Introduction
Starch and cellulose are two macromolecules that belong to the same carbohydrate family. Carbohydrates are one of the most prevalent sources of energy in foods. Their chemical formula is CH2O. These macromolecules are made up of many monomer units of glucose that are linked together chemically. They have a high molecular weight as a result.
It becomes quite interesting to know the differentiating points between the two. So, in today’s article, let’s begin with understanding the main differences and the other important details of starch and cellulose.
Starch vs Cellulose
The primary distinction between cellulose and starch is that cellulose is a structural polysaccharide with beta 1,4 connections between glucose monomers, whereas starch is a storage polymer with alpha 1,4 links. There are certain similarities as well in starch and cellulose. They include, Carbohydrates and polysaccharides are basically the same things. They consist of the same monomers: glucose. The glucose-based repeating units are the same in cellulose and starch.
Both meet our body's energy requirements. Their molecular weight is really high. The composition of cellulose and starch is very similar. Plants contain starch and cellulose.
Difference Between Starch and Cellulose in Tabular Form
| Parameters of Comparison | Starch | Cellulose |
| Definition of starch and cellulose | All repeat units in a glucose polymer are oriented in the same direction. | Cellulose is a polymer made up of glucose molecules. The subsequent glucose unit can be rotated 180 degrees around the polymer chain axis at this point. |
| The consumption | Humans can ingest starch because it is edible. | Humans are unable to consume cellulose. Only some creatures, such as cows and termites, can consume it. |
| The linkages | Alpha bonds bind units together. | Internally, Beta links connect units. |
| Water solubility | Warm water can be used to dissolve it. | Water does not dissolve it. |
| Strength | Cellulose is more powerful than starch. | Cellulose is far more powerful than starch. |
| Usage | Plants mostly use starch to store energy. | Plants mostly need cellulose to support their structure. |
| The digestion | Starch is a simple carbohydrate that is easy to digest. | Cellulose is a difficult substance to break down (Difference Between Starch and Cellulose (With Table), n.d.). |
What is Starch?
Starch that is also known as amylum, is a polymeric carbohydrate made up of several glucose units linked together by glycosidic linkages. Most green plants generate this polysaccharide to store energy. It is the most common carbohydrate in human diets worldwide, and it is abundant in staple foods like wheat, potatoes, maize (corn), rice, and cassava (manioc). Pure starch is basically a white powder that has no flavor or odor and is insoluble in cold water or alcohol. The linear and helical amylose, along with the branching amylopectin, make up this molecule. By weight, starch includes 20 to 25 percent amylose and 75 to 80 percent amylopectin, depending on the plant. Glycogen, an animal's energy reserve, is a more branched variant of amylopectin.
For example, in industry, starch is converted to sugar by malt and fermented into ethanol in the production of beer, whiskey, and biofuels. It is processed to make much of the sugar used in processed foods. Mix most starch with warm water to make the following paste. B. Wheatpaste can be used as a thickener, hardener, or adhesive. The largest non-food industry use of starch is as a paper adhesive.
The word "starch" comes from the Germanic etymology of "strong, hard, hard, hard". Modern German starch is related and has been mentioned for centuries in textiles: sizing yarn for weaving and starch linen. The Greek word for starch "Amylon", which means "unground", is also relevant. It supplies root amyl, which is used as a prefix for some 5-carbon compounds (such as amyl alcohol) that are related to or derived from starch.
The Starch Industry
In addition to the directly consumed starchy crops, in 2008, 66 million tonnes of starch were produced annually worldwide. Production in 2011 increased to 73 million tonnes.
In the EU, the starch industry produced about 11 million tonnes in 2011, of which about 40% was used for industrial purposes and 60% for food purposes. The latter was mainly used as glucose syrup. EU production in 2017 was 11 million tonnes, of which 9.4 million tonnes were consumed in the EU, 54% of which was the starch sweetener.
The energy storage
Starch, which is packed into semicrystalline granules, is used to store energy in most green plants. The excess glucose is converted to starch, which is a more complicated form of glucose than that produced by plants. Young plants rely on the energy stored in their roots, seeds, and fruits to survive until they can find adequate soil to grow in. The Asteraceae family (asters, daisies, and sunflowers) is an exception, as starch is substituted with the fructan inulin. Inulin-like fructans can also be found in wheatgrass, onions and garlic, bananas, and asparagus.
Plants use the light energy to make glucose from carbon dioxide during photosynthesis. In amyloplasts, glucose is used to generate chemical energy for general metabolism, to make organic substances like nucleic acids, lipids, proteins, and structural polysaccharides such as cellulose, or it is stored as starch granules. Starch builds up in the twigs of trees around the buds toward the end of the growing season. In order to prepare for the following growing season, fruit, seeds, rhizomes, and tubers store starch.
So basically, Glucose in the form of starch, on the contrary, is insoluble in water, is hydrophilic, binds with water, occupies a lot of space, and is osmotically active. Semicrystalline granules are made up of concentric layers of amylose and amylopectin that can be rendered bioavailable in the plant based on the cellular requirement.
The easily hydrolyzed alpha bonds bind glucose molecules in starch. The animal reserve polysaccharide glycogen contains the same type of link. Many structural polysaccharides, including chitin, cellulose, and peptidoglycan, are bonded by beta bonds and are hence far more resistant to hydrolysis.
Biosynthesis
The enzyme glucose-1-phosphate adenylyl transferase is used by plants to convert glucose 1-phosphate to ADP-glucose. This phase necessitates the use of ATP as a source of energy. The enzyme starch synthase subsequently adds the ADP-glucose to a developing chain of glucose residues via a 1,4-alpha glycosidic bond, freeing ADP and forming amylose. During glycogen production, ADP-glucose is probably certainly added to the non-reducing end of the amylose polymer, just as UDP-glucose is added to the non-reducing end of glycogen.
The starch branching enzyme creates branched amylopectin by forming 1,6-alpha glycosidic linkages between the amylose strands. Isoamylase, a starch debranching enzyme, eliminates part of these branches. There are several isoforms of these enzymes, resulting in a very complicated manufacturing process.
Glycogen and amylopectin have a similar structure, however, the former has one branch point for every ten 1,4-alpha bonds, whereas amylopectin has one branch point for every thirty 1,4-alpha bonds. Amylopectin is made from ADP-glucose, whereas mammals and fungi make glycogen from UDP-glucose; bacteria, on the other hand, make glycogen from ADP-glucose (analogous to starch).
Degradation
During the day, starch is generated in plant leaves and stored as granules; at night, it acts as an energy source. In order for degrading enzymes to access the insoluble, highly branched starch chains, they must be phosphorylated. The enzyme glucan, water dikinase (GWD) phosphorylates a glucose molecule at the C-6 position, near the 1,6-alpha branching links. Phosphoglucan, water dikinase (PWD), a second enzyme, phosphorylates the glucose molecule at the C-3 position. A lack of these enzymes, such as the GWD, results in a starch excess (sex) phenotype, and starch cannot be phosphorylated, thus it accumulates in the plastids.
Following phosphorylation, the first degrading enzyme, beta-amylase (BAM), can attack the non-reducing end of the glucose chain. The primary product of starch breakdown is maltose. BAM cannot release maltose if the glucose chain has three or fewer molecules. Disproportionating enzyme-1 (DPE1) is a second enzyme that mixes two maltotriose molecules. A glucose molecule is released from this chain. From the remaining maltose chain, BAM can now release another maltose molecule. This cycle continues until all of the starch has been destroyed. BAM can't release maltose if it gets too close to the phosphorylated branching point of the glucose chain. The enzyme isoamylase (ISA) is necessary for the degradation of the phosphorylated chain.
The products of starch degradation are predominantly maltose and smaller amounts of glucose. These molecules are then exported from the plastid to the cytosol, maltose via the maltose transporter, which if mutated (MEX1-mutant) results in maltose accumulation in the plastid. Glucose is exported through the plastidic glucose translocator (pGlcT). These two sugars then act as a precursor for sucrose synthesis. After that, Sucrose can be used in the oxidative pentose phosphate pathway in the mitochondria, to generate ATP at night (Starch, n.d.).
What is Cellulose?
Anselme Payen, a French scientist, discovered cellulose in 1838 after isolating it from plant matter and determining its chemical formula. Hyatt Manufacturing Company employed cellulose to create the first viable thermoplastic polymer, celluloid, in 1870. Cellophane was created in 1912, while rayon ("fake silk") was first produced from cellulose in the 1890s. In 1920, Hermann Staudinger discovered the polymer structure of cellulose. Kobayashi and Shoda were the first to chemically synthesize the molecule (without the assistance of any biologically derived enzymes) in 1992.
cellulose is also much more crystalline than starch. When heated beyond 60–70 °C in water (as in cooking), starch transforms from crystalline to amorphous, but cellulose requires a temperature of 320 °C and a pressure of 25 MPa to become amorphous in water.
Types
There are several varieties of cellulose. The placement of hydrogen bonding between and within the strands distinguishes these types. Natural cellulose has structures I and I and is classified as cellulose I. Bacteria and algae create cellulose that is high in me, whereas higher plants produce cellulose that is mostly I. Cellulose II is the type of cellulose found in regenerated cellulose fibers. Because cellulose I to cellulose II conversion is irreversible, cellulose I am metastable and cellulose II is stable. The structures cellulose III and cellulose IV can be produced through a variety of chemical treatments.
Properties
Many of cellulose's qualities are influenced by its chain length or degree of polymerization, which refers to the number of glucose units in each polymer molecule. Wood pulp cellulose has a chain length of 300 to 1700 units, while cotton and other plant fibers, as well as bacterial cellulose, have a chain length of 800 to 10,000 units. Cellodextrins are cellulose-derived molecules with very short chain lengths that are soluble in water and organic solvents, unlike long-chain cellulose.
(C6H10O5)n is the chemical formula for cellulose, with n denoting the degree of polymerization and n denoting the number of glucose groups.
Plant-derived cellulose is typically mixed with hemicellulose, lignin, pectin, and other compounds, whereas bacterial cellulose is nearly pure, has significantly higher water content, and has a much better tensile strength due to longer chain lengths.
Fibrils of cellulose have crystalline and amorphous areas. Mechanical treatment of cellulose pulp, typically aided by chemical oxidation or enzymatic treatment, can produce semi-flexible cellulose nanofibrils ranging in size from 200 nm to 1 m in length, depending on the treatment intensity. Cellulose pulp can also be treated with a strong acid to hydrolyze the amorphous fibril regions, resulting in short stiff cellulose nanocrystals with a length of a few hundred nanometers. Due to their self-assembly into cholesteric liquid crystals, formation of hydrogels or aerogels, application in nanocomposites with superior thermal and mechanical properties, and use as Pickering stabilizers for emulsions, these nano celluloses are of significant technological importance (Cellulose, n.d.).
Main Differences Between Starch and Cellulose In Points
- So, A glucose polymer in which all repeat units are oriented in the same direction is known as starch.
- Cellulose is a glucose polymer in which each glucose unit may spin around the backbone polymer chain's axis.
- Alpha bonds link the units together in starch.
- Internally, beta chains link these units together in cellulose.
- Because we have enzymes that can break down starch into glucose, it is edible.
- Humans are unable to digest cellulose because it is inedible (Difference Between Starch and Cellulose (With Table), n.d.).
Conclusion
Thus, now we came to know the key differentiating points between starch and cellulose. We got to learn some other knowledgeable facts as well.
References
- Cellulose. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Cellulose
- Starch. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Starch
