Food Biochemistry and Food Processing (Simpson/Food Biochemistry and Food Processing) || Bakery and Cereal Products

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31Bakery and Cereal Products

J. A. Narvhus and T. Sørhaug

IntroductionCereal Composition

StarchProtein

Gluten ProteinsEnzyme Proteins

AmylasesProteasesLipases

LipidsBread

Bread FormulationThe Development of Dough StructureDough Fermentation

Commercial Production of Baker’s YeastDesirable Properties of Baker’s YeastThe Role of Yeast in Leavened Bread

The Bread-Baking ProcessStaling

Sourdough BreadAdvantages of Making Sourdough BreadMicrobiology of SourdoughStartersSourdough ProcessesSelection and Biochemistry of Microorganisms in

SourdoughCarbohydrate MetabolismCo-metabolismProteolysis and Amino CompoundsVolatile Compounds and Carbon DioxideAntimicrobial Compounds from Sourdough LAB

Traditional Fermented Cereal ProductsThe Microflora of Spontaneously Fermented CerealsDesirable Properties of the Fermenting MicrofloraMicrobiological and Biochemical Changes in Traditional

Fermented CerealsFermented Probiotic Cereal FoodsReferences

INTRODUCTIONCereals are the edible seeds of plants of the grass family. Theycan be grown in a large part of the world and provide the staplefood for most of mankind. Maize, wheat, and rice contributeabout equally to 85% of world cereal production, which is atpresent about 2000 million tons (FAO 1999).

Cereals in their dry state are not subjected to fermentation dueto their low water content. Properly dried cereals contain lessthan 14% water, and this limits microbial growth and chemicalchanges during storage. However, on mixing grains or cerealflour with water or other water-based fluids, enzymatic changesoccur that may be attributed to the enzymes inherent in thegrain itself and/or to microorganisms. These microorganismscan either be those present as the natural contaminating flora ofthe cereal, or they can be added as a starter culture.

This chapter will be mainly devoted to fermented bakery prod-ucts made from wheat. However, on a global basis, many fer-mented cereal products are derived wholly or in part from othergrains such as rice, maize, sorghum, millet, barley, and rye.Different cereals differ not only in nutrient content, but also inthe composition of the protein and carbohydrate polymers. Thefunctional and sensory characteristics of products made fromdifferent cereals will therefore vary at the outset due to thesefactors. In addition to this, the opportunity to vary technologicalprocedures and microbiological content and activity providesus with the vast range of fermented cereal products that areprepared and consumed in the world today.

CEREAL COMPOSITIONCarbohydrates are quantitatively the most important constituentsof cereal grains, contributing 77–87% of the total dry matter.In wheat, the carbohydrate in the endosperm is mainly starch,whereas the pericarp, testa, and aleurone contain most of the

Food Biochemistry and Food Processing, Second Edition. Edited by Benjamin K. Simpson, Leo M.L. Nollet, Fidel Toldra, Soottawat Benjakul, Gopinadhan Paliyath and Y.H. Hui.C© 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

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31 Bakery and Cereal Products 595

crude and dietary fiber present in the grain. The pericarp, testa,and aleurone also contain over half of the total mineral matter.Whole meal flour is derived, by definition, from the whole grainand contains all its nutrients. When wheat is milled into flour, theyield of flour from the grain (extraction rate) reflects the extentto which the bran and the germ are removed and thereby deter-mines not only the whiteness of the flour, but also its nutritivevalue and baking properties. Decreasing extraction rate resultsin a marked, and nutritionally important, decrease in fiber, fat,vitamins, and minerals (Kent 1983). The protein content of dif-ferent cereal grains varies between 7% and 20%, governed notonly by cereal genus, species, or variety (i.e., genetically regu-lated), but also by plant growth conditions such as temperature,availability of water during plant growth, and also of nitrogenand other minerals in the soil. There is an uneven distributionof different protein types in the different parts of the grain, sothat although the protein concentration is not radically affectedby milling, the proteins present in different milling fractionswill vary.

Starch

The starch in cereals is contained in granules that vary in size,from 2–3 µm to about 30 µm according to grain species. Barley,rye, and wheat have starch granules with a bimodal size distri-bution, with large lenticular and small spherical grains. Almost100% of the starch granule is composed of the polysaccharidesamylose and amylopectin, and the relative proportions of thesepolymers vary not only according to species of cereal, but alsoaccording to variety within a species. However, both wheat andmaize contain about 28% amylose, but in wheat the ratio ofamylose to amylopectin does not vary (Fenema 1996, Hoseney1998). The amylose molecule is essentially linear, with up to5000 glucose molecules polymerized by α-1,4 linkages and onlyoccasional α-1,6 linkages. Amylopectin is a much larger (up to106 glucose units) and more highly branched molecule with ap-proximately 4% of α-1,6 linkages that cause branching in theα-1,4 glucosidic chain.

During milling of grains, some of the starch granules becomedamaged, particularly in hard wheat. The starch exposed in thesebroken granules is more susceptible to attack by amylases andalso absorbs water much more readily. Therefore, the degreeof damage to the starch grains dictates the functionality of theflour in various baking processes. When water is added to starchgrains, they absorb water, and soluble starch leaks out of dam-aged granules. Heating of this mixture results in an increase inviscosity and a pasting of the starch, which on further heatingleads to gelatinization as the ordered crystalline structure is dis-rupted and water forms hydration layers around the separatedmolecules. The gelatinization temperature of starch from differ-ent cereals varies from 55◦C to 78◦C, partly due to the ratio ofamylose to amylopectin. The gelatinization of wheat starts atabout 60◦C. Despite the fact that there is not sufficient water tototally hydrate the starch in most bakery foods, the heat causesirreversible changes to the starch. On cooling a heated cerealproduct, some starch molecules reassociate, causing firming ofthe product.

Nonstarch polysaccharides, the pentosans, which are prin-cipally arabinoxylans, comprise approximately 2–3% of theweight of flour. They are derived from the grain cell walls andare polymers that may contain both pentoses and hexoses. Theyare able to absorb many times their own weight in water andcontribute in baking by increasing the viscosity of the aqueousphase, but they may also compete with the gluten proteins foravailable water. Cereals also contain small amounts (1–3%) ofmono-, di- and oligosaccharides, and these are important as anenergy source for yeast at the start of dough fermentation.

Protein

Cereal proteins contribute to the nutritional value of the diet,and therefore the composition and amount of protein present areinherently important. However, the protein content in cerealsalso has several important aspects in fermented bakery prod-ucts. The amount and type of some of the proteins is importantfor the formation of an elastic dough and for its gas-retainingproperties. Other proteins in cereals are enzymes with specificfunctions, not only for the developing germ, but also for var-ious changes that take place from the processing of flour tobakery products.

Gluten Proteins

The unique storage proteins of wheat are also the functionalproteins in baking. The gliadins and glutenins, collectively calledgluten proteins, make up about 80% of the total protein in thegrain and are mostly found in the endosperm. These proteinshave very limited solubility in water or salt solutions, unlikealbumins and globulins (Fig. 31.1). A good bread flour (known as“strong” flour) must contain adequate amounts of gluten proteinsto give the desired dough characteristics, and extra gluten maybe added to the bread formulation.

Enzyme Proteins

The albumin and globulin proteins are concentrated in the bran,germ, and aleurone.

Figure 31.1. Wheat proteins.

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596 Part 5: Fruits, Vegetables, and Cereals

Amylases The primary function of starch-hydrolyzing en-zymes is to mobilize the storage polysaccharides to read-ily metabolized carbohydrates when the grain germinates(Hoseney 1998).

α-Amylase hydrolyzes α-1,4 glycosidic bonds at random inthe starch molecule chain but is unable to attack the α-1,6 link-ages at the branching points on the amylopectin molecule. Theactivity of α-amylase causes a rapid reduction in size of the largestarch molecule, and the viscosity of a heated solution or slurryof starch is greatly decreased. It is most active on gelatinizedstarch, but granular starch is also slowly degraded.

β-Amylase splits off two glucose units (maltose) at a timefrom the nonreducing end of the starch chain, thus providing alarge amount of fermentable carbohydrate. β-Amylase is alsocalled a saccharifying enzyme since its action causes a markedincrease in sweetness of the hydrated cereal. Neither the hydrol-ysis of amylopectin nor of amylose is completed by β-amylase,since the enzyme is not able to move past the branching points.The presence of both α- and β-amylases, however, leads toa much more comprehensive hydrolysis, since α-amylase pro-duces several new reducing ends in each starch molecule.

The level of α-amylase is very low in intact grain but increasesmarkedly on germination, whereas β-amylase levels in intact andgerminated grain are similar.

Flour containing too much α-amylase absorbs less water andtherefore results in heavy bread. In addition, the dough is stickyand hard to handle, and the texture of the loaf is usually faulty,having large open holes and a sticky crumb texture. However,some activity is required, and bakers may add amylase eitheras an enzyme preparation or as wheat or barley malt in orderto slightly increase loaf volume and improve crumb texture.The thermal stability of amylases from different sources dictatestheir activity during the baking process. Microbial amylases withgreater thermal stability have been used in bread to decreasefirming (retrogradation) upon storage since these enzymes arenot fully denatured during baking.

Proteases Proteinases and peptidases are found in cereals, andtheir primary function is to make small amino nitrogen com-pounds available for the developing seed embryo during germi-nation, when the levels of these enzymes also increase. However,whether these enzymes have a role in bread baking is not certain.Peptidases may furnish the yeast with soluble nitrogen duringfermentation, and a proteinase in wheat that is active at low pHmay be important in acidic fermentations such as sourdoughbread.

Lipases Lipases are present in all grains, but oats and pearlmillet have a relatively high activity of lipase compared withwheat or barley (Linko et al. 1997). In flour of the former graintypes, hydrolytic rancidity of the grain lipids and added bakingfat may be a problem.

Lipids

Lipids are present in grains as a large number of different com-pounds, and they vary from species to species and also within

each cereal grain. Most lipids are found within the germ. Wheatflour contains about 2.5% lipids, of which about 1% are po-lar lipids (tri- and diglycerides, free fatty acids, and sterol es-ters) and 1.5% are nonpolar lipids (phospholipids and galactosylglycerides). During dough mixing, much of the lipid forms hy-drophobic bonds to the gluten protein (Hoseney 1998).

BREADMany different types of bread are produced in the world. Breadformulations and technologies differ both within and betweencountries due to both traditional and technological factors in-cluding: (1) which cereals are traditionally grown in a countryand their suitability for bread baking, (2) the status of bread inthe traditional diet, (3) changes in lifestyle and living standards,(4) globalization of eating habits, and (5) economic possibilitiesfor investing in new types of bread-making equipment.

The basic production of most bread involves the addition ofwater to wheat flour, yeast, and salt. Other cereal flours maybe blended into the mixture, and other optional ingredients in-clude sugar, fat, malt flour, milk and milk products, emulsifiers,and gluten (for further ingredients and their roles in bread, seeTable 31.1). The mixture is worked into an elastic dough thatis then leavened by the yeast to a soft and spongy dough thatretains its shape and porosity when baked. An exception to thisis the production of bread containing 20–100% rye flour, wherethe application of sourdough and low pH are required.

Bread Formulation

The formulation of bread is determined by several factors. Ina simple bread, the baking properties of the flour are of vitalimportance in determining the characteristics of the loaf usinga given technology. In addition, the bread obtained from usingpoor bread flour or suboptimum technology may be improvedby using certain additives (Table 31.1).

The major methods used to prepare bread are summarized inFigure 31.2. In the straight dough method, all the ingredients areadded together at the start of the process, which includes twofermentation steps and then two proofing steps. In the spongeand dough method, only part of the dry ingredients are addedto the water, and this soft dough undergoes a fermentation ofabout 5 hours before the remainder of the ingredients are addedand the dough is kneaded to develop the structure. Althoughthese processes are time consuming, their advantages are thatthey develop a good flavor in the bread and that the timing andtechnology of the processes are less critical (Hoseney 1998).Mechanical dough development processes, such as the Chorley-wood bread process developed in the United Kingdom in the1960s, radically cut down the total bread-making time. The fer-mentation step is virtually eliminated, and dough formation isachieved by intense mechanical mixing and by various additivesthat hasten the process (Kent 1983). The resulting loaf has a highvolume and a thin crust but lacks flavor and aroma. The trendis now away from this kind of process due to customer demandfor more flavorful bread and reduced use of additives.

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Table 31.1. Bread Additives

Dough Additive Role

Cysteine. Sodium sulphite and metabisulphitea Reducing agent. Aids optimal dough development during mixing bydisrupting disulphide (–S–S–) bonds. A “dough relaxer.”

Amylase Releases soluble carbohydrate for yeast fermentation and Maillard browningreaction. Reduces starch retrogradation.

Ascorbic acid Oxidizing agent. Strengthens gluten and increases bread volume byimproving gas retention.

Potassium iodate, calcium iodate; calciumperoxide; azodicarbonamidea

Fast-acting oxidants; oxidizes flour lipids, carotene and converts sulphydryl(–SH) groups to disulphide (–S–S–) bonds.

Potassium and calcium bromatesa Delayed-acting oxidants: Develops dough consistency, reduces proofingstage.

Emulsifiers, strengtheners/conditioners andcrumb softeners

Dispersion of fat in the dough. Increase dough extensibility. Interact with thegluten-starch complex and thereby retard staling.

Soy flour Increases nutritional value, bleaches flour pigments, increases in loafvolume, increases crumb firmness and crust appearance, promotes alonger shelf life.

Vital wheat gluten and its derivatives Increases gluten content, used especially when mixing time or fer- mentationtime is reduced. Water adsorbant. Improves dough and loaf properties.

Hydrocolloids: Starch-based products fromvarious plants

Regulates water distribution and water-holding capacity and therebyimproves yield. Strengthens bread crumb structure and improvesdigestibility.

Cellulose and cellulose-based derivatives Source of dietary fiber.Salt Enhances flavor (ca. 2% based on flour weight) and modifies mixing time

for bread and rolls. Increases dough stability, firmness and gas retentionproperties. Raises starch gelatinization temperature

Source: Compiled from Stear 1990, Williams and Pullen 1998.aNot allowed in all countries.

Figure 31.2. Bread-processing methods. (Adapted from Hoseney 1994.)

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The Development of Dough Structure

When wheat flour and water are mixed together in an approx-imately 3:1 ratio and kneaded, a viscoelastic dough is formedthat can entrap the gas formed during the subsequent fermen-tation. The amount of water absorbed by the flour is dependentupon, and therefore must be adjusted to, the integrity of the starchgranules and the amount of protein present. A high proportion ofdamaged granules, as found in hard wheat flour, results in greaterwater absorption. The unique elastic property of the dough is dueto the nature of the gluten proteins. Hydrated gliadin is stickyand extensible, whereas glutenin is cohesive and plastic. Whenhydrated during the mixing process, the gluten proteins unfoldand bond with each other by forming a complex (gluten) askneading proceeds, with an increasing number of cross-linkagesbetween the protein molecules as they become aligned. Disul-phide bonds (-S-S-) break and re-form within and between theprotein molecules during mixing.

Gluten does not form spontaneously when flour and waterare mixed; energy must be provided (i.e., in the actual mixingprocess) in order for the molecular bonds to break and re-formas the gluten structure. At this point, the dough stiffens andbecomes smooth and shiny. The gluten is now composed ofprotein sheets in which the starch granules are embedded. Inaddition, free polar lipids and glycolipids are incorporated in thecomplex by hydrophobic and hydrogen bonds. The properties ofthe dough are determined by the amount of protein present andby the relative proportions of the gluten proteins.

Another important part of the dough formation is the incorpo-ration of air, in particular nitrogen. This forms insoluble bubblesin the dough that become weak points where carbon dioxidecollects during the subsequent fermentation step. In the Chor-leywood bread process, the dough is mixed under partial vacuumso that the incorporated bubbles expand and are then split intomany small ones as mixing continues, thus giving a fine-poredloaf crumb after baking.

Dough Fermentation

During the fermentation step, several processes happen simulta-neously, and in order to produce a bread of the required qualitycharacteristics, each of these processes must be optimized tothat end.

Yeasts have been used to leaven bread for thousands ofyears, but only in comparatively recent times have pure cul-tures of the yeast Saccharomyces cerevisiae been added to thebread dough as a leavening agent. The commercial productionof baker’s yeast follows procedures similar to those used inthe production of brewing, wine making, and distilling strainsof this same species. Indeed, the baking industry was orig-inally supplied with yeast waste from the brewing industryuntil about 1860 (Ponte and Tsen 1987). However, commer-cial production of yeast biomass specifically for the bakingindustry developed alongside an increasingly expanding man-ufacture of bread in commercial bakeries and the developmentof the technology that provided the great volumes required bythe industry.

Commercial Production of Baker’s Yeast

S. cerevisiae was originally produced commercially using grainmash as a growth substrate, but for economic reasons, it is nowgrown on sucrose-rich molasses, a by-product from the sugarcane or sugar beet refining industry. Nitrogen, phosphorous,and essential mineral ions such as magnesium are added topromote growth. The production of the yeast biomass for thebaking industry is multistage and takes about 10–13 hours at30◦C. S. cerevisiae shows the Crabtree effect, as its metabolismfavors fermentative metabolism at high levels of energy-givingsubstrate, thus resulting in a low production of biomass (Walker1998a). To avoid this, molasses is added incrementally towardthe end of the production of yeast biomass, and the mixture isvigorously aerated in order to promote respiration and avoidfermentative metabolism. At the end of the production, the yeastis allowed to “ripen” by aeration in the absence of nutrients. Thisstep synchronizes the yeast cells into the stationary growth phaseand also promotes an increase in the storage sugar trehalose inthe cells, thus improving their viability and activity.

When the fermentation is complete, the amount of yeast isabout 3.5–4% w/v. The biomass is separated and concentratedby centrifugation and filtering. The yeast cream is then pro-cessed into pressed yeast or is dried. The most usual types ofcommercial yeast preparations are (Stear 1990) the following:

� Cream yeast is a near liquid form of baker’s yeast thatmust be kept at refrigerated temperatures. It may be addeddirectly to the bakery product being made.

� Compressed yeast is formed by filtering cream yeast underpressure to give approximately 30% solids. It has a refriger-ated shelf life of 3 weeks.

� Active dry yeast (ADY) is produced by extruding com-pressed yeast through a perforated steel plate. The resultingthin strands are dried and then broken into short lengths togive a free-flowing granular product after further drying.Depending on the subsequent treatment and packaging,ADY may have a shelf life of over a year. However, ADYrequires rehydration before application in dough, and thiscan be a labor-intensive operation in a large bakery. Theproduct rehydrates best using steam or in water with addedsugar at 40◦C. Rehydration in pure water promotes leachingof cell contents and a reduction in the activity of the yeast.

� High activity dry yeast (HADY) (instant ADY, IADY) is asimilar product, where improved drying techniques are usedto give a product with smaller particle size that does notneed to be rehydrated before use and can therefore be incor-porated directly into bread dough without prior treatment.

Desirable Properties of Baker’s Yeast

Yeast plays a critically important role in leavened bread pro-duction, and over the decades of commercial production, strainshave been selected that give improved performance. Desirablecharacteristics include the following:

� High CO2 production during the dough fermentation due tohigh glycolytic rate.

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� The ability to quickly commence maltose utilization whenthe glucose in the flour is depleted.

� The ability to store high concentrations of trehalose, whichgives tolerance to freezing and to high sugar and saltconcentrations.

� Tolerance to bread preservatives such as propionate.� Viability and retained activity during various storage

conditions.

In the future, strains will probably be developed with evenmore useful properties. In particular, the flavor-forming proper-ties will receive special attention (Walker 1998b).

The Role of Yeast in Leavened Bread

When yeast is incorporated into the dough, conditions allow aresumption of metabolic activity, although there is little actualmultiplication of the yeast during shorter bread-making pro-cesses such as the straight dough and Chorleywood processes(Fig. 31.2). The yeast has been produced under aerobic (respi-ratory) conditions and is therefore adapted to this metabolism,but conditions very quickly become anaerobic in bread doughsince the oxygen incorporated in the dough is soon depleted.The sugars are metabolized to pyruvate by glycolysis; pyruvateis then decarboxylated to acetaldehyde, thus producing carbondioxide; and then ethanol is formed by reduction of acetaldehydeby NADH2 (Fig. 31.3). For each molecule of glucose (or halfmolecule of maltose) that is metabolized, two molecules eachof ethanol and carbon dioxide are produced. This fermentative

metabolism is the prevalent pathway in S. cerevisiae in doughdue both to the absence of oxygen and to the nonlimiting supplyof fermentable sugars (Maloney and Foy 2003).

The amount of maltose available is a complex interactionbetween the amount of damaged starch, the level of amylases inthe flour and the stage, and length of the fermentation process.Maltose accumulates during the early stages of the fermentationbecause it is generated by amylase but is not metabolized bythe yeast because the presence of glucose represses maltoseutilization.

When readily fermentable sugars (glucose and fructose) areexhausted, the yeast shows a lag in fermentation and then turnsits metabolism to the maltose produced from the action ofβ-amylase on starch. If sucrose has been added in the breadformulation (e.g., 4%), this is fermented in preference to mal-tose, and the lag in the fermentation may not be observed. Highamounts of added sucrose (e.g., 20%) significantly retard fer-mentation due to the high osmotic stress on the yeast (Maloneyand Foy 2003).

The products of yeast metabolism in dough fermentation varyconsiderably with pH. In bread, the pH is usually below 6.0,but above this, end products in addition to ethanol and CO2

are formed, such as succinate, acetic acid, and glycerol, and lessethanol and CO2 are formed. S. cerevisiae is also able to degradeproteins and lipids, and several flavor compounds are produced(Fig. 31.3).

It is generally not considered that the yeast fermentation isimportant for bread flavor and aroma development in traditional

Figure 31.3. Biochemical changes during yeast fermentation of bread.

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bread processes. However, the modern mechanical dough de-velopment processes, where the fermentation stage has beenradically reduced, produce bread with a flavor that is inferiorto that produced by the traditional straight dough process. Thisindicates that the yeast fermentation does make a positive con-tribution to bread flavor (Stear 1990). Zehentbauer and Grosch(1998) showed that yeast level and fermentation time and tem-perature affected aroma in the crust of baguettes, and they identi-fied the flavor compounds 2-acetyl-1-pyrroline (roasty), methylpropanal and 2- and 3-methylbutanal (malty), and 1-octene-3-ol and (E)-2-nonenal (fatty). An increase in fermentation timeallows for a development of flavor, but this trend is not reallynoticeable until much longer fermentation times are used, asin sourdough breads. There is not a clear borderline betweenregular bread and sourdough bread.

The production of ethanol and CO2 is essential for the devel-opment of the desired bread crumb structure, and several fac-tors affect both the development of the dough and its leavening(Fig. 31.4). During fermentation, some of the CO2 is lost to theatmosphere, but most either collects in the small pockets of airincorporated during dough mixing or is dissolved in the dough’saqueous phase. The amount that can be dissolved in the aqueousphase is dependent on temperature, and is greater at lower tem-peratures. As the aqueous phase is already saturated with CO2,it cannot escape from the bubbles by diffusion into the dough,so the bread begins to increase in volume. As the gas collects,the rheological properties of the dough allow it to expand inorder to equalize the pressure that builds up. Ethanol reacts withthe gluten to slightly soften it, allowing for easier expansion ofthe dough. It is important that CO2 develop immediately after

dough preparation and proceed at an adequate intensity. In ad-dition, the dough must have the physical properties necessaryto withstand dough manipulation and allow for gas retention, sothat the optimal structure has been obtained for the final proofand baking (Stear 1990).

The Bread-Baking Process

When the bread has undergone the final proofing and is put inthe oven, the outer surface rapidly starts to form the crust. Atemperature gradient develops due to transfer of heat from thepan to the loaf, and if the loaf is to achieve optimal properties,then the heat of the oven and the state of the bread proof needto be synchronized (Stear 1990). Apart from the outer crust,no part of the bread ever becomes dry; therefore, despite oventemperatures of well over 200◦C, the temperature in most ofthe loaf will not exceed 100◦C. The primary rise in tempera-ture increases the activity of the yeast, and its production ofCO2. At the same time, the solubility of CO2 decreases, ethanoland water evaporate, and the gases increase in volume. This re-sults in a marked increase in the volume of the dough, called“oven spring.”

As the temperature in the loaf continues to rise, several otherchanges take place. The yeast is increasingly inhibited, and itsenzymes are inactivated at about 65◦C. The amylases in thedough are active until about 65–70◦C is reached and a rapid in-crease in the amount of soluble carbohydrate takes place. Gela-tinization of starch occurs at 55–65◦C, and the water that thisrequires is taken from the gluten protein network, which thenbecomes more rigid, viscous, and elastic until a temperature is

Figure 31.4. Important factors for bread leavening.

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reached at which the protein begins to coagulate. At this stage,the structure of the dough has changed to a more rigid structuredue to denatured protein and gelatinized starch. These changesfirst occur near the crust and gradually move into the crumb asthe heat is transferred inward.

Toward the end of baking, the temperature at the crust ismuch higher than 100◦C. The crust becomes brown, and aromacompounds, predominantly aldehydes and ketones, are formed,mainly from Maillard reactions. The formation of flavor com-pounds is two staged. First, compounds are formed from thefermentation itself, and then during baking some of these com-pounds may react with each other or with the bread componentsto form other flavor compounds. Some other flavor compoundsformed during the fermentation may be lost due to the high tem-perature, but those that remain gradually diffuse into the crumbafter cooling. On further storage, the levels of flavor compoundsdecrease due to volatilization. Over 200 different flavor andaroma compounds have been identified in bread (Stear 1990).

Staling

The two main components of staling (firming of the bread crumb)are loss of moisture, mainly due to migration of moisture fromthe crumb to the crust (which becomes soft and leathery), and theretrogradation of starch. The major chemical change that occursduring staling is starch retrogradation, but a redistribution ofwater between the starch and the gluten also has been proposed.The gelatinization of the starch that occurs during cooking orbaking gradually reverses, and the starch molecules form in-termolecular bonds and crystallize, expelling water moleculesand resulting in the firming of crumb texture. Starch retrograda-tion is a time- and temperature-dependent process and proceedsfastest at low temperatures, just above freezing point. Since therearrangement of the starch molecules is facilitated by a highwater activity, staling is retarded by the addition of ingredientsthat lower water activity (e.g., salt and sugar) or bind water (e.g.,hydrocolloids and proteins). The staling rate can also be slowedby the incorporation of surfactants, shortening, or heat-stableα-amylase. Freezing of baked goods also retards staling sincethe water activity is drastically lowered. Much of the firming ofthe loaf during cooling is due to retrogradation of the amylosewhereas the slower reaction of staling is due, in addition, toretrogradation of amylopectin (Hoseney 1998, Stear 1990).

SOURDOUGH BREADWhen cereal flour does not contain gluten, it is not suitable forproduction of leavened bread in the manner described above.However, if rye flour, which is very low in gluten proteins, ismixed with water and incubated at 25–30◦C for a day or two,there is a good possibility that first step of sourdough productionwill be started. This mixture will regularly develop fermentationwith lactic acid bacteria (LAB) and yeasts. This forms the ba-sis of sourdough production, and this low-pH dough is ableto leaven.

The use of cereal flour and water as a basis for spontaneous ordirected fermentation products is common in many countries. In

Africa, fermented porridge and gruel as well as their diluted thirstquenchers, are the main products of these natural fermentations,whereas Europeans and Americans and their descendants enjoya variety of sourdough breads. In all these areas beers are alsoproduced.

This great variety of fermented products has an historic pro-totype in the earliest reported leavened breads in Egypt about1500 bc. Considering the simplicity of the process and the easewith which it succeeds, it has been suggested that peoples inseveral places must have shared this experience independently.It may be surmised that the experience with gruels and porridgepreceded the idea of making bread.

Common bread fermented only with yeast appeared later inour history, and it was a staple food in the Roman Empire. Thisalso indicates that the Romans had wheat with sufficient glutenpotential.

It is possible to make leavened bread without gluten usingsourdough, and this bread has become a favorite among manypeoples (Hammes and Ganzle 1998, Wood 2000).

Advantages of Making Sourdough Bread� Sourdough bread does not have to contain high levels of

gluten for successful leavening.� Low pH inhibits amylase, and thereby, degradation of

starch is avoided.� Sourdough improves the water-binding capacity of starch

and the swelling and solubility of pentosans.� Sourdough bread has very good keeping quality and an

excellent safety potential.� Less costly cereal flours can be used.� A different variety of flavor and taste attributes can be

offered.� Sourdough bread can nutritionally compete with regular

bread.� Phytic acid is degraded by phytase in flour and from lactic

acid bacteria. This improves the availability of iron andother minerals.

� Bread volume is increased, crumb quality is improved, andstaling is delayed.

Rye flour is very low in gluten proteins, and instead, starchand pentosans make an important contribution to bread struc-ture. The swelling and solubility of pentosans increase whenLAB fermentation lowers pH. Gelatinization of starch occurs atabout 55–58◦C. Considering that the flour amylase has a tem-perature optimum around 50–52◦C, it is crucial that the amylaseis actually inactivated in the pH range that is obtained duringsourdough fermentation. When mixtures of wheat and rye flourare used for bread making, a sourdough process is necessary ifthe content of rye flour exceeds 20%.

Rye and wheat flour contain phytic acid that binds miner-als, particularly iron, that then become nutritionally unavail-able. However, these cereals also contain phytases with pH op-tima around 5.0–5.5; thus, phytate degradation is very goodin fermented flour, where these phytate complexes are alsomore soluble. Lactic acid bacteria also appear to have somephytase activity.

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As wheat flour is able to form gluten, some of the consider-ations about amylases and starch are not equally relevant whenbaking wheat bread. Nevertheless, wheat flour is often used insourdough bread.

However, preferred qualities like improved keeping and safetypotential as well as the increased variety of flavors appeal tomany consumers. These desirable qualities are also praised be-cause they represent an alternative natural preservation method(Gobbetti 1998, Hammes and Ganzle 1998, Wood 2000).

Microbiology of Sourdough

An established, “natural” sourdough is dominated by a few rep-resentatives of some bacteria and yeast species. This resultsfrom the selective ecological pressures exerted in the (rye) flour-water environment. Rye flour is an appropriate choice for thismixture because leavening of the dough is dependent on sour-dough development. At the start of fermentation, a 50:50 (w/w)rye flour–water mixture at 25–30◦C will harbor approximatelythe following:

Mesophilic micro- 103–107 cfu/gorganisms, aerobes

Lactic acid bacteria <10 to 5 × 102 cfu/gYeast 10–103 cfu/gMolds 102 to 5 × 104 cfu/g

Among the mesophiles at the start, members of the Enterobac-teriaceae dominate. Microorganisms dominating in the sour-dough after 1–2 days at 25–30◦C are as follows:

Lactic acid bacteria 109 cfu/gYeast 106 to 5 × 107 cfu/g

Some important properties of the rye flour–water environmentdetermine that certain LAB and yeasts will compete most favor-ably. Lactobacilli have a superior ability to ferment maltose, theythrive despite limited iron due to the presence of phytic acid, andthey are able to grow at about pH 5.0 and lower.

Reports show that different LAB may be isolated from sour-doughs; however, Lactobacillus sanfrancis censis has beenfound most often. Table 31.2 presents some of the otherLactobacillus species that have been isolated from sourdough.The selection of yeasts may be even narrower, with Candidamilleri often cited (Table 31.2). Several other species are iso-

lated occasionally (Spicher 1983, Gobbetti and Corsetti 1997,Hammes and Ganzle 1998, Martinez-Anaya 2003, Stolz 2003).

Starters

It is traditional bakers’ practice to maintain a good sourdoughover time by regular transfer, for example, every 8 hours. Thisis called “rebuilding.” Such established cultures are referredto as Type I sourdoughs (Type I process), and a three-stagefermentation procedure is considered necessary to obtain anoptimal sourdough. Each step is defined by specific dough yield,temperature, and incubation time.

Dough yield is defined as:

(Flour + Water) by weight

Flour by weight= ×100 Dough yield

A high dough yield implies that a relatively large amount ofwater is used to make the dough; such a dough would conformwith certain requirements in industrial production when there isa need to pump the dough.

The lactobacilli and yeasts in Table 31.2 are all common insourdoughs; however, the composition of starter cultures forType I processes have been continuously stably maintained formany years, and may be compared to certain mixed culturesin dairy technology. The LAB and yeasts in such cultures willbe particularly well adjusted and adapted for the conditions insourdoughs. In Germany, established natural sourdough startercultures with a stable composition of Lb. sanfranciscensis andCandida milleri have been propagated for decades; they aremarketed as “Reinzuchtsauerteig.” When the sourdough processhas been started through a one-stage or a three-stage proce-dure, a part of the optimized dough is withdrawn to start upthe sourdough production for the next day. These sourdoughsare mentioned in different languages as Anstellgut (German),mother sponge (English), chef (French), masa madre (Spanish),madre (Italian).

Sourdoughs in Type II processes are used mainly for enhanc-ing the flavor and taste of the regular bread. Addition of baker’syeast is required for efficient leavening. Type I sourdoughs aregood alternatives as starters for the production of Type II sour-doughs. At the start of a production period, industrially largequantities of Type II sourdoughs may be stocked for portion-wise use over time.

Sourdoughs for Type III processes are dried sourdough prepa-rations.

Table 31.2. Common Representatives of Lactic Acid Bacteria and Yeasts Isolated from Mature Sourdoughs

Heterofermentative Homofermentative

Lactic acid bacteria Lactobacillus sanfranciscencis (formerly Lb.sanfrancisco, Lb. brevissubsp. lindneri) Lb. brevis, Lb. fructivorans, Lb. fermentum, Lb. pontis,Lb. sakei (formerly Lb. bavaricus, Lb. reuteri)

Lb. plantarumLb. delbrueckii

Yeasts Candida milleri, C. krusei, Saccharomyces cerevisiae, S. exiguusTorulopsis holmii, T. candida

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Defined cultures have also been marketed; however, the suit-ability of Type I and Type II cultures appears to outcompetethe alternatives offered. In addition to baker’s yeast, the col-lection of defined cultures comprise at least pure cultures ofLb. brevis (heterofermentative) and Lb. delbrueckii and Lb. plan-tarum (homofermentative). The homofermentative cultures pro-duce mainly lactic acid under anaerobic conditions, whereasthe heterofermentative cultures will also produce acetic acid orethanol and carbon dioxide. By controlling, if possible, the con-tributions from these different cultures, the relative amountsof acetic and lactic acids may be regulated. This importantrelationship:

Lactic acid (Mole)

Acetic acid (Mole)

is called the fermentation quotient (FQ).Relatively mild acidity will have an FQ about 4–9, whereas

a more strongly flavored rye bread, as produced in Germany,requires a much lower FQ, for example, 1.5–4.0 (Spicher1983, Gobbetti and Corsetti 1997, Hammes and Ganzle 1998,Martinez-Anaya 2003, Stolz 2003).

Sourdough Processes

Several more or less traditional sourdough processes arepracticed on a large scale in present-day bakery industry.(Fig. 31.5) One line comprises processes designed for bak-ing with rye flour. They may be the Type I processes men-tioned above. The Berliner short-sour process, the Detmolder

one-stage process, and the Lonner one-stage process are typ-ical for central and northern Europe. In every case, the pro-cess is initiated by a starter culture, 2–20% (often, 9–10%),in a rye flour–water (close to 50:50 w/w) mixture that is in-cubated for 3–24 hours at 20–35◦C, depending on the pro-cess. When the resulting sourdough is ready, bread makingstarts with an “inoculation” of about 30% sourdough togetherwith rye flour, wheat flour, baker’s yeast, and salt. The finalrye:wheat ratio is regularly 70:30 w/w. Dough yield is ad-justed to satisfy handling (e.g., pumping) and microbial nutritionrequirements.

Another line of sourdough processes comprises those for bak-ing with wheat only. The San Francisco sourdough process isoften mentioned in this connection; however, Italian wheat sour-dough products, for example, Panettone, Colomba, and Pandoro,are also very important (Cauvain 1998, Gobbetti and Corsetti1997, Spicher 1983, Wood 2000).

The starter for San Francisco sourdough is ideally rebuilt ev-ery 8 hours to maintain maximum activity. However, a maturesponge may be kept refrigerated for days with acceptable per-formance. For rebuilding the starter, sponge (40%) is mixedwith high-gluten wheat flour (40%) and water (about 20%) toferment at bakery temperature. Final bread making requires adough consisting of the ripe sourdough (9.2%), regular wheatflour (45.7%), water (44.2%), and salt (0.9%). Proofing for7 hours follows, during which the pH decreases from about 5.3 toabout 3.9. A sourdough starter culture for San Francisco Frenchbread production commonly contains Lb. sanfranciscensis andCandida holmii.

Figure 31.5. The sourdough process.

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Selection and Biochemistry ofMicroorganisms in Sourdough

Sourdough breads based on rye or wheat flour or their mix-tures enjoys a remarkable standing in many societies, eitheras established, traditional products or as “innovative” develop-ments for more natural products and a wider choice of flavors.Well-functioning and popular sourdough starters that have beenmaintained by simple rebuilding for decades, and the reestab-lishment of the “same” stable starter over and over again from aconstant quality flour, are both expressions of stable ecologicalconditions. The simplicity of the procedures may be somewhatdeceiving with respect to the actual complexity of these bi-ological systems. In the following sections, metabolic eventsand biochemical aspects of sourdough fermentation will be dis-cussed. Attention will be drawn to some of the more clear pointsabout the metabolic events and other biochemical facts. The nearfuture should bring us closer to a comprehensive understanding.

Carbohydrate Metabolism

The development of a mixture (1:1) of rye flour or even wheatflour with water incubated some hours at 25–30◦C will almost in-evitably lead to a microbiological population consisting of lacticacid bacteria (LAB) and yeasts. It may need rebuilding severaltimes in order to stabilize it, but from then on the composition ofthe microflora may be constant for years, provided the compo-sition of the flour and the conditions for growth are not changedmuch. Representative LAB and yeasts have been presented inTable 31.2. These microorganisms have certain characteristicsin common. First, the selected LAB are very efficient maltosefermenters, a prime reason why they competed so well in thefirst place. Several lactobacilli in sourdoughs, e.g. Lb. sanfran-ciscensis, Lb. pontis, Lb. reuteri, and Lb. fermentum, harbor akey enzyme, maltose phosphorylase, which cleaves maltose (thephosphorolytic reaction) to glucose-1-phosphate and glucose.Glucose-1-phosphate is metabolized heterofermentatively viathe phosphogluconate pathway, while glucose is excreted intothe growth medium. Glucose repression has not been observedwith these lactobacilli. Most of the yeast species identified insourdoughs are, per se, maltose negative, and will thus preferto take up glucose when it is available. Other microorganismsmay experience glucose repression of the maltose enzymes, tothe benefit of the sourdough lactobacilli. Among the yeasts, S.cerevisiae, which is maltose positive and transports maltose andhexoses very efficiently, cannot take up maltose due to glucoserepression and will, as a consequence, be defeated from the sour-dough flora. S. cerevisiae as baker’s yeast is, however, used atthe bread-making stage, but as an addition in the recipe. Addi-tional yeast cells may also be necessary for fast and efficient CO2

production, because the yeasts are relatively sensitive to acids,particularly to acetic acid, which is excreted by the heterofer-mentative lactobacilli that often dominate the LAB flora of thesourdough. Candida milleri (syn. S. exiguus, Torulopsis holmii)is common in sourdoughs for San Francisco French bread. Thisyeast tolerates the acetic acid from heterolactic fermentationand thrives on glucose and sucrose in preference to maltose; it

thus appears to be a near ideal partner for Lb. sanfranciscensis(Gobbetti and Corsetti 1997, Gobbetti 1998, Wood 2000,Hammes and Ganzle 1998).

Wheat and rye flour contain mainly maltose as a readily avail-able carbohydrate, although rye flour has greater amylase activ-ity and therefore has a greater potential for release of maltose.Early work in the United States on Lb. sanfranciscensis indi-cated that this organism would only ferment maltose (Kline andSugihara 1971). However, strains isolated in Europe appearedmore diversified, and some of them would ferment up to eightdifferent sugars (Hammes and Ganzle 1998). Utilization of mal-tose by Lb. sanfranciscensis, Lb. pontis, Lb. reuteri, and Lb.fermentum through phosphorolytic cleavage with maltose phos-phorylase is energetically very favorable (Stolz et al. 1993) andshows increased cell yield and excretion of glucose when mal-tose is available. In these conditions the cells have very lowlevels of hexokinase.

Co-metabolism

Lactobacilli in sourdough production are not only specializedfor maltose fermentation they also exploit co-fermentations foroptimized energy yield (Gobbetti and Corsetti 1997, Hammesand Ganzle 1998, Stolz et al. 1995, Romano et al. 1987). Lacto-bacillus sanfranciscensis, Lb. pontis and Lb. fermentum all havemannitol dehydrogenase. Thus, fructose may be used as an elec-tron acceptor for the reoxidation of NADH in maltose or glucosemetabolism, and then acetylphosphate may react on acetate ki-nase to yield ATP and acetate (Axelsson 1993). The lactobacilligain energetically and more acetic acid may contribute to thedesirable taste and flavor of bread. In practical terms addition offructose is used to increase acetate in the products, that is, lowerFQ (Spicher 1983). Comparable regulation of acetate produc-tion may be achieved by providing citrate, malate or oxygen aselectron acceptors, resulting in products like succinate, glyceroland acetate (Gobbetti and Corsetti 1996, Condon 1987, Stolzet al. 1993).

Proteolysis and Amino Compounds

In a sourdough, the flour contributes considerable amounts ofamino acids and peptides; however, in order to satisfy nutritionalrequirements of growing LAB and provide sufficient amino com-pounds, precursors, for flavor development, some proteolyticaction is necessary. The LAB have been suspected as the maincontributors of proteinase and peptidase activities for release ofamino acids in sourdoughs (Spicher and Nierle 1984, Spicherand Nierle 1988, Gobbetti et al. 1996), although the flour en-zymes may also have considerable input (Hammes and Ganzle1998). In addition, lysis of microbial cells, particularly yeastcells, add to the pool of amino acids; a stimulant peptide con-taining aspartic acid, cysteine, glutamic acid, glycine, and lysinethat appears in the autolytic process of C. milleri has also beenidentified (Berg et al. 1981). Lactobacillus sanfranciscensis hasbeen found to have a regime of intracellular peptidases, endopep-tidase, and proteinase, as well as a dipeptidase and proteinasein the cell envelope (Gobbetti et al. 1996). Limited autolysis of

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lactobacillus populations in sourdoughs may add to the reper-toire of enzymes that will release amino acids from flour pro-teins, including those from proline-rich gluten in wheat. Someof the enzymes have been purified for further characterization(Gobbetti et al. 1996), and they express interesting activity levelsat sourdough pH and temperatures.

The addition of exogenous microbial glucose oxidase, li-pase, endoxylanase, α-amylase, or protease in the productionof sourdough with 11 different LAB cultures showed positiveeffects on acidification rate and level for only three cultures, oneLeuconostoc citreum, one Lactococcus lactis subsp. lactis andone Lb. hilgardii. Lactobacillus hilgardii with lipase, endoxy-lanase or α-amylase showed increased production of acetic acid.Lactobacillus hilgardii interacted with the different enzymes forhigher stability and softening of doughs (Di Cagno et al. 2003).

Recent work with Lb. sanfranciscensis, Lb. brevis, and Lb. al-imentarius in model sourdough fermentations showed, by usingtwo-dimensional electrophoresis, that 37–42 polypeptides hadbeen hydrolyzed. The polypeptides varied over wide ranges ofpIs and molecular masses, and they originated from albumin,globulin, and gliadin, but not from glutenin. Free amino acidconcentrations increased, in particular those of proline and glu-tamic and aspartic acid. Proteolysis by the lactobacilli had apositive effect on the softening of the dough. A toxic peptidefor celiac patients, A-gliadin fragment 31–43, was degraded byenzymes from lactobacilli. The agglutination of human myel-ogenous leukemia–derived cells (K562) by toxic peptic-trypticdigest of gliadins was abolished by enzymes from lactobacilli(Di Cagno et al. 2002).

Volatile Compounds and Carbon Dioxide

Both yeasts and LAB contribute to CO2 production in sour-dough products, but the importance of the two varies. In breadproduction with only the (natural) sourdough microflora, theinput from LAB may even be decisive for leavening becausethe counts and kinds of yeast may not be optimal for gas pro-duction. Relatively low temperature (e.g., 25◦C) and low doughyield (e.g., 135) would select for LAB activities and less yeastmetabolism. More complete volatile profiles were obtained athigher temperatures (e.g., 30◦C) and with a more fluid dough.Of course, increasing the leavening time may give substantiallyricher volatile profiles (Gobbetti et al. 1995). If baker’s yeast,S. cerevisiae, is added to optimize and speed up the productionprocess, the contribution from yeasts will dominate (Gobbetti1998, Hammes and Ganzle 1998).

Bread made with chemical acidification without fermentationstarter failed in sensory analysis. This indicates that fermentationwith yeasts and LAB is important for good flavor, although highquality raw materials and proofing and baking are also decisivefactors. Flavor compounds distinguishing the different metaboliccontributions in sourdough are as follows (Gobbetti 1998):� Yeast fermentation (alcoholic): 2-methyl-1-propanol, 2,3-

methyl-1-butanol.� LAB homofermentative: diacetyl, other carbonyls.� LAB heterofermentative: ethyl acetate, other alcohols and

carbonyls.

Antimicrobial Compounds from Sourdough LAB

The primary antimicrobial compounds produced by sourdoughLAB are lactic and acetic acid, diacetyl, hydrogen peroxide, car-bon dioxide, and ethanol, and among these, the two organic acidscontinue to be the most important contributions for beneficialeffects in fermentations.

Researchers in the field, of course, also consider and testpossibilities that LAB may produce bacteriocins and other an-timicrobials. Thus antifungal compounds from Lb. plantarum21B have been identified, for example, phenyl lactic acid and4-hydroxyphenyl lactic acid (Lavermicocca et al. 2000). Caproicacid from Lb. sanfranciscensis also has some antifungal activity(Corsetti et al. 1998).

A real broad-spectrum antimicrobial from Lb. reuteri isreuterin (β-hydroxypropionic aldehyde), which comes as amonomer and a cyclic dimer (El-Ziney et al. 2000). Reuteri-cyclin, which was isolated from Lb. reuteri LTH2584 after thescreening of 65 lactobacilli, is a tetramic acid derivative. Reuteri-cyclin inhibited Gram-positive bacteria (e.g., Lactobacillus spp.,Bacillus subtilis, B. cereus, Enterococcus faecalis, Staphylococ-cus aureus, and Listeria innocua), and it was bactericidal towardsB. subtilis, S. aureus, and Lb. sanfranciscensis. The ability to pro-duce reutericyclin was stable in sourdough fermentations overa period of several years. Reutericyclin produced in sourdoughwas also active in the dough (Ganzle et al. 2000; Holtzel et al.2000; Ganzle and Vogel 2003).

A few bacteriocins or bacteriocin-like compounds have alsobeen identified, isolated, and characterized (Messens and DeVuyst 2002). Bavaricin A from Lb. sakei MI401 was selected byscreening 335 LAB strains, including 58 positive strains (Larsenet al. 1993). Bavaricin A (and Bavaricin MN from Lb. sakei MN)have the N-terminal consensus motif of bacteriocin class IIA incommon, comprise 41 and 42 amino acids, respectively, and haveinteresting sequence homologies and similar hydrophobic re-gions. Bavaricin A inhibits Listeria strains and some other Gram-positive bacteria but not Bacillus or Staphylococcus (Larsen et al.1993, Kaiser and Montville 1996). Plantaricin ST31 is producedby Lb. plantarum ST; it contains 20 amino acids, and the activityspectrum includes several Gram-positive bacteria but not Liste-ria (Todorov et al. 1999). A bacteriocin-like compound, BLISC57 from Lb. sanfranciscensis C57, was detected after screen-ing 232 Lactobacillus isolates, including 52 strains expressingantimicrobial activity. BLIS C57 inhibits Gram-positive bacteriaincluding bacilli and Listeria strains (Corsetti et al. 1996).

TRADITIONAL FERMENTEDCEREAL PRODUCTSOnly two cereals, wheat and rye, contain gluten and are therebysuitable for the production of leavened bread, but many otherfood cereals are grown in the world. On a global basis, a greatproportion of cereals are consumed as spontaneously fermentedproducts, in particular in Africa, Asia, and Latin America.Most fermented cereals are dominated by lactic acid bacteria(LAB), and the microflora associated with the grains, flour, orany other ingredient, together with contamination from water,

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food-making equipment, and the producers themselves, repre-sent the initial fermentation flora. Malted flour is also an im-portant source of microorganisms. The changes that take placeduring the fermentation are due to both the metabolism of the mi-croorganisms present and the activity of enzymes in the cereal,and these are in turn affected by the great variety of technolo-gies that are used. The technology may be simple, involvinglittle more than a mixing of flour with water and allowing itto ferment, or it may be extremely complex and involve manysteps with obscure roles. Indigenous fermented foods are usu-ally based upon raw materials that have a sustainable productionin their country of origin and are therefore attracting increasinginterest from researchers—both within pure and applied foodscience and also in anthropology. These ancient technologiesoften have deep roots in the culture of a country, and thereis increasing awareness of the importance of preserving thesetraditional foods. Many products are not yet described in theliterature, and knowledge of them is in danger of disappearing.It is therefore necessary to document the technologies used andto identify the fermenting organisms and the metabolic changesthat are essential for the characteristics of the product. It is, how-ever, often difficult to describe the sensory attributes of a productthat is inherently variable.

In Africa, as much as 77% of the total caloric consump-tion is provided by cereals, of which rice, maize, sorghum, andmillet are most important. Cereals are also significant sourcesof protein. Most of the cereal foods consumed in Africa aretraditional fermented products and are very important both asweaning foods and as staple foods and beverages for adults. InAsia, many products are based on rice, and maize is most widelyutilized in Latin America (FAO 1999).

Indigenous fermented cereals can be classified according toraw material, type of fermentation, technology used, productusage, or geographical location. They can range from quite solidproducts such as baked flat breads to sour, sometimes mildlyalcoholic, refreshing beverages.

Many factors have an influence on the characteristics of anindigenous product (Fig. 31.6). The choice of raw material maybe primarily influenced by price and availability rather than bypreference.

For instance Togwa, a Tanzanian fermented beverage, maybe made from maize in the inland areas of Morogoro andIringa, but from sorghum in the coastal areas of Dar es Salaamand Zanzibar (Mugula 2001). Similarly, the Ethiopian prod-uct borde may be made from several different grains accord-ing to availability—sorghum, maize, millet, barley and also theEthiopian cereal tef (Abegaz et al. 2002). The use of differentgrains obviously affects the sensory characteristics of a product,and yet it may have the same name throughout the country. Somefermented cereal products also contain other ingredients. Idli isa leavened steamed cake made primarily from rice to whichblack gram dahl is added. This not only improves the nutritionalquality, but in addition, the black gram imparts a viscosity, ap-parently specific for this legume, which may aid air entrapmentduring fermentation and thereby lighten the texture of the prod-uct (Soni and Sandu 1990). However, on a broader basis, theaddition of legumes such as soybean flour to fermented cereals

Figure 31.6. Important factors determining the characteristics ofspontaneously fermented cereal products.

has been suggested as an economically feasible way to generallyimprove the nutritional quality of cereal foods.

Some fermented cereal products are made using unmaltedgrain, with no extra addition of amylase, but they tend to ei-ther be very thick or of low nutritional density. Malted flouris added to many indigenous fermented cereals, a traditionaltechnology that has far-reaching effects on several product char-acteristics. The addition of malt provides amylases (in particular,α-amylase) that hydrolyze the starch, sweeten the product, andalso cause a considerable decrease in viscosity of the product af-ter heat treatment. The malting process, the germination of grainfollowing steeping in water, is associated with colossal micro-biological proliferation, and the organisms that develop duringmalting are a source of fermenting organisms. Many Asian prod-ucts, for example koji, a Japanese fermented cereal or soybeanproduct, are first inoculated with a fungus, as a source of amy-lase, in order to liberate fermentable sugars from the cereal starch(Lotong 1998).

Many fermented cereals are multipurpose. A single productmay be prepared in varying thicknesses and used as a fermentedgruel for both adults and children, or it may be watered downand used as a fermented thirst-quenching beverage. As Wood(1994) remarked, the latter type of product makes a meaningfulcontribution to nutrition; the potential of their replacement bycola-type beverages would result in a serious negative impact onthe nutrition of people in developing countries.

The use of fermented cereals as weaning foods in develop-ing countries raises several important issues. Unfermented gru-els deteriorate very rapidly in unhygienic conditions, especiallyif refrigeration is not available. They then represent a signif-icant source of foodborne infections that annually claim thelives of millions of young children (Adams 1998). Fermentedmalted cereal gruels have been shown on the whole to containlow numbers of pathogenic organisms since these are inhibitedand killed by the low pH that rapidly develops in the product.

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Fermented cereals are therefore usually regarded as safer thantheir unfermented counterparts (Nout and Motarjemi 1997). Aweaning food made from unmalted cereals may be a cause ofmalnutrition because its thick viscosity limits the nutritional in-take of a small child. Addition of malted flour decreases the vis-cosity so that more food can be ingested. If the fermentation floraincludes yeasts in addition to LAB, a measurable reduction ofcarbohydrate will occur due to the production of CO2 and othervolatile compounds (Muyanja 2001). Analysis of fermented ce-real products therefore shows that the protein:carbohydrate ratiois improved during the fermentation, and this obviously has nu-tritional benefits.

Milling of cereals into flour is usually done prior to fermen-tation, but in some products, for example, borde (Ethiopia), wetmilling is used. This technique can be used when mechanicalgrain mills are not available and if the product is required tobe smooth and without bits of suspended bran. The starch isalso liberated from the grain more thoroughly when slurriedwith water and sieved than if it has been previously dry milled(Abegaz 2002).

A heat treatment step is found at some point in the productiontechnology of most fermented cereal products and may involveboiling, steaming, or roasting. The type of heating employed islikely to have an effect on the flavor of the product, certainly if thetemperature attained is sufficient to promote Maillard reactions.The heat also gelatinizes the starch, making it more suscepti-ble to amylolytic enzymes, thus providing greater amounts offermentable carbohydrates. However, at the same time, most ofthe natural contaminating (and potentially fermenting) flora andcereal enzymes are destroyed. Such products are also prone tocontamination after the heat treatment step, and are thereby po-tentially unsafe should pathogenic organisms grow during thesubsequent fermentation. The traditional solution to this is touse “backslopping,” the addition of some of a previous batch ofthe product, and/or the addition of malted flour. Regular back-slopping results in a selection of acid-tolerant organisms andfunctions as an empirical starter culture.

Fermentation usually takes place at ambient temperatures, andthis may cause seasonal variations in products due to selection ofdifferent microorganisms at different temperatures. The durationof fermentation is largely a matter of personal choice, based onexpected sensory attributes. Heat treatment after fermentationmakes for a safer product, but it has the disadvantage of changeof taste or loss of volatile flavor and aroma compounds.

The Microflora of SpontaneouslyFermented Cereals

Spontaneously acid-fermented cereal products may contain avariety of microorganisms, but the flora in the final productis generally dominated by acid-tolerant LAB. Yeasts are alsoinvariably present in large numbers when the fermentation isprolonged. A typical fermented cereal product contains approx-imately 109 and 107 cfu/g of product, of LAB and yeasts, re-spectively. However, since yeast cells are considerably largerthan bacteria cells, their metabolic contribution to product char-acteristics is likely to be just as important as that of the LAB.

The buffer capacity of cereal slurries is low, and the pH there-fore drops quickly as acid is produced. Pathogenic organismsare inhibited by a fast acid production, so the addition of startercultures, either as a pure culture or by “backslopping” promotesacid production and contributes to the safety of the fermentedproduct (Nout et al. 1989).

The potential and the need for upgrading traditional fermenta-tion technologies have initiated considerable research (Holzapfel2002). In some recent studies of spontaneously fermented ce-reals, the LAB and yeasts have been isolated and identifiedas a first stage towards developing starter cultures for small-scale production of traditional fermented cereals. Muyanja et al.(2003) recorded that bushera, a traditional Ugandan fermentedsorghum beverage that contains high numbers of LAB, wasusually consumed by children after one day of fermentationas “sweet bushera.” After 2–4 days, the product became sourand alcoholic and was consumed by adults. However, the sweetbushera showed very high counts of coliforms and had a repu-tation for causing diarrhea (Muyanja 2001). Clearly, the devel-opment of defined starter cultures would improve the safety ofthis and similar products.

Some recent examples of studies on the microbial flora ofspontaneously fermented cereals are shown in Table 31.3. Foreach product, several different types of organisms have beenisolated. In other words, a specific product is not produced fromfermentation by a specific organism or organisms. Lb. plantarumseems to be the most commonly isolated Lactobacillus species infermented cereals. In addition, heterofermentative LAB such asleuconostocs, Lb. brevis, and Lb. fermentum frequently occur.Yeasts are always present in spontaneously fermented prod-ucts, but few studies have characterized the predominatingspecies. However, Jespersen (2003) reported that S. cerevis-ciae is the predominant yeast in many African fermented foodsand beverages.

All spontaneously fermented products contain, or have con-tained, many different types of microorganisms. These havegrown in the product and will have metabolized some of thecereal components, thereby making a contribution (positive ornegative) with their metabolites to the overall sensory charac-teristics of that product. However, studies on spontaneously fer-mented products have focused on LAB and yeasts since theseorganisms are often associated with other, better known, fer-mented products and have a history of safe use in food. Stanton(1998) proposed that the nature of the substrate (raw material)and the technology used to produce fermented foods are thepredominating factors that determine the development of mi-croorganisms and, thereby, the properties of a product.

Desirable Properties of theFermenting Microflora

The most important property of a starter culture for a fermentedcereal is the ability to quickly produce copious amounts of lac-tic acid in order to achieve a rapid decline in pH and retardthe growth of pathogens and other undesirable organisms. Someworkers (Sanni et al. 2002) have sought amylolytic LAB strains,as this could remove the need for using the highly contaminated

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Table 31.3. Lactic Acid Bacteria and Yeasts Isolated from Some Traditional Fermented Cereal Products

Most Prevalent

Product (Countryof Origin) Cereal Basis Species of LAB Species of Yeast Reference

Togwa (Tanzania) Various Lb. brevis, Lb. cellobiosus, P. orientalis Mugula et al. 2003Lb. Plantarum S. cerevisiae

W. confusa C. pelliculosaP. pentosaceus C. tropicalis

Bushera (Uganda) Sorghum, millet Lb. brevis; E. faecium NR Muyanja et al. 2003Ln. mesenteroides

subsp. mesenteroidesOgi (Nigeria) Maize Lb. reuteri, Lb. Leichmanii, S. cereviseae and Ogunbanwo et al. 2003

Lb. plantarum, Lb. casei, Candida mycodermaLb. fermentum,Lb. brevis, Lb. alimentarius, Odunfa 1985Lb. buchneri, Lb. jensenii.

Pozol (Mexico) Maize Streptococcus spp., Omar and Ampe 2000Lb. plantarum,

Lb. fermentumLb. brevis C. mycoderma, Nuraida and others 1995Ln. mesenteroides S. cerevisiae,Lc. lactis, Lc. Rhodotorula spp.

raffinolactisBorde (Ethiopia) Various Lb. brevis NR Abegaz 2002

W. confusaP. pentosaceus

Idli (India) Rice and blackgrambeans

Leuconostocs spp. Saccharomyces spp. Soni and Sandu 1990Enterococcus faecalis

Note: Lb., Lactobacillus; Ln., Leuconostoc; L., Lactococcus; P., Pediococcus, E., Enterococcus; W., Weisella; S., Saccharomyces; I., Isa; NR, Notrecorded.

malted flour in a product. The starter should also be able to hy-drolyze the cereal protein in order to obtain the amino acidssufficient for rapid growth, and it should produce desirableand product-typical aroma and flavor compounds, but not off-flavors. Some products are characterized by a foaming consis-tency, and heterofermentative organisms (LAB or yeasts) arerequired for this property. Bacteriocin-producing strains havealso been sought (Holzapfel 2002) in an attempt to increase themicrobiological safety of the products. Starter cultures must alsobe commercially propagable and be able to survive preservationmethods without loss of viability, activity, or metabolic traits.

Microbiological and Biochemical Changesin Traditional Fermented Cereals

Few studies have been made on the biochemical changes thattake place in traditional fermented cereals. Mugula et al. (2003)analyzed samples of naturally fermented togwa made fromsorghum and maize, to which togwa was backslopped and maltwas added. The development of groups of microorganisms, or-ganic acids, soluble carbohydrates, and volatile components wasstudied during the 24-hour fermentation. Maltose and glucoseincreased during the first part of the fermentation due to the

action of cereal amylases, but later were reduced as the growthof LAB and yeasts increased. The pH dropped from around 5.0to 3.2 in 24 hours, and this was mirrored by a rise in lactic acidto about 0.5%. Ethanol and secondary alcohols and aldehydesincreased during the secondary part of the fermentation. Maltyflavors are typical for fermented cereal products and may be pro-duced during grain malting. Secondary aldehydes and alcoholsare responsible for these flavors and may also originate from mi-crobial metabolism of the branched-chain amino acids leucine,isoleucine, and valine. These compounds are produced by yeasts,some LAB, and probably also by other microorganisms inthe product.

Many spontaneously fermented cereals also have a very shortshelf life, since fermentation continues in the absence of refrig-eration. Off-flavors, in particular vinegary notes, are a commonproblem. The very low pH in fermented cereal products may besensorially compensated for by saccharification by β-amylase.

FERMENTED PROBIOTICCEREAL FOODSA probiotic food is a live bacterial food supplement, which wheningested, may improve the well-being of the host in a variety of

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ways by influencing the balance of the host’s intestinal flora(Fuller 1989). Most probiotic bacteria have been isolated fromthe healthy human intestine and are members of the genus Lac-tobacillus, but some products may contain Bifidobacterium spp.or the yeast Saccharomyces boulardii. While the potential bene-fits of probiotic bacteria have been generally accepted for manydecades, it is only in comparatively recent years that researchhas been able to scientifically document the beneficial medicaleffect due to some specific strains (Gorbach 2002). There isnow strong scientific evidence that specific strains of probioticmicroorganisms are able to:

� show a prophylactic action against and alleviate diarrheacaused by bacterial and viral infections, radiation therapy orthe use of antibiotics;

� suppress undesirable bacteria in the gut with beneficialresults for patients with conditions such as irritable bowelsyndrome and ulcerative colitis;

� influence the immune system, showing positive results forinfant atopic eczema and other allergies.

Indeed, in addition to the list above, other effects have beenproposed: the lowering of blood cholesterol; the prevention ofacute respiratory infections, Helicobacter pylori infections, andcolonization by potential pathogens in intensive care units inhospitals; relief of constipation; and a protection against thedevelopment of various forms of cancer. However, so far, con-vincing proof for the efficacy of probiotics against these prob-lems has not been obtained. The positive effects that have beendocumented have led to a great interest from food manufactur-ers and consumers alike. The main motivation for consumingprobiotic products is said to be the developing consumer trendtowards healthy living though natural foods and medicines anda trend away from the use of antibiotics and the incorporation ofchemical additives in food. As the beneficial effects of probioticfoods become scientifically accepted, there will be increasingpressure from food manufacturers on the authorities to allowhealth claims to be used in product advertising. Probiotic fer-mented milks were the first probiotic products to be produced

commercially and are available in many countries (Tamime andMarshall 1997).

Some fermented probiotic cereal products are now being pre-pared and marketed (Table 31.4) and may have an appeal forthose who do not consume dairy products.

Oats are a popular basis for probiotic cereal foods. This choiceis due to the healthy image of oats with respect to soluble andinsoluble fiber content and the potential to reduce blood choles-terol due to β-glucans. A prebiotic is a compound, usually anoligosaccharide, that reaches the colon undigested by the host’senzymes and selectively favors the growth of probiotic bacte-ria. Such compounds include lactulose, fructooligosaccharides,and inulin. It has been suggested that the best probiotic resultsmay be obtained by using a combination of a prebiotic (such asoats) and a probiotic organism (Charalampopoulos et al. 2002).In this way, the total physiological effect of the food could beincreased.

In order for a probiotic product to have a physiological effect,it has been suggested that it should contain at least 106 cfu/gproduct, and that daily intake should be at least 100 g (Sandersand Huis in’t Veld 1999). The final acidity in the product hasbeen shown to be of critical importance for the survival of probi-otic bacteria during storage (Martensson, Oste and Holst 2002).Many probiotic bacteria do not tolerate a pH below 4.0, and fer-mented cereals frequently reach this pH due to the poor bufferingcapacity of the substrate. In addition, the physiological state ofthe probiotic organisms at the time of storage also determinestheir survival. Organisms that show poor growth during a fer-mentation period are more likely to die out during cold storage.This necessitates careful formulation of the product as well asselection of the right probiotic culture.

The choice of a substrate for a probiotic food is partially gov-erned by the tolerance of the food towards heat pasteurizationor even sterilization before fermentation, and cereal mixtureslend themselves well to this treatment. Probiotic products re-quire fermentation at around 37◦C for 8–18 hours, dependingon substrate. The suitability of such conditions for the growthof pathogenic organisms necessitates strict adherence to hy-giene both before and during fermentation. A fast lactic acid

Table 31.4. Fermented Probiotic Cereal Foods

Type of Product(Commercial Name) Cereal Constituent Probiotic Constituent Reference

Fermented fruit flavoredcereal drink (Pro Viva)

Oat + malted barleyflour

Lb. plantarum 299v Molin 2001

Fermented cereal drink Oat “milk” LB. reuteri; lb.acidophilus;

Martensson, Osteand Holst 2002

B. bifidusFruit flavored cereal

pudding (Yosa)Oat flour Lb. acidophilus; B. bifidus Blandino et al. 2003

Cereal-based weaningfood

Maize + maltedbarley flour

Lb. acidophilus Helland et al. 2004Lb. rhamnosus ‘GG’Lb. reuteri

Note: LB = Lactobacillus; B = Bifidobacterium.

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development in the product during fermentation is a criticalstep, and the growth of probiotic organisms in cereal products isgreatly stimulated by the addition of malted flour (either of thesame grain or of barley malt) or milk, due to the increased avail-ability of fermentable sugars, peptides, and amino acids. Forprobiotic weaning foods, the use of malt has a further advantagesince at a given viscosity, the product has a higher nutritionalden-sity.

Probiotic cereal foods are in their infancy, and the future willprobably see further development in this type of product. Newstrains with proven probiotic efficacy and good flavor-formingabilities will increase the range of probiotic products available.

REFERENCES

Abegaz K. 2002. Traditional and Improved Fermentation of Borde,a Cereal-Based Ethiopian Beverage. [PhD thesis] Ås, Norway.Agric Univ of Norway. ISBN: 82-575-0508-0.

Abegaz K et al. 2002. Indigenous processing methods and rawmaterials of borde, an Ethiopian traditional fermented beverage.J Food Technol Africa 7: 59–64.

Adams MR. 1998. Fermented weaning foods. In: BJB Wood (ed.).Microbiology of Fermented Foods. Blackie Academic and Pro-fessional, London.

Axelsson LT. 1993. Lactic acid bacteria: classification and physiol-ogy. In: S Salminen, A von Wright (eds.). Lactic Acid Bacteria.Marcel Dekker, New York, pp. 1–63.

Berg RV et al. 1981. Identification of a growth stimulant for Lacto-bacillus sanfrancisco. Appl Env Microbiol 42: 786–788.

Blandino A et al. 2003. Cereal-based fermented foods and bever-ages. Food Res Int 37: 527–543.

Cauvain SP. 1998. Other cereals in breadmaking. In: Cauvain SP,Young LS (eds.), Technology of Breadmaking. Blackie Academicand Professional, London, pp. 330–346.

Charalampopoulos D et al. 2002. Application of cereal componentsin functional foods: a review. Int J Food Microbiol 79: 131–141.

Condon S. 1987. Responses of lactic acid bacteria to oxygen. FEMSMicrobiol Rev 46: 269–280.

Corsetti A et al. 1998. Antimould activity of sourdough lactic acidbacteria: Identification of a mixture of organic acids produced byLactobacillus sanfrancisco CB1. Appl Microbiol Biotechnol 50:253–256.

Corsetti A et al. 1996. Antimicrobial activity of sourdough lac-tic acid bacteria: Isolation of a bacteriocin-like inhibitory sub-stance from Lactobacillus sanfrancisco C57. Food Microbiol 13:447–456.

Di Cagno R et al. 2003. Interactions between sourdough lactic acidbacteria and exogenous enzymes: Effects on the microbial kinet-ics of acidification and dough textural properties. Food Microbiol20: 67–75.

Di Cagno R et al. 2002. Proteolysis by lactic acid bacteria: Effectson wheat flour protein fractions and gliadin peptides involved inhuman cereal tolerance. Appl Env Microbiol 68: 623–633.

El-Ziney MG et al. 2000. Reuterin. In: AS Naidu (ed.). NaturalFood Antimicrobial Systems. CRC Press, London, pp. 567–587.

FAO. 1999. Fermented cereals. A Global Perspective. Food andAgricultural Services Bulletin No. 138. Food and AgricultureOrganization of the United Nations, Rome, Italy.

Fenema OR. 1996. Food Chemistry. Marcel Dekker, New York.Fuller R. 1989. Probiotics in man and animals. J Appl Bact 66:

365–378.Ganzle MG et al. 2000. Characterization of reutericyclin pro-

duced by Lactobacillus reuteri LTH2584. Appl Env Microbiol66: 4325–4333.

Ganzle MG, Vogel R. 2003. Contribution of reutericyclin productionto the stable persistence of Lactobacillus reuteri in an industrialsourdough fermentation. Int J Food Microbiol 80: 31–45.

Gobbetti M. 1998. The sourdough microflora: Interactions oflactic acid bacteria and yeasts. Trends Food Sci Technol 9:267–274.

Gobbetti M, Corsetti A. 1996. Co-metabolism of citrate and mal-tose by Lactobacillus brevis subsp. lindneri CB1 citrate-negativestrain: Effect on growth, end-products and sourdough fermenta-tion. Z Lebensmittel-Untersuchung und -Forschung 203: 82–87.

Gobbetti M, Corsetti A. 1997. Lactobacillus sanfrancisco a keysourdough lactic acid bacterium: A review. Food Microbiol 14:175–187.

Gobbetti M et al. 1995. Volatile compound and organic acid produc-tions by mixed wheat sour dough starters: Influence of fermen-tation parameters and dynamics during baking. Food Microbiol12: 497–507.

Gobbetti M et al. 1996. The proteolytic system of Lactobacillussanfrancisco CB1: Purification and characterization of a pro-teinase, dipeptidase and aminopeptidase. Appl Env Microbiol 62:3220–3226.

Gobbetti M et al. 1996. The sourdough microflora. Cellularlocalization and characterization of proteolytic enzymes in lac-tic acid bacteria. Lebensmittel-Wissenschaft und -Technologie 29:561–569.

Gorbach SL. 2002. Probiotics in the third millenium. Digest LiverDis 34: S2–7.

Hammes WP, Ganzle MG. 1998. Sourdough breads and relatedproducts. In: BJB Wood (ed.). Microbiology of Fermented Foods.Blackie Academic and Professional, London, pp. 199–216.

Helland M et al. 2004. Growth and metabolism of selected strains ofprobiotic bacteria, in maize porridge with added malted barley.Int J Food Microbiol 44: 957–965.

Holtzel A et al. 2000. The first low-molecular-weight antibioticfrom lactic acid bacteria: Reutericyclin, a new tetramic acid.Angewandte Chemie Int Ed 39: 2766–2768.

Holzapfel WH. 2002. Appropriate starter culture technologies forsmall-scale fermentation in developing countries. Int J Food Mi-crobiol 75: 197–212.

Hoseney RC. 1998. Cereal Science and Technology, 2nd edition.St. Paul, Minnesota: American Association of Cereal Chemists.

Jespersen L. 2003. Occurrence and taxonomic characteristics ofstrains of Saccharomyces cerevisiae predominant in African in-digenous fermented foods and beverages. FEMS Yeast Res 3:191–200.

Kaiser AL, Montville TJ. 1996. Purification of the bacteriocinbavaricin MN and characterization of its mode of action againstListeria monocytogenes Scott A cells and lipid vesicles. Appl EnvMicrobiol 62: 4529–4535.

Kent NL. 1983. Technology of Cereals, 2nd edition. Pergamon Press,Oxford.

Kline L, Sugihara TF. 1971. Microorganisms of the San Franciscosourdough bread process. II. Isolation and characterization of

P1: SFK/UKS P2: SFK



undescribed bacterial species responsible for souring activity.Appl Microbiol 21: 459–465.

Kunene NF et al. 2000. Characterization and determination of originof lactic acid bacteria from a sorghum-based fermented weaningfood by analysis of soluble proteins and amplified fragment lengthpolymorphism fingerprinting. Appl Environ Microbiol. 66: 1084–1092.

Larsen AG et al. 1993. Antimicrobial activity of lactic acid bacteriaisolated from sour doughs: Purification and characterization ofbavaricin A, a bacteriocin produced by Lactobacillus bavaricusMI401. J Appl Bacteriol 75: 113–122.

Lavermicocca P et al. 2000. Purification and characterizationof novel antifungal compounds from the sourdough Lacto-bacillus plantarum strain 21B. Appl Env Microbiol 66: 4084–4090.

Linko Y-Y et al. 1997. Biotechnology of bread baking. Trends FoodSci Technol 8: 339–344.

Lotong N. 1998. Koji. In: BJB Wood (ed.). Microbiology of Fer-mented Foods. Blackie Academic and Professional, London.

Maloney DH, Foy JJ. 2003. Yeast Fermentations. In: K Kulp,K Lorenz (eds.). Handbook of Dough Fermentations. MarcelDekker, New York.

Martensson O et al. 2002. The effect of yoghurt culture on thesurvival of probiotic bacteria in oat-based, non-dairy products.Food Res Int 35: 775–784.

Martinez-Anaya MA. 2003. Associations and interactions of mi-croorganisms in dough fermentations: Effects on dough and breadcharacteristics. In: K Kulp, K Lorenz (eds.). Handbook of DoughFermentations. Marcel Dekker, New York: pp. 63–95.

Messens W, De Vuyst L. 2002. Inhibitory substances produced byLactobacilli isolated from sourdoughs – a review. Int J FoodMicrobiol 72: 31–43.

Molin G. 2001. Probiotics in food not containing milk or milkconstituents, with special reference to Lactobacillus plantarum299v. Am J Clinical Nutr 73: 380S–385S.

Mugula JK. 2001. Microbiology, fermentation and shelf life exten-sion of togwa, a Tanzanian indigenous food. [PhD thesis]. Ås,Norway. Agric Univ of Norway. ISBN 82-575-0457-2.

Mugula JK et al. 2003. Use of starter cultures of lactic acid bacteriaand yeasts in the preparation of togwa, a Tanzanian fermentedfood. Int J Food Microbiol 83: 307–318.

Muyanja CBK. 2001. Studies on the Fermentation of Bushera : AUgandan Traditional Fermented Cereal-Based Beverage. [PhDthesis]. Ås, Norway, Agric Univ Norway. ISBN 82-575-0486-8.

Muyanja CBK et al. 2003. Production methods and compositionof bushera, a Ugandan Traditional Fermented Cereal Beverage.African J Food, Agric, Nutr Development 3: 10–19.

Muyanja C et al. 2004. Chemical changes during spontaneous andlactic acid starter bacteria starter culture fermentation of bushera.MURARIK Bulletin 7: 606–616.

Nuraida L et al. 1995. Microbiology of pozol, a Mexicanfermented maize dough. World J Microbiol Biotechnol 11:567–571.

Nout MJR, Motarjemi Y. 1997. Assessment of fermentation asa household technology for improving food safety: A jointFAO/WHO workshop. Food Control 8: 221–226.

Nout MJR et al. 1989. Effect of accelerated natural lactic fermenta-tion of infant food ingredients on some pathogenic microorgan-isms. Int J Food Microbiol 8: 351–361.

Odunfa SA. 1985. African Fermented Foods. In: BJB Wood (ed.).Microbiology of Fermented Foods, Vol, 2. Elsevier Applied Sci-ence Publishers, London and New York.

Ogunbanwo ST et al. 2003. Characterization of bacteriocin pro-duced by Lactobacillus plantarum F1 and Lactobacillus brevisOG1. African J Biotechnol 2: 219–227.

Omar benN, Ampe F. 2000. Microbial community dynamics duringproduction of the Mexican fermented maize dough Pozol. Appland Env Microbiol 66: 3644–3673.

Ponte JG, Tsen CC. 1987. Bakery Products. In: LR Beuchat, ed-itor. Food and Beverage Mycology, 2nd edition. Van NostrandReinhold Company, New York.

Romano AE et al. 1987. Regulation of β-galactoside transport andaccumulation in heterofermentative lactic acid bacteria. J ApplBacteriol 169: 5589–5596.

Sanders ME, Huis in’t Veld JHJ. 1999. Bringing a probiotic-containing functional food to the market: Microbiological, prod-uct, regulatory and labelling issues. In: WN Konings, OP Kuipers,Hui in T’Veld JHJ (eds.). Lactic Acid Bacteria: Genetics,Metabolism and Applications. Kluwer Academic Publishing,Dordrecht, The Netherlands, pp. 293–315.

Sanni AI et al. 2002. New efficient amylase-producing strains ofLactobacillus plantarum and L. fermentum isolated from differentNigerian fermented foods. Int J Food Microbiol 72: 53–62.

Soni SK, Sandu DK. 1990. Indian fermented foods. Microbiologicaland biochemical aspects. Indian J Microbiol. 30: 135–157.

Spicher G. 1983. Baked goods. In: HJ Rehm, G Reed (eds.). Biotech-nology, Vol. 5. Verlag Chemie: Weinheim, pp. 1–80.

Spicher G, Nierle W. 1984. The microflora of sourdough. XVIII.Communication: The protein degrading capabilities of the lac-tic acid bacteria of sourdough. Z fur Lebensmittel-Untersuchungund-Forschung 178: 389–392.

Spicher G, Nierle W. 1988. Proteolytic activity of sourdough bacte-ria. Appl Microbiol Biotechnol 28: 487–492.

Stanton WR. 1998. Food fermentation in the tropics. In: BJB Wood(ed.). Microbiology of Fermented Foods. Blackie Academic andProfessional, London, pp. 696–712.

Stear CA. 1990. Handbook of Breadmaking Technology. Barking,Elsevier Applied Science, United Kingdom.

Stolz P. 2003. Biological fundamentals of yeast and lactobacillifermentation in bread dough. In: K Kulp, K Lorenz (eds.).Handbook of Dough Fermentations. Marcel Dekker, New York:pp. 23–42.

Stolz P et al. 1993. Utilization of maltose and glucose by lac-tobacilli isolated from sourdough. FEMS Microbiol Lett 109:237–242.

Stolz P et al. 1995. Utilization of electron acceptors by lactobacilliisolated from sourdough. II. Lactobacillus pontis, L. reuteri, L.amylovorus, and L fermentum. Z fur Lebensmittel-Untersuchungund -Forschung 201: 402–410.

Todorov S et al. 1999. Detection and characterization of a novel an-tibacterial substance produced by Lactobacillus plantarum ST31isolated from sourdough. Int J Food Microbiol 48: 167–177.

Tamime AY, Marshall VME. 1997. Microbiology and technologyof fermented milks. In: BA Law (ed.). Microbiology and Bio-chemistry of Cheese and Fermented Milk. Blackie Academic andProfessional, London.

Walker GM. 1998a. Yeast technology. In: Yeast Physiology andTechnology. John Wiley & Sons, Inc: New York.

P1: SFK/UKS P2: SFK



Walker GM. 1998b. Yeast metabolism. In: Yeast Physiology andTechnology. John Wiley & Sons, Inc, New York.

Williams T, Pullen G. 1998. Functional ingredients. In: SP Cauvain,LS Young (eds.). Technology of Breadmaking. Blackie Academicand Professional, London.

Wood BJB. 1994. Technology transfer and indigenous fermentedfoods. Food Res Int 27: 269.

Wood BJB. 2000. Sourdough bread. In: RK Robinson, CA Blatt,PD Patel (eds). Encyclopedia of Food Microbiology. AcademicPress, San Diego, pp. 295–301.

Zehentbauer G, Grosch W. 1998. Crust aroma of baguettes II. De-pendence of the concentrations of key odorants on yeast level anddough processing. J Cereal Sci 28: 93–96.

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