Yeast Leaven Bread PDF

Yeast leaven bread Food processing Dr. Mohammed Alsebaeai  Food processing Techniques used to slow deterioration and allow people to enjoy foods in a variety of forms around the year and around the globe. Food processing turns raw agricultural product into attract...

Yeast leaven bread Food processing Dr. Mohammed Alsebaeai  Food processing Techniques used to slow deterioration and allow people to enjoy foods in a variety of forms around the year and around the globe. Food processing turns raw agricultural product into attractive and consumable food.  Importance of food processing to human health 1. Increases variety 2. Increases convenience 3. Improves quality of food  The most common five food processing methods Fermentation - Production of CO2 through anaerobic respiration, also produces lactic acid alcohol in the process. Canning - Sterilize food by getting it to a temperature of 212-250 F, then putting it into airtight containers. Dehydration - Lowers moisture content to inhibit growth of microorganisms. Irradiation - Uses gamma rays to kill insects, bacteria, fungi, etc. in food products. Blanching - Briefly scald food to inactivate enzymes that cause undesirable changes.  Yeast leavened bread The essential ingredients in yeast-leavened bread are: 1) wheat flour 2) water 3) yeast 4) salt Most bread produced in different countries incorporates small amounts of additional ingredients.  Yeast leavened bread White-pan bread It is most commonly produced bread in many countries These nonessential ingredients allow the baker to: compensate for flour deficiencies They may also add color or desirable flavor attributes that improve consumer acceptability. Nonessential ingredients 1. Sugar, shortening (fat), 2. Milk or milk products 3. Yeast foods 4. Surfactants 5. Enzymes, 6. Mold inhibitors WHITE-PAN BREAD WHITE-PAN BREAD VERSUS VARIETY BREADS White-pan breads are identified as Any bread, other than a variety bread. Variety bread formulations often include meals or grits with or without wheat flour. Whole wheat, rye, oats, barley, and millet are typical grain choices  The flavor and the crust and crumb characteristics of variety breads differ to varying degrees from white-pan breads. Production procedures also vary, with the extent to which variety bread production is similar to that of white- pan bread depending on the specific product being made. VARIETY BREAD WHITE-PAN BREAD QUALITY CRITERIA 1. Loaf volume, expressed as cubic centimeters/unit of weight, is the major criterion used to assess bread quality. 2. Loaf shape, height, and length and the relative proportions of loaf height and length are part of this quality assessment. 3. In white-pan breads, the loaf should have a rounded top without sharp corners or protruding sides and ends. 4. Crumb color should be a creamy white without streaks or spots. 5. Flavor, which includes both taste and aroma, should be pleasing and characteristic of the grain in the formulation; it is assessed subjectively.  Raw materials preparation Wheat flour comprises 55–60% of white-pan bread. Wheat flour characteristics are determined by : 1. The wheat(s) selected 2. The milling process 3. The treatments applied post milling. A. WHEAT SELECTION Selection among available wheats is based on the intended end use. Three commercially significant wheat species are important: 1. Triticum compactum (club wheat), which is used in cake and pastry flours 2. T. durum, which is used in pasta production 3. T. aestivum, is the preferred wheat species wherever yeast leavened breads and related dough-based products are produced.  Hard versus soft refers to 1. kernel characteristics 2. how tightly the starch granules are packed in the protein matrix  Relative hardness of the wheat kernels influences milling characteristics. Hard wheats exhibit greater resistance to grinding than soft wheats during the milling process. Hard wheats are higher than soft wheats in protein.  Red and white refers to kernel color, which is determined by whether or not there is a red pigment in the outer layers of the wheat kernel. Spring and winter refers to growth habit. The tests conducted on wheat prior to milling 1. Moisture 2. Bulk density 3. Protein 4. Sprout damage The results of these tests help the miller determine the blend characteristics. C. MILLING The wheat selected is milled with a dry process. When wheat arrives at the mill, it contains foreign material that will affect the 1. Appearance, 2. Functionality, 3. Mill operation. Cleaning occurs either before or after the blending process. Cleaning is usually a dry process involving several steps. 1. Magnets are used to remove ferrous materials; 2. a stoner removes foreign materials such as small stones and mud balls that differ in specific gravity from wheat. 3. A milling separator screens impurities that are larger and smaller than the wheat kernels, such as corn, mustard seeds, or soybeans. 4. Wheat kernels also undergo a dry scour. In this step, the wheat kernels are impelled against a screen to abrade the surface. This removes impurities in the crease, which are otherwise very difficult to eliminate.  The controlled addition of moisture for up to 36 hours, called tempering or conditioning. At a moisture content of about 15–16%, maximum milling efficiency and optimum performance of the resulting flour in the final product is achieved.  These corrugated break rollers rotate at different speeds in opposite directions, breaking the wheat kernel into coarse particles and thereby exposing the endosperm. The sheared and crushed kernels pass through a series of sieves that separates the material into three general size categories, 1. The coarsest fragments are sent through the next break, 2. The medium-sized particles are primarily endosperm and are known as middlings, 3. The finest particles are break flour.  After the fifth or sixth break, the remaining coarse particles are primarily bran. Most of the germ is removed by the third break. Finally, the medium-sized particles (middlings) from all the breaks are passed through a series of smooth reduction rolls. After each passage, in which the middlings are reduced in size and the adhering bran is loosened, the particles are sieved.  When all of the millstreams are combined, the resultant product is known as straight flour. One hundred pounds of cleaned wheat will yield about 72 pounds of straight flour and 28 pounds of byproducts; thus, there is a 72% extraction rate.  The by-products, also known as shorts, are 1. Bran 2. Germ 3. Some endosperm. The flour produced by milling is composed 1. Endosperm 2. Starch 3. Protein.  Separation of protein and starch Because the sizes of the protein and starch particles are very similar, sieving does not separate these fractions. Centrifugal force applied to the suspended particles yields two flour fractions that differ in starch and protein content. Postmilling treatments Postmilling treatment includes the incorporation of maturing and bleaching agents and enrichment. Oxidants such as benzoyl peroxide are added to bleach (whiten) the yellow pigments in the flour. Xanthophylls dominate the yellow pigments present.  Maturing agents 1. Potassium bromate (at levels less than 50 ppm), 2. Ascorbic acid (at levels less than 200 ppm), which accelerate the natural aging process of the flour and improve baking quality. Acetone peroxide, function as both bleaching and maturing agents.  Although both maturing and bleaching can be accomplished naturally by storing flours for several weeks to months. Flours may also be supplemented with enzymes, such as amylases and lipooxygenases, that improve their bread making performance.  Lipooxgenases, added as soy flour, function as bleaching agents and dough improvers. Addition of α-amylase, in the form of diastatic malt or a fungal supplement, corrects a flour deficiency. Enrichment, when added at the flour mill, is usually in the form of a premix containing the required nutrients. The five required nutrients include thiamine, riboflavin, niacin, iron, and folic acid. FLOUR SELECTION AND FUNCTIONALITY In general, the proximate composition of the flour depends primarily on the type of wheat. Hard wheat flours, such as hard red winter (HRW) and hard red spring (HRS) wheat, are about 82% starch, 12.5% protein, 3.5% fiber, 1.5% lipids, and 0.5% ash. These flours are preferred for bread making. PROTEINS Differences in protein content and quality among wheats affect loaf volume and the fineness, uniformity, and extensibility of the crumb grain. For bread production, good quality protein at about the 12% level is desirable.  Factors influence the protein quality 1. Wheat Type 2. Variety 3. Environmental Factors Including Nitrogen And Sulfur Availability, Heat Stress, Water Stress, And Insect Damage. 4. Storage Conditions Can Alter Protein Quality Postharvest.  Extract of protein fractions Wheat flour proteins have traditionally been sequentially extracted with salt solutions, 70% alcohol, 1% acetic acid, and reducing agents or alkali. Four fractions: albumin, globulin, gliadin, and glutenin are found.  The albumin and globulin fractions each account for about 10% of the total flour protein. Gliadin and glutenin are known as the gluten proteins; these storage proteins account for about 80% of the protein present in flour. Levels increase as total flour protein increases. The gluten proteins are responsible for dough properties.  Factors that influence bread making quality are: 1. Total amount of gluten proteins 2. Relative proportion of gliadin to glutenin present 3. The molecular weight distribution within each gluten protein fraction.  The important of flour enzymes. Lipooxygenases and amylases are often incorporated, and proteases may be added. Enzymes impact flour and dough properties, in particular dough elasticity and stickiness, gassing, and the final crumb structure in breads. It will added during either milling or bread production to enhance flour functionality. CARBOHYDRATES Starch forms the bulk of the bread dough and has several important roles in its structure. The surface of the starch granule interacts to form a strong union with gluten. Gelatinization is the process in which starch granules absorb water, swell, and break down, releasing amylose from the granule. Gelatinization of the starch, which occurs at 60–70°C (140–158°F), allows the gas-cell film to stretch.  Amylases can hydrolyze α-1,4-glycosidic linkages in carbohydrates, including starch. In flour, this activity is influenced by the degree of starch damage during the milling process. When damaged starch is hydrolyzed by amylase, absorbed water is released, making the dough softer.  Amylases, which produce maltose subsequently used in fermentation, may be present naturally or added during flour milling and/or bread production. Any residual sugar remaining post-fermentation can participate in the Maillard reaction during baking. Although wheat flour contains significant amounts of β-amylase, it is usually deficient in α- amylase.  In addition, microbial amylases, which are added by the baker or miller, have become available in recent years. Both water-soluble and water-insoluble hemicelluloses are present in wheat flour. This flour component is often referred to as pentosans because polymers of the pentose sugars D-xylose and L- arabinose dominate.  Water-insoluble pentosans 1. improve crumb uniformity 2. elasticity, 3. deleterious effects on crumb grain and texture Water-soluble pentosans 1. help regulate hydration, 2. dough development characteristics, 3. dough consistency. LIPIDS Each lipid fraction is composed of polar and nonpolar lipids, although the ratio differs among lipid fractions. 1. The polar lipids include glycolipids and phospholipids. 2. The nonpolar lipids are mainly triglycerides. Glycolipids 1. play an important role in dough development. 2. The glycolipids are bound to gliadin through hydrogen bonding and to glutenin through hydrophobic interactions in the dough OTHER ESSENTIAL BREAD INGREDIENTS 1- WATER Water is the most common liquid used in commercial baking. It comprises approximately 33–40% of the dough by weight. Water 1. responsible for hydration of the dry ingredients in the bread formula 2. forming the gluten complex during mixing. 3. serves as a dispersing medium for other ingredients, including yeast, 4. serves as a solvent for solutes (salt, sugar).  Mineral salts naturally occurring in water may affect bread dough properties. Hard waters containing high levels of calcium and magnesium ions may toughen the gluten, resulting in a tightening effect on dough. Soft waters, which lack these minerals and may be slightly acidic, may produce soft, sticky dough with impaired gas retention.  The pH of natural water is between 6 and 8; most municipal water supplies are adjusted to a pH between 7.1 & 8.5. Chilled water is often used in commercial operations to avoid excessive heat from mixing and dough development process. Temperatures above 27°C during dough development may over stimulate the yeast and adversely affect the gluten and starch. 2- YEAST The primary baker’s yeast is Saccharomyces cerevisiae. Several different strains are available. Different available forms 1. Compressed, 2. Active dry, 3. Instant. The three major functions: 1) leavening, 2) dough maturation 3) flavor development. Leavening involves the enzymatic conversion of fermentable sugars into ethanol and carbon dioxide.  Mechanism of bread production 1. sucrose is converted to glucose and fructose by invertase 2. maltose is hydrolyzed to glucose by maltase. Both invertase and maltase are yeast cell enzymes. 3- SALT Salt (sodium chloride) The three major functions in yeast-leavened breads: 1) Flavor 2) Inhibition or control of yeast activity 3) Strengthening of gluten.  In the absence of salt, the crumb of the baked loaves has an open grain and poor texture. The strengthening effect may be through direct interaction with the flour proteins. Salt’s effects on dough simulate those of oxidizing agents. OPTIONAL INGREDIENTS A. SUGAR Sucrose or corn syrup is usually incorporated in yeast- leavened breads to 1. Increase the rate of initial fermentation; 2. Amylolytic activity is required to produce a substrate for the yeast. Flavor and color effects are also found when sugar is incorporated at higher levels. In commercial yeast-bread production, liquid sugars are often used. B. FATS Desirable qualities are achieved when 2–5% fat on a flour-weight basis is incorporated. Bread volume increases by 15–25% because fat allows the dough to expand longer prior to setting. Palatability is also improved with fat incorporation into bread products. The grain is more uniform, fineness is increased, moisture perception is increased, and texture is softened. Flavor may also be enhanced. C. YEAST FOODS Yeast foods, a mixture of inorganic salts, are added for two major purposes: (1) to adjust the mineral composition of water (2) to proviTypical active ingredients 1. Yeast nutrients (ammonium salts) 2. Oxidants (usually potassium bromate or iodate), 3. pH regulators. de nitrogen and minerals for yeast. D. SURFACTANTS Surfactants (or surface-active agents) act primarily as dough conditioners and staling inhibitors. Use of surfactants in yeast-leavened breads 1. Increase in bread volume, 2. A crust and crumb that are more tender, 3. A finer and more uniform crumb cell structure, 4. Staling inhibition. D. SURFACTANTS The most commonly used surfactants 1. mono- and diglycerides, which primarily contribute softness. 2. Sodium stearoyl lactylate (SSL), another widely used surfactant, complexes with gluten proteins during gluten development, strengthening the dough.  Dough strengtheners 1. Lecithins 2. Ethoxylated monoglycerides 3. Sorbitan monosterate 4. Diacetyl tartaric esters of mono- and diglycerides. Surfactants are amphiphilic, that is, they have both hydrophilic and hydrophobic groups. Therefore, surfactants serve as a bridge between immiscible phases. E. MOLD INHIBITORS Commercial bakery products, including breads, usually contain mold inhibitors. 1. Calcium propionate, a naturally present metabolite in Swiss cheese, is most commonly used in yeast-leavened products. Typical levels are between 0.25 and 0.38% flour- weight basis in breads and rolls. 2. Sorbates may also be used as mold inhibitors. F. MILK PRODUCTS Incorporation of milk products in yeast-leavened bread can improve both its nutritional and its eating quality. Type of milk products 1. Nonfat dried milk 2. dairy blends, 3. dairy substitutes  Dairy substitutes may include 1. Soy 2. Corn flours, 3. Soy protein. Typical levels of up to 6% on a flour weight basis are used. Nonfat dried milk incorporation at the 6% level reportedly 1. increased loaf volume 2. improved texture, crust color