Which of the following is a carbohydrate that is commonly found in grains such as wheat, barley, and rye?: Starch and Other Complex Carbs Explained

Wheat grain is composed of approximately 70% carbohydrates by dry weight, making it a primary energy source in human diets. Which of the following is a carbohydrate that is commonly found in grains such as wheat, barley, and rye? This article delves into the composition of these important grains to provide a comprehensive answer.

Quick Summary

Starch is the primary carbohydrate in grains like wheat, barley, and rye, primarily stored for energy. Other significant components include fibrous arabinoxylans and fructans.

Key Points

• Starch is the Primary Carbohydrate: The most common carbohydrate found in grains like wheat, barley, and rye is starch, a polysaccharide composed of glucose units.

• Starch is a Complex Carbohydrate: Starch is a complex carb made of amylose and amylopectin molecules, which influence its digestion speed and glycemic index.

• Grains Contain Important Fiber: In addition to starch, grains contain non-starch polysaccharides like arabinoxylans and fructans that act as dietary fiber.

• Processing Affects Carbohydrate Content: Whole grains contain a balance of starch and fiber, while refined grains primarily consist of the starchy endosperm, which affects digestion and nutritional value.

• Fructans Can Cause Digestive Issues: Some individuals with sensitivities may experience bloating and other symptoms from fructans in grains, rather than from gluten.

The Primary Carbohydrate in Grains: Starch

Among the various options, starch is the most common and abundant carbohydrate found in grains such as wheat, barley, and rye. As a complex carbohydrate, or polysaccharide, starch is essentially a long chain of glucose units that plants produce for energy storage. In wheat, the starchy endosperm makes up about 70% of the grain's weight and consists of two main types of molecules: amylose and amylopectin.

• Amylose: This is a linear, helical molecule that constitutes about 20-30% of wheat starch. The structure of amylose makes it more difficult for digestive enzymes to break down, which contributes to what is known as 'resistant starch'. Foods containing higher levels of amylose often have a lower glycemic index, leading to a slower rise in blood sugar.
• Amylopectin: This is a much larger and more highly branched molecule than amylose, making up the remaining 70-80% of wheat starch. The branched structure allows for more surface area for digestive enzymes to act on, resulting in quicker digestion and a more rapid release of glucose.

Wheat starch is unique because it has a bimodal size distribution, containing both small and large granules, which influences its processing characteristics and texture in food products.

Other Significant Carbohydrates in Grains

While starch is the most prevalent carbohydrate, grains also contain a variety of non-starch polysaccharides, which are a type of dietary fiber crucial for digestive health.

Arabinoxylans: An Important Fiber

Arabinoxylans (AX) are the predominant non-starch polysaccharides found in the structural matrix of cell walls, particularly in the outer layers of wheat grain and bran. They are built from a backbone of xylose residues with side branches of arabinose residues. Arabinoxylans are important for several reasons:

• Water-Binding Capacity: They can bind large amounts of water, which plays a significant role in managing water content during bread-making and affects dough quality.
• Affecting Bread Quality: Water-extractable arabinoxylans (WEAX) can have a positive effect on bread quality, while water-unextractable arabinoxylans (WUAX) can have a negative impact by preventing proper hydration of gluten and starch.
• Dietary Fiber: In whole grains, arabinoxylans act as a form of dietary fiber that passes through the digestive system largely intact, adding bulk and feeding beneficial gut bacteria.

Fructans: The Prebiotic Fiber

Fructans are oligosaccharides and polysaccharides that plants use as storage carbohydrates. They consist of chains of fructose molecules that are not easily digested by humans because we lack the necessary enzymes. Instead, they are fermented by gut bacteria in the large intestine. While they act as a prebiotic fiber that supports gut health, they can also cause gastrointestinal symptoms like bloating and gas in some individuals, particularly those with irritable bowel syndrome (IBS). Fructans are found in wheat and barley, and some studies suggest that what is perceived as gluten sensitivity could, in fact, be a sensitivity to fructans.

Whole Grains vs. Refined Grains

The way a grain is processed significantly affects its carbohydrate composition and nutritional profile. The primary difference lies in which parts of the grain kernel are included.

• Whole Grains: These contain the entire kernel, including the bran, germ, and endosperm. This means they retain all the natural nutrients, including fiber, vitamins, and minerals. The fiber content, which includes arabinoxylans and fructans, slows down digestion, leading to a more gradual rise in blood sugar and promoting a feeling of fullness.
• Refined Grains: These have been milled to remove the bran and germ, leaving only the starchy endosperm. This process removes much of the dietary fiber, iron, and B vitamins. As a result, the carbohydrates are digested more quickly, which can cause a rapid spike in blood sugar.

Comparison of Carbohydrates in Grains

Feature	Starch	Arabinoxylans	Fructans
Classification	Polysaccharide	Non-starch Polysaccharide (Hemicellulose)	Oligo-/Polysaccharide
Function	Primary energy storage for plant and animal	Structural component of cell walls; dietary fiber	Storage carbohydrate; prebiotic fiber
Digestion by Humans	Primarily digestible, broken down into glucose	Indigestible; acts as dietary fiber	Indigestible; fermented by gut bacteria
Effect on Blood Sugar	Varies based on amylose/amylopectin ratio; refined grains cause spikes	Minimal direct effect due to indigestibility; slows overall digestion	Minimal direct effect; helps moderate blood sugar indirectly
Location in Grain	Endosperm (most abundant)	Bran and endosperm cell walls	Endosperm and other tissues in smaller amounts

Conclusion: More Than Just Starch

In conclusion, the answer to which of the following is a carbohydrate that is commonly found in grains such as wheat, barley, and rye? is undoubtedly starch, as it makes up the vast majority of the grain's carbohydrate content. However, a complete understanding of grain nutrition requires acknowledging the presence of other vital carbohydrates, namely arabinoxylans and fructans. These non-starchy polysaccharides function as important dietary fiber, playing distinct roles in digestive health and the physical properties of grain-based foods. The processing of grains, from whole to refined, significantly alters the ratio of these carbohydrates and their impact on our bodies. By recognizing the full spectrum of carbohydrates in grains, from the primary energy source of starch to the fibrous components, consumers can make more informed dietary choices.

For more insight into the difference between fructan and gluten sensitivities, an interesting 2017 study explored this issue, suggesting that some individuals may react to fructans rather than gluten. The study's findings are explored in more detail in a related article linked here: Fructan, not gluten, might make some sick.

Keypoints

• Starch is the Primary Carbohydrate: The most common carbohydrate in grains like wheat, barley, and rye is starch, a polysaccharide used for energy storage in plants.
• Starch Consists of Amylose and Amylopectin: Starch is comprised of two molecules: amylose (linear, slower digestion) and amylopectin (branched, faster digestion), which affect the food's glycemic index.
• Arabinoxylans are Important Dietary Fiber: These non-starch polysaccharides are a key component of grain cell walls, particularly in the bran, and play a role in digestive health.
• Fructans are Prebiotic Fibers: Grains also contain fructans, indigestible fibers that act as prebiotics for gut bacteria but can cause digestive issues for sensitive individuals.
• Whole Grains Retain All Carbs: Eating whole grains provides the full spectrum of carbohydrates, including fiber-rich bran and germ, unlike refined grains which consist mostly of the starchy endosperm.
• Carbohydrates in Grains Affect Blood Sugar Differently: The digestibility of grain carbohydrates influences blood sugar response; complex carbs like those in whole grains cause a more gradual rise than refined, starchy carbs.

FAQs

Question: Which carbohydrate is most abundant in wheat? Answer: Starch is the most abundant carbohydrate, making up the majority of the starchy endosperm in wheat grain.

Question: What other carbohydrates are in wheat besides starch? Answer: Besides starch, wheat also contains dietary fibers like arabinoxylans and fructans, which are non-starch polysaccharides.

Question: Is the carbohydrate in whole grains different from refined grains? Answer: Yes, whole grains contain the entire kernel, including fiber-rich bran and germ, while refined grains have these parts removed, leaving mostly the starchy endosperm.

Question: What are fructans and why are they a concern for some people? Answer: Fructans are prebiotic fibers in grains that can cause gas, bloating, and other digestive issues in people with conditions like irritable bowel syndrome (IBS) because they are not properly digested.

Question: Why do some people think they have gluten sensitivity when they might be sensitive to fructans? Answer: Research suggests that for some individuals, the gastrointestinal distress experienced from eating wheat may be caused by fructan malabsorption rather than an immune reaction to gluten.

Question: What role do carbohydrates in grains play in our diet? Answer: Carbohydrates from grains serve as a primary source of energy for the body and brain. Complex carbs from whole grains provide sustained energy and fiber for digestive health.

Question: How does the structure of starch affect its digestion? Answer: The structure, specifically the ratio of linear amylose to branched amylopectin, affects how quickly starch is digested. Amylose is digested slowly, while amylopectin is digested more rapidly.

Citations

• Starch - Wikipedia. (n.d.). Retrieved from https://en.wikipedia.org/wiki/Starch
• Fructans & the Low FODMAP Diet - A Little Bit Yummy. (n.d.). Retrieved from https://alittlebityummy.com/blog/fructans-the-low-fodmap-diet/
• Distribution of Arabinoxylans and Their Relationship ... - MDPI. (n.d.). Retrieved from https://www.mdpi.com/2076-3417/13/9/5458
• Understanding Wheat Starch Metabolism in Properties, ... - National Institutes of Health (NIH) | (.gov). (n.d.). Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC8624758/
• Wheat 101: Nutrition Facts and Health Effects - Healthline. (n.d.). Retrieved from https://www.healthline.com/nutrition/foods/wheat
• Types of Carbohydrates | ADA - American Diabetes Association. (n.d.). Retrieved from https://diabetes.org/food-nutrition/understanding-carbs/types-carbohydrates
• Carbohydrates: What They Are, Function & Types - Cleveland Clinic. (n.d.). Retrieved from https://my.clevelandclinic.org/health/articles/15416-carbohydrates

Frequently Asked Questions

Which carbohydrate is most abundant in wheat?

Starch is the most abundant carbohydrate in wheat, accounting for the majority of the grain's starchy endosperm.

Are there other types of carbohydrates in grains besides starch?

Yes, grains also contain dietary fibers like arabinoxylans and fructans, which are non-starch polysaccharides important for digestive health.

Is the carbohydrate in whole grains the same as in refined grains?

No, whole grains contain the entire kernel with a balance of starch and fiber. Refined grains are stripped of their bran and germ, leaving mostly the starchy endosperm.

What is the difference between amylose and amylopectin in starch?

Amylose is a linear starch molecule that digests slowly, while amylopectin is a branched molecule that is digested more quickly, affecting blood sugar response.

What are fructans and why are they a concern for some people?

Fructans are indigestible prebiotic fibers in grains that can cause gas and bloating in sensitive individuals, sometimes mistakenly attributed to gluten sensitivity.

Why are complex carbohydrates considered healthier than simple carbohydrates?

Complex carbohydrates, found in whole grains, are digested more slowly due to their fiber content, leading to a more gradual rise in blood sugar compared to simple carbs.

What is the glycemic index of grains affected by?

The glycemic index of grains is affected by the type of carbohydrate, its amylose-to-amylopectin ratio, and whether the grain is whole or refined.