Elsevier

Food Microbiology

Volume 24, Issue 2, April 2007, Pages 165-174
Food Microbiology

Impact of sourdough on the texture of bread

https://doi.org/10.1016/j.fm.2006.07.011Get rights and content

Abstract

Sourdough has been used since ancient times and its ability to improve the quality and increase the shelf-life of bread has been widely described. During sourdough fermentation, lactic acid bacteria (LAB) produce a number of metabolites which have been shown to have a positive effect on the texture and staling of bread, e.g. organic acids, exopolysaccharides (EPS) and/or enzymes. EPS produced by LAB have the potential to replace more expensive hydrocolloids used as bread improvers. Organic acids affect the protein and starch fractions of flour. Additionally, the drop in pH associated with acid production causes an increase in the proteases and amylases activity of the flour, thus leading to a reduction in staling. While improving the textural qualities of bread, sourdough fermentation also results in increased mineral bioavailability and reduced phytate content. In this review we will be discussing the effect of sourdough on wheat and rye bread as well as the potential of sourdough to improve the quality of gluten-free bread.

Introduction

The use of the sourdough process as a form of leavening is one of the oldest biotechnological processes in food production (Röcken and Voysey, 1995). Its main function is to leaven the dough to produce a more gaseous dough piece and as such a more aerated bread. In recent years the traditional sourdough bread production has enjoyed renewed success with the ever increasing demand by the consumer for more natural, tasty and healthy foods (Brummer and Lorenz, 1991). Early dough fermentation would probably have relied on a mixture of natural yeasts and lactic acid bacteria (LAB) (Oura et al., 1982; Williams and Pullen, 1998). The underlying functionality of such an adventitious microbial population is that dough formed by the addition of water to ground cereals will be fermented by the micro-organisms naturally present to become a sourdough characterized by acid taste, aroma and increased volume due to gas formation (Hammes and Ganzle, 1998). In addition to the yeasts naturally present on the cereal grains, brewers’ yeast was often added to enhance the fermentation process (Oura et al., 1982; Röcken and Voysey, 1995; Williams and Pullen, 1998). Variations in the process parameters including temperature, dough yield as well as the amount and composition of starter cultures determine the quality and handling properties of sourdough (Barber et al., 1992). In wheat breads, sourdough is mainly used to improve flavour (Hansen and Hansen, 1996), however the addition of sourdough also has a major effect on the dough and the final bread structure. The utilisation of baker's yeast has not eliminated the use of sourdoughs in rye breadmaking, where a reduction in pH is necessary to achieve suitability for baking (Oura et al., 1982; Hammes and Ganzle, 1998; Salovaara, 1998). There is considerable consensus with regard to the positive effects of sourdough addition for bread production, including improvements in bread volume and crumb structure (Corsetti et al., 2000; Clarke et al., 2002; Crowley et al., 2002), flavour (Thiele et al., 2002), nutritional values (see Fig. 1; Liljeberg and Björck, 1994; Liljeberg et al., 1995) and shelf-life (Corsetti et al., 1998b; Lavermicocca et al., 2000, Lavermicocca et al., 2003; Dal Bello et al., 2006).

Section snippets

Understanding the technological functionality of sourdough application

Despite its long tradition and the well-documented positive effects conferred on bread products by its use, various details about sourdough technology have not yet been fully understood. This remains the case not only with regard to sourdough microbial ecology and physiology, despite much progress in this respect (Gobbetti, 1998; Hammes and Ganzle, 1998; Brandt, 2001), but also in relation to the influence of sourdough on the structure of dough and bread. Mechanisms at work in sourdough and its

Ecology of sourdough

As the texture parameters of the finished bread are determined by the microbial acidification and rate of substrate breakdown, it is important to characterize the micro-organisms responsible for those activities. The microbial ecology of the sourdough fermentation is determined by ecological factors (Hammes and Ganzle, 1998; Vogel et al., 1996). Endogenous factors are determined by the chemical and microbial composition of the dough, whereas exogenous factors are determined mainly by

Changes in the cereal protein fraction during sourdough fermentation

From a rheological point of view it is well established that as fermentation progresses there is a change in nature of the elements contributing to dough structure such as the decrease in the viscosity described for a gluten solution (Kawamura and Yonezawa, 1982). The protein fraction of wheat and rye flours is of crucial importance for bread quality. Proteolysis provides precursor compounds for the formation of aroma volatiles during baking as well as substrates for microbial conversion of

Application of exopolysaccharides (EPS) produced by sourdough LAB

The addition of plant polysaccharides is a common practice in the production of bread to improve textural properties and shelf-life of bread. Recently, the suitability of EPS produced by sourdough LAB to replace plant polysaccharides has been investigated. Two classes of EPS from LAB can be distinguished: extracellularly synthesized homopolysaccharides (HoPS) and heteropolysaccharides (HePS) with (ir)regularly repeating units that are synthesized from intracellular sugar nucleotide precursors.

Synergistic activity of sourdough and dough additives

Further to reliance on the integral components of dough, there is an increasing trend for the use of additives in the baking industry to achieve optimum functionality in terms of dough handling properties and bread quality attributes including shelf-life (Rosell et al., 2001). The interaction between sourdough and a number of additives such as exogenous enzymes and non-starch polysaccharides has been recently evaluated (Corsetti et al., 2000; Di Cagno et al., 2003). Corsetti et al. (2000) have

Bread texture and staling

The textural properties of a food have been described as “that group of physical characteristics that are sensed by the feeling of touch, are related to the deformation, disintegration, and flow of the food under the application of a force and are measured objectively by functions of force, time and distance” (Bourne, 1982). This is however an extremely restrictive meaning in relation to those properties that can be felt in the mouth or the hand and excludes physical characteristics such as

Rye sourdough

The introduction of baker's yeast has not eliminated the use of sourdoughs in rye breadmaking, where a reduction in pH is necessary to achieve suitability for baking (Oura et al., 1982; Hammes and Ganzle, 1998; Salovaara, 1998). The baking properties of rye and wheat flours differ in so far as rye flours contain high levels of pentosans. In rye doughs the proteins play a lesser role in the structure forming process than in wheat doughs, because the pentosans inhibit the formation of the gluten

Wheat sourdough

Whereas sourdough is an essential ingredient for ensuring baking properties of doughs containing more than 20% of rye flour, its addition to wheat doughs remains optional (Röcken, 1996). There is however a vast array of traditional products that rely on the use of sourdough fermentation in order to yield baked goods with particular characteristics. The use of LAB and yeasts in the form of sourdough is well established in Italy (Corsetti et al., 2001), Germany (Seibel and Brümmer, 1991), Spain (

Gluten-free sourdough

Coeliac disease (CD) is a chronic enteropathy caused by the intake of gluten proteins from widely prevalent food sources, such as wheat, rye, barley and possibly oats. The condition is exacerbated by the ethanol soluble storage proteins or prolamins from wheat, rye, barley and possibly oats. The ingestion of gluten induces an inflammatory response resulting in the destruction of the villous structure of the small intestine (Shan et al., 2002). CD results in malabsorption secondary to small

Conclusions

Sourdough has been used since ancient times and its ability to improve the quality and increase the shelf-life of bread has been widely described. There exist a myriad of microbial, technological and processing dimensions that must be considered in order to produce cereal products of optimum quality. Significant advances have been made in understanding the contributions made by the presence of acids, the fermentation period and the role played by cereal and bacterial enzymes in terms of

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