Yeasts in Food and Beverages (eBook)

Amparo Querol is a Research scientist in the Food Biotechnology Department of the Institute of Agrochemistry and Food Technology (Spanish Council for Scientific Research) and Assistant Professor Food Science and Technologiy at the University of Valencia, Spain. Her research interests include food biotechnology, genomics, systematics, phylogeny and molecular evolution of industrial yeasts. Graham Fleet is a Professor within the Food Science and Technology Unit, at the University of New South Wales. He has been active as a teacher and researcher in the fields of food microbiology, food biotechnology and yeast technology since 1975 and has authored numerous publications, reviews and books on the occurrence and significance of yeasts in food and beverage production.

Preface 6
Contents 8
1 The Commercial and Community Significance of Yeasts in Food and Beverage Production 10
1.1 Introduction 10
1.2 The Informative Process 11
1.3 Production of Fermented Foods and Beverages 11
1.4 Yeasts as Sources of Ingredients and Additives for Food Processing 13
1.5 Spoilage of Foods and Beverages by Yeasts 14
1.6 Yeasts as Biocontrol Agents 15
1.7 Public Health Significance of Yeasts in Foods and Beverages 16
1.8 Probiotic Yeasts 17
1.9 Future Prospects 17
References 17
2 Taxonomic and Ecological Diversity of Food and Beverage Yeasts 22
2.1 Introduction 22
2.2 Yeasts in Dairy Products 23
2.3 Yeasts in Fermented Sausages 26
2.4 Yeasts in Sourdough Breads 29
2.5 Yeasts in Grape Wines 33
2.6 Yeasts in Brewing 43
2.7 Yeasts in Other Alcoholic Beverages (Cider, Sherry Wine, Tequila) 45
2.8 Yeasts in Indigenous Foods, Beverages and Cash Crops 48
2.9 Collections of Food Yeast Cultures 51
References 52
3 Molecular Methods to Identify and Characterize Yeasts in Foods and Beverages 63
3.1 Introduction 63
3.2 Methods for Species Identification 65
3.3 Methods to Differentiate at Strain Level 74
Acknowledgements 83
References 83
4 Yeast Ecological Interactions. Yeast–Yeast, Yeast–Bacteria, Yeast–Fungi Interactions and Yeasts as Biocontrol Agents 91
4.1 Introduction 91
4.2 Ecological Interaction Between Microorganisms 92
4.3 Yeast Interactions in Foods and Beverages 96
4.4 Yeast Antagonism Applied as Biocontrol Agents in Preventing Plant-Spoilage Fungi 107
References 109
5 Physiological and Molecular Responses of Yeasts to the Environment 119
5.1 Introduction 119
5.2 Yeast Nutrition and Growth 120
5.3 Yeast Responses to Physical Stresses 128
5.4 Yeast Responses to the Chemical Environment 140
5.5 Summary and Conclusions 151
References 152
6 Molecular Mechanisms Involved in the Adaptive Evolution of Industrial Yeasts 161
6.1 Introduction 161
6.2 The Saccharomyces sensu stricto Complex Includes the Most Important Industrial Yeasts 162
6.3 Adaptive Evolution by “Genome Renewal” 163
6.4 Molecular Mechanisms Involved in the Generation of Evolutionary Novelties 164
6.5 Gross Chromosomal Rearrangements in Yeast Evolution 176
Acknowledgements 177
References 178
7 Principles and Applications of Genomics and Proteomics in the Analysis of Industrial Yeast Strains 183
7.1 Introduction 183
7.2 DNA Sequencing of Yeast Genomes 183
7.3 Whole Genome Approaches to the Characterisation of Industrial Strains of Yeasts 185
7.4 Genome Constitution of Industrial Strains of Yeasts 196
7.5 Analyses of the Industrial Process 208
7.6 Future Perspectives 214
References 215
8 Carbohydrate Metabolism 222
8.1 Introduction 222
8.2 Carbon Sources 222
8.3 Modes of Metabolism 223
8.4 Substrate Transport 224
8.5 Glycolysis 225
8.6 The Pentose Phosphate Pathway 231
8.7 Gluconeogenesis 232
8.8 Trehalose, Glycogen, and Cell Wall Glucans 233
8.9 Regulation 234
8.10 Metabolic Modelling and Functional Genomics 237
8.11 Concluding Remarks 239
References 239
9 Yeasts as Biocatalysts 250
9.1 Introduction 250
9.2 Immobilized Yeast Cells and Winemaking 257
9.3 Ethanol Production 261
9.4 Brewing 267
9.5 Fruit Wines 273
9.6 Cider 274
9.7 Vinegar 275
9.8 Dairy Products 277
9.9 Aroma 279
References 280
10 Production of Antioxidants, Aromas, Colours, Flavours, and Vitamins by Yeasts 291
10.1 Introduction 291
10.2 Background and Definitions 292
10.3 Concluding Remarks and Future Outlook 325
References 326
11 Food and Beverage Spoilage Yeasts 341
11.1 Introduction 341
11.2 Definitions 342
11.3 Which Foods are Prone to Yeast Spoilage? 344
11.4 Symptoms of Yeast Spoilage 346
11.5 Economic Effects of Yeast Spoilage 350
11.6 Which Yeasts Cause Spoilage and What are the Properties of the Successful Spoilage Yeasts? 352
11.7 Factors Comprising Preservation Systems 353
11.8 Spoilage Yeast Ecology 366
11.9 Future Trends in Yeast Spoilage 372
References 375
12 The Public Health and Probiotic Significance of Yeasts in Foods and Beverages 386
12.1 Introduction 386
12.2 Yeasts and Foodborne Gastroenteritis 387
12.3 Yeasts as Opportunistic Pathogens 388
12.4 Allergic and Other Adverse Responses to Yeasts 391
12.5 Yeasts as Probiotics 393
12.6 Other Health and Nutritional Benefits 395
12.7 Conclusion 395
References 396
13 The Development of Superior Yeast Strains for the Food and Beverage Industries: Challenges, Opportunities and Potential Benefits 403
13.1 Introduction: Who is Moulding Whom? 403
13.2 Genetically Engineering Yeasts for Improved Performance and Product Quality 408
13.3 GM Industrial Yeasts of the Future 430
13.4 General Conclusion 435
Acknowledgements 436
References 436
Index 449

Chapter 5 Physiological and Molecular Responses of Yeasts to the Environment (p. 111-112)

GRAEME M. WALKER 1 AND PATRICK VAN DIJCK 2

1 Division of Biotechnology &, Forensic Science, School of Contemporary Sciences, University of Abertay Dundee, Bell Street, Dundee DD1 1HG, UK (e-mail: g.walker@abertay.ac.uk)
2 Flanders Interuniversity Institute for Biotechnology, Department of Molecular Microbiology, VIB10, Laboratory of Molecular Cell Biology, K.U. Leuven, Institute of Botany &, Microbiology, Kasteelpark Arenberg 31, 3001 Leuven, Belgium (e-mail: patrick.vandijck@bio.kuleuven.be)

5.1 Introduction

Understanding the ways by which yeasts respond to changes in their physicochemical environment is very important in the food and beverage industries. For example, it is important for the maintenance of yeast viability and vitality in the production and utilisation of yeasts for food and fermentation processes, and it is additionally important for the control of yeasts that act as spoilage agents of foods and beverages. In the former situation, yeasts are confronted with several environmental stresses including insults caused by changes in temperature, pH, osmotic pressure, ethanol concentration and nutrient availability that individually or collectively can deleteriously affect yeast physiology. These changes may result in lowered yeast growth yield and impaired fermentation performance. In the case of food spoilage yeasts, such organisms have adapted to survive stress caused by low temperature and oxygen levels, anhydrobiosis and high salt/sugar concentrations and their effective elimination is often based on measures to counteract the inherent stress tolerance of these yeasts. Chapter 11 covers food spoilage yeasts in more detail.

The present chapter describes both physiological and molecular aspects of stress on yeast cells and will focus on yeasts’ responses to changes in their environment which are pertinent in situations where survival of the yeast is both desirable (e.g. industrial fermentations) and undesirable (e.g. foods and beverages spoilage). The stresses of particular relevance for the food industry are thermostress, pH shock, osmostress, nutrient starvation, ethanol toxicity, oxidative stress, prolonged anaerobiosis, and exposure to chemical preservatives. This chapter will not review biologically related stress factors in yeasts such as cellular ageing, genotypic changes and competition from other organisms, the last of these having been dealt with in Chap. 4.

5.2 Yeast Nutrition and Growth
5.2.1 General Comments About Cell Physiology of Important Food Yeasts

The premier industrial yeast Saccharomyces cerevisiae is widely employed in the production of foods and fermented beverages. As such, it is by far the most economically important microorganism known to mankind. The metabolic activities of S. cerevisiae have been exploited for millennia in the leavening of bread and in the fermentation of cereal wort and grape must – these activities will continue to be exploited for future millennia. Why has S. cerevisiae found such dominance in baking and alcoholic beverage production? The reasons lie both in the ability of numerous ""industrial"" strains of S. cerevisiae to effectively transform sugars into ethanol, carbon dioxide and numerous secondary flavour compounds and it’s ability to withstand stress caused primarily by temperature, osmotic pressure, ethanol toxicity and competitive bacteria and wild yeasts. Figure 5.1 summarises major stresses encountered by industrial fermentation (brewing) yeast strains. Of course, most yeasts are similarly able to ferment sugars, but they may not be able to tolerate the rigours of a large-scale industrial fermentation plant. S. cerevisiae is clearly able to do so and has found niches well-suited to it’s physiological behaviour in wineries and fermentation plants (Martini 1993, Vaughan-Martini and Martini 1995). In short, S. cerevisiae is arguably the most resilient industrial yeast that we currently have at our disposal. Nevertheless, new approaches to improve stress-tolerance of S. cerevisiae have been developed with potential benefits for food and beverage production processes (Chap. 13).

Stress-tolerance attributes in other yeast species also impact significantly in foods and beverages. Several non-Saccharomyces yeasts have also found beneficial production applications, whilst some species are detrimental after production in storage situations, especially with regard to yeast spoilage of high-sugar and high-salt foods. Some examples of stress-tolerant yeasts important in both food production and spoilage are listed in Table 5.1.