The food we eat plays a critical role in how our bodies function. Food With Polysaccharides It is often a primary source of dietary energy, so it needs to be digested and metabolized. Polysaccharides are generally water-soluble carbohydrates that are not easily absorbed by the human GI tract. However, they do have many health benefits including acting as prebiotics and promoting intestinal health, aiding in digestion by acting as fiber or bulking agents, improving nutrient absorption while also maintaining blood glucose levels and immunity; increasing satiety (feeling full) while reducing appetite; decreasing fat storage and caloric consumption; reducing blood pressure; promoting heart health; lowering cholesterol.
Food With Polysaccharides
Carbohydrates can be divided into several categories: monosaccharides, disaccharides and polysaccharides. Chemically speaking, the prefix before “saccharides” indicates how many saccharide chains are attached to the molecule. Polysaccharides have many chains and must be broken down into smaller portions before they can be fully digested. Although polysaccharides are a form of sugar, many of their food sources rarely taste sweet.
potatoes are a “starchy carbohydrate”
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One example of a polysaccharide found in foods is starch. This is the main carbohydrate source for plant seeds and tubers, or vegetables that grow in the ground. Starch food sources often are referred to as “starchy carbohydrates” and include foods like corn, potatoes and rice. Other examples include bread, cereal and pasta. These foods are the most common form of carbohydrates in your diet, comprising an estimated one-third of the foods you eat. The body breaks starches down into glucose, which helps to give you energy.
cellulose can be found in apple skin
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Cellulose is another polysaccharide commonly found in foods. Cellulose provides a protective covering and/or structure to fruits and vegetables and their seeds. It gives foods a crunchy texture and is undigestible in the body. However, cellulose does act as a source of dietary fiber, adding bulk to your stool and helping to maintain regular digestive processes. Many fruits and vegetables contain some aspect of cellulose, including in the skins of apples and pears, in the covering of whole grains like wheat bran and in plant leaves like spinach. Seeds and nuts also contain cellulose.
carrots are a source of soluble fiber
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Pectin is a compound that helps to form a gel-like substance when broken down in the body. Food sources that contain pectin also are known as soluble fiber sources. Soluble fiber is beneficial to the body because it prolongs stomach emptying, helping you to feel fuller, longer. Examples of soluble fiber include oats, dried beans, nuts, barley, flax seed, oranges, apples, carrots and psyllium husk.
olive oil is a healthier choice for food preparation
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Although starchy foods can get a bad reputation for being high-fat food sources, they contain fewer than half the calories of fats in your diet. They also are sources of fiber, calcium, iron and vitamins in your daily diet. To keep dietary polysaccharides as healthy options for you, cook your foods in healthy oils like olive or vegetable oils and avoid high-fat preparation methods like frying foods because such methods can offset the nutritional value of these foods.
What Foods Contain Polysaccharides?
Polysaccharides are complex macromolecules essential for many bodily functions found in a wide variety of carbohydrate-based food sources. The four monosaccharides, often referred to as simple sugars, of fructose, glucose, lactose, and galactose, can join together to produce a polysaccharide. When glucose and fructose are joined together, they produce sucrose, or table sugar, one of several common disaccharides. Other types of polysaccharides include starch, glycogen, and xanthan gum in plants. Starches are known as storage polysaccharides because they contain glucose, which is the most easily broken down sugar for energy, and is concentrated in all grains, potatoes, beans, and more.
Glycogen is one of the main polysaccharides that is similar in structure to starches, and is considered the primary energy storage molecule in animals, as well as lower life forms, such as yeast and fungi. Glucose is a core component of the glycogen molecule, and it is released from glycogen through a process of hydrolysis, or chemical decomposition in water. When foods are said to have a glycemic index, it is this ability of a glycogen-based food molecule to release glucose into the bloodstream for energy. Foods with glucose as their primary form of sugar have the highest glycemic index, and these include processed wheat grains, dates, and white bread.
Foods such as bananas and potato chips can have a different glycemic index than their molecular structure would suggest. This is because certain factors slow down the breaking up of carbohydrates to release glucose. Sugars, such as fructose in bananas or lactose in dairy products, are more slowly digested than glucose-based foods. A food like potatoes with a high glycemic index that is processed into potato chips will also slow down digestion, as fat added to the chips inhibits the breakdown of glucose from the potato starch. Unprocessed starch and foods with a lot of fiber can be hard for the body to digest as well, so brown rice would be broken down more slowly than rice cereal, and raw beans slower than cooked beans.
Since polysaccharides themselves are insoluble in water, they can store glucose as an energy molecule without affecting the cells they are in until needed. This is why consuming large amounts of carbohydrates can contribute to weight gain. There is nothing essentially wrong with carbohydrates, but they are polysaccharide molecules designed as an efficient way to store energy in stable form for both plants and animals. Their ability to hold energy in the form of glycogen in animals and as cellulose in plants is the same as storing calories, and excess calorie consumption is the root cause of weight gain.
Carbohydrates are a major source of food and an important form of energy for most living organisms. A carbohydrate is a biomolecule consisting of carbon, hydrogen, and oxygen atoms. The two basic compounds that makeup carbohydrates are – Aldehydes and Ketones.
Carbohydrates are found in all-natural and processed foods. The three types of carbohydrate are:
- Monosaccharides– Glucose and galactose are examples of monosaccharides.
- Disaccharides–Sucrose and maltose are examples of disaccharides.
- Polysaccharides– Starch, glycogen, and cellulose are examples of polysaccharides.
Here, in this article, let us explore in further detail about the Polysaccharides, its types, properties and its functions.
What are Polysaccharides?
Polysaccharides are major classes of biomolecules. They are long chains of carbohydrate molecules, composed of several smaller monosaccharides. These complex bio-macromolecules functions as an important source of energy in animal cell and form a structural component of a plant cell. It can be a homopolysaccharide or a heteropolysaccharide depending upon the type of the monosaccharides.
Polysaccharides can be a straight chain of monosaccharides known as linear polysaccharides, or it can be branched known as a branched polysaccharide.
Characteristics Of Polysaccharides
Polysaccharides have the following properties:
- They are not sweet in taste.
- Many are insoluble in water.
- They are hydrophobic in nature.
- They do not form crystals on desiccation.
- Can be extracted to form a white powder.
- They are high molecular weight carbohydrates.
- Inside the cells, they are compact and osmotically inactive.
- They consist of hydrogen, carbon, and oxygen. The hydrogen to oxygen ratio being 2:1.
Types Of Polysaccharides
Polysaccharides are categorized into two types:
A polysaccharide that contains the same type of monosaccharides is known as a homopolysaccharide. Some of the important homopolysaccharides are:
- Glycogen: It is made up of a large chain of molecules. It is found in animals and fungi.
- Cellulose: The cell wall of the plants is made up of cellulose. It comprises long chains of ꞵ-glycosides.
- Starch: It is formed by the condensation of amylose and amylopectin. It is found largely in plants, fruits, seeds, etc.
- Inulin: It is made up of a number of fructofuranose molecules linked together in chains. It is found in the tubers of dahlia, artichoke, etc.
A polysaccharide that contains different types of monosaccharides is known as a heteropolysaccharide. Some of the important heteropolysaccharides are:
- Hyaluronic Acid: It is made up of D-glucuronic acid and N-acetyl-glucosamine. It is found in connective tissues and skin.
- Heparin: It is made up of D-glucuronic acid, L-iduronic acid, N-sulfo-D-glucosamine and is largely distributed in mast cells and blood.
- Chondroitin-4-sulfate: Its component sugars are D-glucuronic acid and N-acetyl-D-galactosamine-4-O-sulfate. It is present in the cartilages.
- Gamma globulin: N-acetyl-hexosamine, D-mannose, D-galactose are the component sugars of this polysaccharide. It is found in the blood.
Functions Of Polysaccharides
The polysaccharides serve as a structural organization in animals and plants. Other functions of polysaccharides include:
- They store energy in organisms.
- Due to the presence of multiple hydrogen bonds, the water cannot invade the molecules making them hydrophobic.
- They allow for changes in the concentration gradient which influences the uptake of nutrients and water by the cells.
- Many polysaccharides become covalently bonded with lipids and proteins to form glycolipids and glycoproteins. These glycolipids and glycoproteins are used to send messages or signals between and within the cells.
- They provide support to the cells. The cell wall of plants is made up of polysaccharide cellulose, which provides support to the cell wall of the plant. In insects and fungi, chitin plays an important role in providing support to the extracellular matrix around the cells.
Types of Carbohydrates
On this page, we’ll get acquainted with the chemical structure of different types of carbohydrates and learn where we find them in foods.
First, all carbohydrates are made up of the same chemical elements:
- carbon (that’s the “carbo-” part)
- hydrogen and oxygen, in about a two-to-one proportion, just like in H2O (that’s the “-hydrate” part)
For this reason, you may see carbohydrates abbreviated as “CHO” in our class.
Carbohydrates can be divided into two main types: simple and complex. Simple carbohydrates are made up of just one or two sugar units, whereas complex carbohydrates are made up of many sugar units. We’ll look at each of these in turn. This figure gives you an overview of the types of carbohydrates that we’ll cover.
Fig. 2.1. Carbohydrates can be divided into two main types: simple (including monosaccharides and disaccharides) and complex.
Simple carbohydrates are sometimes called “sugars” or “simple sugars.” There are 2 types of simple carbohydrates: monosaccharides and disaccharides.
Monosaccharides contain just one sugar unit, so they’re the smallest of the carbohydrates. (The prefix “mono-” means “one.”) The small size of monosaccharides gives them a special role in digestion and metabolism. Food carbohydrates have to be broken down to monosaccharides before they can be absorbed in the gastrointestinal tract, and they also circulate in blood in monosaccharide form.
There are 3 monosaccharides:
Note that all three have the same chemical formula (C6H22O6); the atoms are just arranged a bit differently.
1 – Glucose
Here’s the chemical structure of glucose:
You’re already familiar with glucose, because it’s the main product of photosynthesis. Plants make glucose as a way of storing the sun’s energy in a form that it can use for growth and reproduction.
In humans, glucose is one of the most important nutrients for fueling the body. It’s especially important for the brain and nervous system, which aren’t very good at using other fuel sources. Muscles, on the other hand, can use fat as an energy source. (In practice, your muscles are usually using some combination of fat and glucose for energy, which we’ll learn more about later.)
Food sources of glucose: Glucose is found in fruits and vegetables, as well as honey, corn syrup, and high fructose corn syrup. (All plants make glucose, but much of the glucose is used to make starch, fiber, and other nutrients. The foods listed here have glucose in its monosaccharide form.)
2 – Fructose
Here’s the chemical structure of fructose:
Fructose is special because it is the sweetest carbohydrate. Plants make a lot of fructose as a way of attracting insects and animals, which help plants to reproduce. For example, plants make nectar, which is high in fructose and very sweet, to attract insects that will pollinate it. Plants also put fructose into fruit to make it tastier. Animals eat the fruit, wander away, and later poop out the seeds from the fruit, thereby sowing the seeds of the next generation. Animal gets a meal, and the plant gets to reproduce: win-win!
Fig. 2.2. Fructose in nature: A bee collects sweet nectar from a flower, in the process spreading pollen from flower to flower and helping plants to reproduce. Bees use nectar to make honey, which humans harvest for use as a sweetener. (Honey contains a mix of sucrose, fructose, and glucose). A kiwi is sweetened in part by fructose. Animals enjoy the sweet fruit and then later poop out the seeds, sowing them for a new generation of kiwi trees.
Food sources of fructose: Fruits, vegetables, honey, high fructose corn syrup
3 – Galactose
Here is the chemical structure of galactose:
Food sources of galactose: Galactose is found in milk (and dairy products made from milk), but it’s almost always linked to glucose to form a disaccharide (more on that in a minute). We rarely find it in our food supply in monosaccharide form.
The second type of simple carbohydrates is disaccharides. They contain two sugar units bonded together.
There are 3 disaccharides:
- Maltose (glucose + glucose)
- Sucrose (glucose + fructose)
- Lactose (glucose + galactose)
1 – Maltose
Maltose is made of two glucose molecules bonded together. It doesn’t occur naturally in any appreciable amount in foods, with one exception: sprouted grains. Grains contain a lot of starch, which is made of long chains of glucose (more on this in a minute), and when the seed of a grain starts to sprout, it begins to break down that starch, creating maltose. If bread is made from those sprouted grains, that bread will have some maltose. Sprouted grain bread is usually a little heavier and sweeter than bread made from regular flour.
Maltose also plays a role in the production of beer and liquor, because this process involves the fermentation of grains or other carbohydrate sources. Maltose is formed during the breakdown of those carbohydrates, but there is very little remaining once the fermentation process is complete.
You can taste the sweetness of maltose if you hold a starchy food in your mouth for a minute or so. Try this with a simple food like a soda cracker. Starch is not sweet, but as the starch in the cracker begins to break down with the action of salivary amylase, maltose will form, and you’ll taste the sweetness!
2 – Sucrose
Sucrose is made of a glucose molecule bonded to a fructose molecule. It’s made by plants for the same reason as fructose — to attract animals to eat it and thereby spread the seeds.
Sucrose is naturally-occurring in fruits and vegetables. (Most fruits and vegetables contain a mixture of glucose, fructose, and sucrose.) But humans have also figured out how to concentrate the sucrose in plants (usually sugar cane or sugar beets) to make refined table sugar. We also find sucrose in maple syrup and honey.
The sucrose found in sweet potato is chemically identical to the sucrose found in table sugar. Likewise, the fructose found in a fig is chemically identical to the fructose found in high fructose corn syrup. As we’ll discuss more later, what’s different is the package the sugars come in. When you eat a sweet potato or a fig, you also get lots of fiber, vitamins, and minerals in that package, whereas sugar and high fructose corn syrup only provide sugar, nothing else. It’s not a bad thing to eat sugar. After all, it’s a vital fuel for our brain and nervous system. But paying attention to the package it comes in can help us make good overall choices for health.
3 – Lactose
Lactose is made of a glucose molecule bonded to a galactose molecule. It is sometimes called “milk sugar” as it is found in dairy products like milk, yogurt, and cheese. These are the only animal foods that have significant amounts of carbohydrate. Most of our carbohydrates come from plant foods.
Complex carbohydrates are also called polysaccharides, because they contain many sugars. (The prefix “poly-” means “many.”) There are 3 main polysaccharides:
All three of these polysaccharides are made up of many glucose molecules bonded together, but they differ in their structure and the type of bonds.
1 – Starch
Starch is made up of long chains of glucose. If these chains are straight, they’re called amylose; if they’re branched, they’re called amylopectin.
Here is an amylose segment containing 3 glucose units.
The next figure shows an amylopectin segment containing 4 glucose units. The chemical structure is represented differently, but can you spot the place where it branches?
Using our green hexagon to represent glucose, you can picture starch as something like this:
Humans have digestive enzymes to break down both types of starch, which we’ll discuss on the next page.
Starch is the storage form of carbohydrate in plants. Plants make starch in order to store glucose. For example, starch is in seeds to give the seedling energy to sprout, and we eat those seeds in the form of grains, legumes (soybeans, lentils, pinto and kidney beans, for example), nuts, and seeds. Starch is also stored in roots and tubers to provide stored energy for the plant to grow and reproduce, and we eat these in the form of potatoes, sweet potatoes, carrots, beets, and turnips.
When we eat plant foods with starch, we can break it down into glucose to provide fuel for our body’s cells. In addition, starch from whole plant foods comes packaged with other valuable nutrients. We also find refined starch – such as corn starch – as an ingredient in many processed foods, because it serves as a good thickener.
2 – Glycogen
Glycogen is structurally similar to amylopectin, but it’s the storage form of carbohydrate in animals, humans included. It’s made up of highly branched chains of glucose, and it’s stored in the liver and skeletal muscle. The branched structure of glycogen makes it easier to break down quickly to release glucose to serve as fuel when needed on short notice.
Liver glycogen is broken down to glucose, which is released into the bloodstream and can be used by cells around the body. Muscle glycogen provides energy only for muscle, to fuel activity. That can come in handy if you’re being chased by a lion, or sprinting to make your bus!
Even though glycogen is stored in the liver and muscles of animals, we don’t find it in meat, because it’s broken down soon after slaughter. Thus, glycogen is not found in our food. Instead, we have to make it in our liver and muscle from glucose.
Here’s a beautiful depiction of glycogen.
Fig. 2.3 – Glycogen is made from long, branching chains of glucose, radiating around a central protein.
3 – Fiber
Fiber includes carbohydrates and other structural substances in plants that are indigestible to human enzymes. Fiber is made by plants to provide protection and structural support. Think about thick stems that help a plant stand upright, tough seed husks, and fruit skin that protect what’s growing inside. These are full of fiber.
Fig. 2.4 – Examples of food plants high in fiber, including wheat, broccoli, and apples.
In our food, we find fiber in whole plant foods like whole grains, seeds, nuts, fruits, vegetables, and legumes.
One of the most common types of fiber is cellulose, the main component in plant cell walls. The chemical structure of cellulose is shown in the figure below, with our simplified depiction next to it. You can see that cellulose has long chains of glucose, similar to starch, but they’re stacked up, and there are hydrogen bonds linking the stacks.
When we eat fiber, it passes through the small intestine intact, because we don’t have digestive enzymes to break it down. Then, in the large intestine, our friendly microbiota — the bacteria that live in our colons — go to work on the fiber. Some fiber can be fermented by those bacteria. We’ll discuss fiber more later in the unit.