Querol / Fleet Yeasts in Food and Beverages

1. Auflage 2006
ISBN: 978-3-540-28398-0
Verlag: Springer
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 453 Seiten, eBook

Reihe: The Yeast Handbook

As a group of microorganisms, yeasts have an enormous impact on food and bev- age production. Scientific and technological understanding of their roles in this p- duction began to emerge in the mid-1800s, starting with the pioneering studies of Pasteur in France and Hansen in Denmark on the microbiology of beer and wine fermentations. Since that time, researchers throughout the world have been engaged in a fascinating journey of discovery and development – learning about the great diversity of food and beverage commodities that are produced or impacted by yeast activity, about the diversity of yeast species associated with these activities, and about the diversity of biochemical, physiological and molecular mechanisms that underpin the many roles of yeasts in food and beverage production. Many excellent books have now been published on yeasts in food and beverage production, and it is reasonable to ask the question – why another book? There are two different approaches to describe and understand the role of yeasts in food and beverage production. One approach is to focus on the commodity and the technology of its processing (e. g. wine fermentation, fermentation of bakery products), and this is the direction that most books on food and beverage yeasts have taken, to date. A second approach is to focus on the yeasts, themselves, and their bi- ogy in the context of food and beverage habitats.

Zielgruppe

Research

Autoren/Hrsg.

Querol, Amparo

Fleet, Graham H.

Inhaltsverzeichnis

The Commercial and Community Significance of Yeasts in Food and Beverage Production.- Taxonomic and Ecological Diversity of Food and Beverage Yeasts.- Molecular Methods to Identify and Characterize Yeasts in Foods and Beverages.- Yeast Ecological Interactions. Yeast'Yeast, Yeast'Bacteria, Yeast'Fungi Interactions and Yeasts as Biocontrol Agents.- Physiological and Molecular Responses of Yeasts to the Environment.- Molecular Mechanisms Involved in the Adaptive Evolution of Industrial Yeasts.- Principles and Applications of Genomics and Proteomics in the Analysis of Industrial Yeast Strains.- Carbohydrate Metabolism.- Yeasts as Biocatalysts.- Production of Antioxidants, Aromas, Colours, Flavours, and Vitamins by Yeasts.- Food and Beverage Spoilage Yeasts.- The Public Health and Probiotic Significance of Yeasts in Foods and Beverages.- The Development of Superior Yeast Strains for the Food and Beverage Industries: Challenges, Opportunities and Potential Benefits.

Leseproben

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: [e-mail])
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: [e-mail])

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.

Über Autor(innen)

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.