5.3.1: Bread

Bread Production

Bread is a staple food in many cultures. The key ingredients are a grain starch, water, and a leavening agent. However, there are some breads without leavening agents (tortillas or naan), but these are flat breads.

Typical Steps in Bread Production:

Leavening Organisms and Fermentation

Saccharomyces cerevisiae, also known as baker’s yeast, is the primary leavening agent in the production of most breads. Yeast cells consume the sugars present in dough and generate carbon dioxide (CO₂) and ethanol that are responsible for dough leavening during the fermentation phase and the oven rise.

Fermentable Sugars

After flour, yeast and water are mixed, complex biochemical and biophysical processes begin, catalyzed by the wheat enzymes and by the yeast. These processes go on in the baking phase. The primary starches found in most cereal plants are the polymers amylose and amylopectin.

These starches in the flour provide most of the sugar for fermentation, but the starch must be broken down into monosaccharides before it can be fermented by the yeast. Here is an overview of the sugars utilized by the yeast for the fermentation process:

Amylases: Two types of amylases are present in wheat flour: alpha-amylases and beta-amylases.

• alpha-Amylases hydrolyze the alpha-1,4 linkages inside the starch chain randomly, thereby generating shorter oligosaccharides.
• beta-Amylases cleave maltose from the non-reducing end of the starch chain.

Yeast Invertase and Maltase

• Invertase hydrolyzes several small oligosaccharides.
• Maltase cleaves maltose into the 2 monosaccharides.

 

Gluten Formation

Amongst the most important components of the flour are proteins, which often make up 10-15% of the flour. These include the classes of proteins called glutenins and gliadins. Gliadins are globular proteins with molecular weights ranging from 30,000 to 80,000 kDa. Gliadins contain intramolecular disulfide bonds.

Glutenins consist of a heterogeneous mixture of linear polymers with a large molecular weight sections and low molecular weight branches (LMW). Disulfide bond cross-link the glutenin subunits.

Prior to kneading, the two main protein types, gliadin, and glutenin, remain separate on a molecular level. However, as the dough is mixed and kneaded several things begin happening:

The protease enzymes from the wheat begin to break the glutenin into smaller pieces.

The glutenin and gliadin begin to form chemical crosslinks between the proteins. A complex network of proteins, gluten, is formed.

Starch granules are trapped in the dough and air is incorporated into the dough during kneading. The dough needs to be elastic enough to relax when it rests and expand and hold CO₂ when it rises — while still maintaining its shape. Eventually, the heat of the baking will kill the yeast.

 

Effect of Other Ingredients on Gluten Formation

• Fat and emulsifiers coat proteins.
• Salts (table salt, NaCl, or hard water salts such as Ca⁺² or Mg⁺² ) can strengthen the gluten network.

 

Cookie: Usually quite crumbly and doesn’t rise very much.

Pizza: To pull dough as thin as a pizza without breaking, there must be a very strong gluten network.

Bread: A network is tight enough to trap the yeast’s CO₂ allowing it to rise, but not so tight that it is free to expand.

 

Baking

Flavors and Aromas: Maillard Reactions

Brewer’s Journal, Science/Maillard Reaction

In food chemistry, any heating steps involving the presence of sugars and amino compounds lead to a series of reactions called the Maillard reactions. These Maillard reactions are nonenzymatic ‘browning reactions’ that lead to the formation of a wide range of flavorful compounds which include; malty, toasted, bready and nutty flavors.

There are three stages to the Maillard Reactions:

Stage I: A condensation between the sugar and amine followed by the Amadori rearrangement.
Stage II: Formation of Strecker Aldehydes
Stage III: Formation of heterocyclic nitrogen compounds.

Stage 1:

Stage 2:

Tautomerizations can convert the Amadori Product to a dicarbonyl.

In the Strecker degradation, the imine product undergoes a decarboxylation and is hydrolyzed to an aldehyde.

 

Stage 3:

In this stage, the Strecker aldehydes form complicated heterocycles in a variety of molecular families.

furanones ‘sweet, caramel’	pyrroles ‘nutty’	Acylpryidines ‘cracker’	furans ‘meaty, burnt’	thiophenes ‘meaty,roasted’
Alkylpryidines ‘bitter, burnt’	pyranones ‘maple, warm, fruity’	pyrazines ‘roasted, toasted’	oxazoles ‘nutty, sweet’	imidazoles ‘chocolate, bitter, nutty’

The molecules can also form polymers and precipitates.