Molecular Wine Microbiology

Alfonso V. Carrascosa Santiago, Rosario Munoz, Ramon Gonzalez Garcia, Alfonso V. Carrascosa Santiago, Rosario Munoz, Ramon Gonzalez Garcia

• Publisher: Academic Press
• Year: 2011
• ISBN:
  9780080962580
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Molecular Wine Microbiology features rigorous scientific content written at a level comprehensible for wine professionals as well as advanced students. It includes information on production and spoilage issues, the microbial groups relevant for wine production and microbial wine safety.

Microbiology has long been recognized as a key tool in studying wine production, however only recently have wine microbiology studies been addressed at a molecular level, increasing theunderstanding of how microbiology impacts not only the flavor quality of the wine, but alsoits safety. Understanding, at a molecular level, how a starter culture can impact ethanol, glycerol, volatile phenols, mannoproteins, biogenic aminesor ochratoxin A of a wine are just some of the core points that must be considered in order to achieve maximium consumer acceptability while addressing safety concerns during processing and storage. While other books offer insights into thetechnological aspects of enology, this book is written by expert microbiologists, who explore the positive and negative impacts of gene function in theproduction of wine, from a microbiological point of view.

• Winner of the 2012 Jury Award in Enology from the International Organisation of Vine and Wine
• Presents the most current methods of studying the microbiology of wine
• Includes latest identification and typing methods, reducing identification time from days and weeks to minutes and hours
• Provides important knowledge about the impact of microbiological factors at the molecular level for reduction of wine spoilage and increased wine quality and safety

Chapter 1. Saccharomyces Yeasts I

Primary Fermentation

Agustín Aranda¹, Emilia Matallana¹² and Marcel·lí del Olmo²

¹Departamento de Biotecnología, Instituto de Agroquímica y Tecnología de Alimentos, CSIC, Valencia, Spain

²Departament de Bioquímica i Biologia Molecular, Facultat de Ciències Biològiques, Universitat de València, Valencia, Spain

Outline

1. Yeasts of Interest in Wine Production2

1.1. Yeast Flora on the Grape, in the Winery, and in the Must2

1.2. Morphology and Cellular Organization of Yeasts3

1.3. Genetic Characteristics of Wine Yeasts4

2. Growth Characteristics of Saccharomyces Yeasts During Fermentation4

2.1. Must Composition4

2.1.1. Sugars5

2.1.2. Organic Acids5

2.1.3. Nitrogenous Compounds5

2.1.4. Polyphenols7

2.1.5. Mineral Salts7

2.1.6. Lipids7

2.1.7. Inhibitors7

2.2. Physical Parameters of Fermentation8

2.2.1. Temperature8

2.2.2. Aeration8

2.2.3. pH9

2.2.4. Clarification9

2.2.5. Carbon Dioxide9

2.3. Yeast Growth and Fermentation Kinetics9

2.4. Biochemistry of Fermentation10

2.4.1. Alcoholic Fermentation11

2.4.2. Nitrogen Metabolism12

2.5. The Importance of Yeast Metabolism in Wine Aroma14

3. Gene Expression During Fermentation17

3.1. Glycolytic Genes18

3.2. Osmotic Stress-response Genes19

3.3. Genes Induced During the Stationary Phase20

3.4. Gene Expression in Wine Yeasts Exposed to Specific Stress Conditions22

4. Genetic Improvement of Yeast Efficiency During Fermentation23

Certain naturally occurring strains of the yeast species Saccharomyces cerevisiae are the principal microorganisms responsible for the fermentation of grape must to obtain wine. In order to be able to optimize the winemaking process, we must have an understanding not only of the physicochemical properties of grapes and must and the environmental conditions of the winery, but also of the genetic, biochemical, and physiological characteristics of these yeasts. The conditions under which wine fermentation takes place generate multiple stresses to which the yeast must adapt, such as the high concentration of sugars in the must and the toxic levels of ethanol present in the final product. The metabolic and protective responses to these stresses during fermentation are one way in which these microorganisms have adapted to the biotechnological uses made of them, and the underlying molecular mechanisms provide an appropriate target for genetic and technological improvements.

1. Yeasts of Interest in Wine Production

1.1. Yeast Flora on the Grape, in the Winery, and in the Must

The fermentation of grape must is a complex microbiological process that involves interactions between yeasts, bacteria, and filamentous fungi (Fleet, 2007 and Fugelsang and Edwards, 2007). Yeasts, which play a central role in the winemaking process, are unicellular fungi that reproduce by budding. Most yeasts belong to the phylum Ascomycota on the basis of their sexual development. In these organisms, the zygote develops within a sac-like structure, the ascus, while the nucleus undergoes two meiotic divisions, often followed by one or more mitotic divisions. A wall forms around each daughter nucleus and its surrounding cytoplasm to generate four ascospores within the ascus. The ascus then ruptures and releases the ascospores, which can germinate and produce new vegetative cells. Although thousands of yeast species have been identified, only 15 correspond to wine yeasts (Ribéreau-Gayon et al., 2006).

Traditionally, wine has been produced using yeast strains found on the surface of grapes and in the winery environment. The yeasts reach the grapes by wind and insect dispersal and are present on the wines from the onset of fruit ripening (Lafon-Lafourcade, 1983). The predominant species on the grape is Kloeckera apiculata, which can account for more than 50% of the flora recovered from the fruit (Fugelsang & Edwards, 2007). Other species of obligate aerobic or weakly fermentative yeasts with very limited alcohol tolerance may also be found in lesser proportions. These belong to the genera Candida, Cryptococcus, Debaryomyces, Hansenula, Issatchenkia, Kluyveromyces, Metschnikowia, Pichia, and Rhodotorula (Fleet and Heard, 1993 and Ribéreau-Gayon et al., 2006). The fermentative species Saccharomyces cerevisiae and Saccharomyces bayanus are present in limited numbers. This microflora can be affected by a wide variety of factors, principally temperature, rainfall, altitude, ripeness of the crop, and use of fungicides (Boulton et al., 1996). The flora associated with winery equipment is largely made up of S. cerevisiae (Fleet and Heard, 1993Fleet, 2007 and Martini and Vaughan-Martini, 1990), though species of the genera Brettanomyces, Candida, Hansenula, Kloeckera, Pichia, and Torulaspora have also been isolated.

The yeasts present in the must during the first few hours after filling the tanks belong to the same genera as those found on the grapes, predominantly Hanseniaspora/Kloeckera. In these spontaneous vinification conditions, Saccharomyces yeasts (mainly S. cerevisiae) begin to develop after around 20h and are present alongside the grape-derived yeast flora. After 3 or 4d of fermentation, Saccharomyces yeasts predominate and are ultimately responsible for alcoholic fermentation (Ribéreau-Gayon et al., 2006). This change in the yeast population is linked to the increasing presence of ethanol, the anaerobic...