What Polysaccharides Are Found in Bread?

Bread, a staple food for many cultures, contains a rich and complex array of polysaccharides, with starch being the most abundant. These complex carbohydrates, which are large molecules made from many sugar units, are derived from the cereal grains used to make flour and are fundamentally responsible for bread's structure, texture, and nutritional value. During the baking process, these polysaccharides undergo critical transformations that shape the final product we consume.

Quick Summary

The polysaccharides in bread encompass both digestible starches and various types of dietary fiber. Starch, composed of amylose and amylopectin, forms the core structure, while non-starch polysaccharides like arabinoxylans, β-glucans, and cellulose contribute to fiber content and influence dough properties. During baking, dextrins form and resistant starch develops, altering the final texture and digestibility of the bread.

Key Points

• Starch Dominates: The primary polysaccharide in bread is starch, composed of both linear amylose and branched amylopectin, which dictates the crumb's structure.

• Dietary Fiber is Key: Whole-grain breads are rich in non-starch polysaccharides (NSPs), including arabinoxylans, β-glucans, and cellulose, which provide dietary fiber.

• Arabinoxylans Enhance Dough: Arabinoxylans (AX) influence water absorption and viscosity, helping to form the dough structure and improve gas retention.

• Baking Creates Dextrins and Resistant Starch: The heat from baking causes dextrinization, browning the crust and creating dextrins. As bread cools, some starch retrogrades to form resistant starch (RS3).

• β-Glucans Offer Health Benefits: Particularly found in oat and barley flour, β-glucans are a soluble fiber known for lowering cholesterol and regulating blood sugar.

• Different Flours, Different Polysaccharides: The specific profile of polysaccharides, and thus the properties of the bread, varies significantly depending on the type of cereal grain used.

• Water Management is Crucial: Both starch and certain NSPs have a high water-binding capacity, making water management a key factor in achieving optimal dough consistency and final bread quality.

The Polysaccharide Foundation of Bread: Starch

At the heart of bread's composition is starch, the primary carbohydrate stored in cereal grains like wheat, rye, and barley. Starch itself is a polysaccharide, a long chain of glucose units linked together, but it exists in two primary forms with different structures and functions.

Amylose and Amylopectin: The Starch Duo

Starch granules contain a mixture of two glucose polymers: amylose and amylopectin. The ratio of these two components significantly affects the properties of flour and the resulting bread.

• Amylose: This is a linear, helical chain of glucose molecules. Flours with higher amylose content tend to produce harder, more resistant starches. Upon cooking and cooling, amylose can re-associate, a process known as retrogradation, which contributes to bread staling.
• Amylopectin: This is a highly branched molecule of glucose units. Amylopectin makes up the majority of most starches (75-80%) and plays a critical role in the gelatinization of starch during baking, which sets the bread's crumb structure.

Starch Transformation During Baking

When bread dough is baked, the starch granules absorb water and swell, a process called gelatinization. As the temperature increases, the gelatinized starch forms a gel that helps set the final structure of the bread. The heat also triggers dextrinization, a reaction that breaks down some starches into smaller, sweeter dextrin molecules, contributing to the browning and flavor of the crust.

The Role of Non-Starch Polysaccharides (NSPs)

Beyond starch, bread contains a variety of non-starch polysaccharides (NSPs), which are a major component of dietary fiber. These are particularly abundant in whole-grain breads, as many are found in the bran and aleurone layers of the grain.

Arabinoxylans: Critical for Dough Properties

Arabinoxylans (AX) are the primary NSPs in wheat and rye flour, and they are composed of a xylan backbone with arabinose residues. They are critical to breadmaking for several reasons:

• Water Absorption: Both water-soluble and water-insoluble arabinoxylans have a high capacity to bind water, which influences dough consistency and yield.
• Dough Properties: Water-soluble arabinoxylans can increase the viscosity of dough and interact with gluten proteins to form a complex network. This affects the dough's strength and gas retention during fermentation.

β-Glucans: The Heart-Healthy Fiber

β-Glucans are another important NSP, particularly in oats and barley, and to a lesser extent in wheat. They are long, linear chains of glucose units that are not digestible by human enzymes. β-glucans are known for their health benefits, such as lowering cholesterol and regulating blood sugar. In baking, they form viscous solutions that can impact dough hydration and bread texture.

Cellulose: Insoluble and Structural

Cellulose, the most abundant organic polymer on Earth, is also present in bread, especially whole-grain varieties. It is a linear polysaccharide of glucose units that is completely insoluble and indigestible for humans. Cellulose primarily provides structure to the plant cell walls and is a key component of insoluble fiber in bread.

The Polysaccharide Story During Baking and Beyond

Dextrinization: The Science of the Crust

As heat transforms dough into bread, dextrinization occurs on the surface. This process breaks down some of the starch into smaller dextrin molecules, which contributes to the brown coloration and distinct crispness of the crust.

Resistant Starch: A Fiber-Like Effect

During the cooling process, some starches in the baked bread, especially those cooked and then cooled (like in day-old bread), form resistant starch (RS3). This type of starch is resistant to digestion and functions similarly to dietary fiber, feeding beneficial gut bacteria. The crust of bread can also contain resistant starch (RS2) that never fully gelatinized.

Comparative Table: Polysaccharides in Bread

Polysaccharide	Type of Bread	Location in Grain	Functional Role	Health Benefit
Starch	Most types	Endosperm	Provides structure, energy source for yeast and body	Major energy source
Amylose	All types	Endosperm	Contributes to starch retrogradation (staling)	Can form resistant starch (RS3) after cooking/cooling
Amylopectin	All types	Endosperm	Gelatinizes to form bread's crumb structure	Digested for energy
Arabinoxylan	Whole-grain (especially rye)	Cell walls (bran, endosperm)	Water absorption, dough viscosity, interacts with gluten	Soluble fiber, may feed beneficial bacteria
β-Glucan	Whole-grain (especially oat, barley)	Cell walls (endosperm)	Water absorption, influences dough viscosity	Soluble fiber, lowers cholesterol, regulates blood glucose
Cellulose	Whole-grain	Cell walls (bran)	Insoluble structural component	Insoluble fiber, aids digestion
Dextrin	Crust of most types	Surface (formed during baking)	Browning, crust flavor, crispness	Digestible, though some are not fully broken down
Resistant Starch	Day-old/cooled bread	Re-crystallized starch	Resists digestion	Supports gut health, blood sugar control

Conclusion

The polysaccharides found in bread are far more than just a source of calories. From the major starch components of amylose and amylopectin, which dictate the bread's fundamental structure, to the vital non-starch polysaccharides like arabinoxylans and β-glucans that contribute dietary fiber, each plays a unique and essential role. The transformations that occur during mixing, fermentation, and baking, such as gelatinization, retrogradation, and dextrinization, highlight the complex chemical science behind a seemingly simple food. Understanding this intricate network of polysaccharides offers a deeper appreciation for the culinary art of baking and its nutritional impact. For further reading, an excellent resource on the properties and functionality of cereal non-starch polysaccharides in breadmaking is published by MDPI.

References

Bieniek, A., & Buksa, K. (2023). Properties and Functionality of Cereal Non-Starch Polysaccharides in Breadmaking. Applied Sciences, 13(4), 2282. MDPI.

Final Thoughts

While we often focus on protein (gluten) in bread, it is the remarkable diversity and chemical nature of the flour's polysaccharides that truly shape the final loaf. These carbohydrates control water dynamics, gas retention, flavor, and texture, influencing everything from crust crispness to crumb softness and even a bread's health benefits. By appreciating the nuanced roles of each polysaccharide, we can understand how different flours and baking methods produce a vast array of unique and delicious breads.

Frequently Asked Questions

What is the most abundant polysaccharide in bread?

The most abundant polysaccharide in bread is starch, which makes up the majority of the dry weight of flour. It is a polymer of glucose and is composed of both linear amylose and branched amylopectin molecules.

How do polysaccharides affect the texture of bread?

Polysaccharides dramatically affect bread texture. Starch, for instance, gelatinizes during baking to set the crumb structure. Non-starch polysaccharides like arabinoxylans and β-glucans bind water and influence dough viscosity, affecting the crumb's softness and overall mouthfeel.

Does bread contain dietary fiber?

Yes, bread contains dietary fiber, especially whole-grain varieties. This fiber is made up of non-starch polysaccharides, such as arabinoxylans, β-glucans, and cellulose, which are mainly found in the bran and aleurone layers of the grain.

What is the difference between starch and non-starch polysaccharides in bread?

Starch is a digestible polysaccharide that serves as a primary energy source. Non-starch polysaccharides, which constitute dietary fiber, are not digestible by human enzymes. They play structural roles in the flour and offer different health benefits.

What are dextrins and how are they formed in bread?

Dextrins are smaller carbohydrate chains formed from the breakdown of starch during the dry heat of baking, a process called dextrinization. They contribute to the golden-brown color, crispness, and flavor of the bread crust.

What is resistant starch and how does it get into bread?

Resistant starch (RS3) is a type of starch that forms when gelatinized starch cools and retrogrades, becoming resistant to digestion. The cooling of baked bread creates this resistant starch, which behaves like dietary fiber and supports gut health.

Why is whole-grain bread healthier in terms of polysaccharides?

Whole-grain bread is generally considered healthier because it contains a much higher concentration of non-starch polysaccharides and total dietary fiber, particularly from the bran and germ. This leads to increased nutrient intake and benefits for digestive and cardiovascular health.