Sourdough and Gluten-Free Products -- Sourdough and Cereal Beverages -- Bread and leavened bakery products have been essential to human nourishment for millennia.
Handbook on Sourdough Biotechnology
Traditionally, bread production has relied on the use of sourdough as a leavening agent and to impart a characteristic quality to baked goods. In recent years, improved understanding of the biodiversity and microbial ecology of sourdough microbiota, the discovery of new species, and the commercialization of innovative products have vastly expanded the potential of sourdough fermentation for the production of baked goods.
For example, raw materials such as cereals, pseudo-cereals, ancient grains, and gluten-free substrates, as well as a large number of baked good varieties e. In addition, biotechnological tools and culture properties have been discovered to improve both the shelf life and the sensory and textural qualities of baked goods, as well as their nutritional and health-promoting properties. Though sourdough has been and will remain a unique fermentation process, this is the first book dedicated completely to sourdough biotechnology.
It reviews the history of sourdough and the potential of sourdough fermentation in the production of bread and baked goods. A thorough discussion of the various processing steps includes the chemical properties of the raw matter, the taxonomy, diversity, and metabolic properties of starter yeasts and lactic acid bacteria, and the effects of sourdough fermentation on the shelf life and the sensory, textural, nutritional, and health-promoting properties of baked goods.
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Log in to your account. Cereal dough is a dynamic system that is characterised by continuous changes in nutrient availability and changes in physico-chemical conditions. Depending on the type of flour and bread-making technology, starvation conditions can also be envisaged.
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The imbalance between yeast consumption and starch hydrolysis might lead to the rapid depletion of soluble carbohydrates. Overall, microbial starvation induces a quiescent state whose length is controlled by the presence of limiting factors. Yeast responds to a changing environment not with a small adjustment to key control points but with the coherent transcriptional regulation of large sets of genes.
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During the fermentation of sourdough yeast cells may encounter different environmental states. Co-fermentation with lactic acid bacteria and yeasts determines environmental fluctuations not only in terms of availability of nutrients, but also organic acid concentration, pH decrease and changes in the texture profile. Maintaining optimal functionality in the presence of such external variability is a central evolutionary constraint.
The exposure of microbial cells to stressful and fluctuating conditions during fermentation involves a broad transcriptional response with many induced or repressed genes. The selective pressure exerted by the environmental conditions encountered by yeast cells during sourdough fermentation, accounts for the consolidated dominance of selected yeast species, such as in particular C.
The microbial ecology of sourdough is likely modulated by two factors, nutrient availability or limitation. However, within the sourdough ecosystem there are numerous mechanisms whereby one species may influence the growth of another species. This chapter describes the stress response, of those species, to nutrient availability starvation , DY, pH acid stress , the presence of sugars, salts and polysaccharides osmotic stress , oxygen oxidative stress , temperature fluctuations heat shock and cold stress and interactions between lactic acid bacteria and yeasts e.
Moreover, both environmental process parameters and the interaction with lactic acid bacteria affect the metabolism of yeast in terms of fusel alcohols and specifically branched-chain amino acid metabolites, carbonyl compounds and unsaturated fatty acid oxidation products, and also induce the production of inter-species signalling molecules. Elisabetta Guerzoni, Diana I. Serrazanetti, Pamela Vernocchi, Andrea Gianotti.
In the past decades, studies on the physiology and biochemistry of sourdough lactic acid bacteria provided insight into the microbial ecology of sourdough as well as the effect of the metabolic activity of lactic acid bacteria on flavor, texture, shelf-life, and nutritional properties of leavened baked goods. Lactic acid bacteria are the dominant microorganisms of sourdough.
Their metabolic versatility favors adaptation to the various processing conditions and the metabolic interactions with autochthonous yeasts determine mechanisms of proto-cooperation during sourdough fermentation [1—3]. Lactobacillus species are most frequently found in sourdough fermentations although species belonging to the genera Pediococcus , Enterococcus , Lactococcus , Weissella and Leuconostoc were also identified [4—6], see Chap.
A large number of Lactobacillus species were first identified from sourdoughs or fermentation processes of cereals . This chapter gives an overview of the general growth and stress parameters, carbohydrate and amino acid metabolism, synthesis of exopolysaccharides and antimicrobial compounds, and the conversion of phenolic compounds and lipids of lactic acid bacteria during sourdough fermentation. The quality of bread is characterized by its flavor, nutritional value, texture, and shelf life .
In the baking industry, these characteristics are improved by addition of bread improvers or enzymes. Alternatively, the addition of sourdough influences all aspects of bread quality and thus meets consumer demands for a reduced use of additives. Since sourdough is an intermediate but not an end product the microbiological activity has to be determined on the bases of their impact on bread quality.
Biochemical changes during sourdough fermentation occur in protein and carbohydrate components of the flour. The rate and extent of these changes greatly influence the properties of the sourdough and consequently the quality of the bread dough and bread structure.
The effects are associated with the metabolites produced by lactic acid bacteria LAB and yeast during fermentation, including organic acids, exopolysaccharides EPS , enzymes, and CO 2. The following chapter presents the impact of sourdough fermentation on structure-forming components of bread, and bread texture.
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- Handbook on sourdough biotechnology.
Sourdough fermentation is best known and most studied for its effects on the sensory quality and shelf life of baked goods. Acidification, activation of enzymes and their effects on the cereal matrix as well as production of microbial metabolites all produce changes in the dough and bread matrix that also influence the nutritional quality of the products. The nutritional quality is formed through the chemical composition and structure of the fermented foods, i. Sourdough fermentation can change all of these, as previously reviewed by Poutanen et al.
Over the last years, sourdough has received increasing interest as an alternative, natural and low-cost tool for improving the quality of gluten-free GF bread.
Marco Gobbetti (Author of Handbook on Sourdough Biotechnology)
The textural, nutritional and sensory benefits deriving from the use of sourdough in bread arise from the metabolic activities of the sourdough-resident lactic acid bacteria and yeasts. A deep understanding of the microbiological complexity and its influence on the technological properties of GF materials is a pre-requisite for setting guidelines for the successful application of GF sourdough in GF bread. This chapter will give a comprehensive review of the latest outcomes on the characterization of the microbial diversity of GF fermentations and on the applications of GF sourdough in GF breads.
Cereal-based fermented beverages are traditionally used as staple foods and consumed in certain geographical regions. One of the main advantages of the fermented products is the increased mineral availability due to the phytate elimination during fermentations. Further development of the traditional beverage fermentations at an industrial scale could improve the nutritional quality of the products as well as their sensory properties. This chapter focuses on traditional cereal-based non-alcoholic fermented beverages and introduces products that differ in their manufacturing concepts.
The microbial composition and manufacturing processes of the beverages as well as their functions are presented in a concise manner.