A Review of the Application of Sourdough Technology to Wheat Breads

History of Sourdough Technology: Bread in its many forms is one of the most staple foods consumed by humans (Cauvain, 1998a). The art and craft of bread making existed at the outset of recorded history and predates it, as documented by excavations undertaken in many parts of the world (Spicer, 1975). Depictions of the activities involved in the baking of bread have been found in tomb paintings from ancient Egypt, and one of the most detailed accounts of baking dates back to the reign of Seti I (1303-1290 b.c.) (Ezzamel, 1997). The purpose of bread making is to present cereal flours to the consumer in an attractive, palatable, and digestible form (Chamberlain, 1975). The earliest breads were likely unleavened or flat (Quail, 1996), but the first major technical innovation was the introduction of leavening, which yielded breads of superior palatability (Chamberlain, 1975). Early dough fermentation would probably have relied on a mixture of naturally occurring yeasts and lactic acid bacteria (Oura et al., 1982; Williams and Pullen, 1998). The underlying functionality of such an adventitious microbial population is that a dough formed by the addition of water to ground cereals will with time be fermented by the microorganisms naturally present to become a sourdough characterized by acid taste, aroma, and increased volume due to gas formation (Hammes and Gänzle, 1998). 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). To facilitate continuous production, one could save a portion of ripe sourdough dough to seed subsequent doughs, a process that continued into the nineteenth century (Williams and Pullen, 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), but the sourdough procedure predominated in bread making until specially prepared baker's yeast became available in the nineteenth century (Pederson, 1971). Use of Sourdough in Rye Products: The availability of baker's yeast has not eliminated the use of sourdoughs in rye bread making in which a reduction in pH is necessary to achieve suitability for baking (Hammes and Gänzle, 1998; Oura et al., 1982; Salovaara, 1998). This results from the inability of rye doughs to form a gluten network, which in wheat doughs provides the water-binding and gas-retaining properties. In rye, these functions are taken over by pentosans, whose solubility and swelling increase with a decrease in pH (Hammes and Gänzle, 1998). Sour conditions also partially inactivate the increased enzyme activity in rye flour, particularly amylase activity (Seibel and Brümmer, 1991). This is an important aspect, because the starch in rye gelatinizes at a relatively low temperature, 55-70 °C, which coincides with the temperature range for maximal α-amylase activity (Cauvain, 1998b). An excessive amount of α-amylase in rye flour produces not only a sticky crumb, but at higher levels, a very open grain, a reduction in loaf volume, and in some instances, cavitation of the loaf (Reed, 1966). The acidification also exerts positive effects on the structure of starch granules, leading to increased water-binding capacity (Hammes and Gänzle, 1998). Acidification of rye doughs improves their physical properties by making them more elastic and extensible and confers the acid flavor notes so characteristic of rye breads. Use of Sourdough in Wheat Products: Whereas sourdough is an essential ingredient for ensuring baking properties of doughs containing more than 20% rye flour, its addition to wheat doughs remains optional (Röcken, 1996). However, a vast array of traditional products rely on the use of sourdough fermentation to yield baked goods with particular quality characteristics. Some examples include the well-known Italian products associated with Christmas, Panettone, which originated in Milan (Sugihara, 1977), and Pandoro originally from Verona (Zorzanello and Sugihara, 1982) or their counterpart, Colomba, which is traditionally associated with Easter (Sugihara, 1977). San Francisco sourdough French breads (Kline et al., 1970) and soda crackers (Sugihara, 1985) are other examples of wheat products that rely on the process of souring. The same process is also used in the production of a number of flat breads, a typical example of which is the Egyptian baladi bread (Qarooni, 1996). Further to these traditional varieties of baked goods, the use of lactic acid bacteria and yeasts in the form of sourdough is well established in Italy (Corsetti et al., 2001), Germany (Seibel and Brümmer, 1991), Spain (Barber and Báguena, 1989a), and France (Infantes and Tourner, 1991). The use of sourdough in wheat breads has gained popularity as a means to improve the quality and flavor of wheat breads (Brümmer and Lorenz, 1991; Corsetti et al., 2000; Stear, 1990; Thiele et al., 2002).