 198
7.3.2.4. The capacity to use nitrogen from various compounds as unique
nitrogen source.......................................................................................................... 198
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7.3.2.5. The capacity of yeasts to produce urease ................................................... 201
7.3.2.6. The growth capacity of the studied yeasts in the presence of
actidione (cycloheximide) ........................................................................................ 201
7.3.2.7. Growth under higher concentrations of D-glucose and NaCl.
Osmosensitivity ........................................................................................................ 202
7.3.2.8. Testing the resistance to preservatives and the yeast growth at high
temperatures (37°C).................................................................................................. 203
REFERENCES................................................................................................................................. 205
Titlu: Biological and technological researches on some yeast strains
Autor: Letiția Oprean
Locul, editura, anul ediţiei: Ch.: ASEM, 2015
Cota: 66 /O-64
Localizare: Colecția în limbi străine (1 ex.)
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