Starch is a carbohydrate that, upon digestion, is converted into glucose and obtained from plants such as potatoes, wheat, corn, etc.
Starch is the energy stored by the plants that are long chains of polysaccharides, the sugar molecules linked together. Therefore, starch is comprised of glucose, a sugar molecule. This complex carbohydrate is found in all plants and therefore exists in several foods such as vegetables, grains, and fruits. Starch contains two main polysaccharides: amylose and amylopectin. Amylopectin is a branched polysaccharide and is therefore easily digested and absorbed compared to amylose, which is a linear polysaccharide. Since starch is converted to glucose, consequently increased amount of carbohydrate consumption can lead to a spike in blood sugar levels, cholesterol, insulin, and an increase in body fat. However, foods containing an increased amount of amylose are observed to have increased resistant starch that is not entirely digested and hence is not absorbed by the body. Thus, they have decreased fat storage and low cholesterol levels. Furthermore, starch is utilized in different biomaterials in various industries.
Overview of Starch
Starch is a soft, white granular, tasteless compound produced by plants. It is insoluble in cold water and other solvents such as alcohol. Starch is a carbohydrate polysaccharide containing glucose monomers such as amylose (linear polymer in simple form) and amylopectin (branched structure). Polysaccharides are long chains of monosaccharides linked together. A monosaccharide is a single sugar molecule. Hence, when these sugar molecules link together to form a polysaccharide. Therefore, amylose and amylopectin are polysaccharides. Starch comprises a sugar molecule called glucose, composed of carbon, hydrogen, and oxygen. The chemical formula of starch is C6H12O6.
The plants utilize glucose to generate energy; however, the remainder of the energy is stored as starch. Humans digest starch with the help of the amylase enzyme in the saliva and small intestine converting it into maltose, limiting dextrins and glucose derivatives. They are then digested in the small intestine into monosaccharides like glucose, fructose, and galactose. When the glucose in blood level rises, through glycogenesis, excess glucose is converted to glycogen in the liver for temporary storage.
The simplest starch is amylose (by Meyer in 1940), a polysaccharide consisting of multiple monomers of glucose chained by 1,4 alpha linkages linearly and is used as a biomaterial in industries. Alpha- glycosidic bonds link the glucose monomers. The IUPAC name of amylose is (1-4)-alpha-D-Glucopyranan, and the chemical formula is represented as (C6H10O5)n. Amylose is primarily used in industrial manufacturing in plastics, paper pulp fiber bonding, and textiles. Amylose starches have also been used as food gums to function as a binder that provides crispiness to french fries and helps absorb less oil. This type of starch is also used in food wrapping casings to heat the food uniformly in a microwave. Amylose is mainly found in most starchy food and vegetables, rice, potatoes, legumes, whole grains, and beans. Amylose is a water-soluble (insoluble in cold water) compound that covers 20-25% of starch.
Amylopectin (C30H52O26) is a complex form of starch, which is quite similar to that of amylose, except that amylopectin is branched while amylose is linear chains. Since the amylopectin is branched, they have a higher molecular weight than the amylose. Amylopectin is composed mainly of (1-4)-alpha-D-Glucopyranan units with (1-6)-alpha linkages between them. This compound belongs to carbohydrates, which are stored as temporary granules in plants and broken down by enzymes later into glucose. Glucose is required for the production of energy in plants and animals. Since amylopectin is a complex starch, it can be broken down quickly due to its higher glycemic index (a measure of blood sugar level in carbohydrate-containing food). This can lead to an increase in blood sugar levels immediately after eating. Foods containing high amylopectin are white bread, white potatoes, cookies, cornflakes, puffed rice, etc.
Health Benefits and Risks
Consumption of a limited amount of carbohydrate-containing food will help maintain the average blood glucose level. Amylopectin is a branched molecule rapidly digested to glucose and absorbed by the body. This leads to rising blood sugar levels and insulin levels immediately after consuming amylopectin-content food. Insulin is a hormone produced in the liver responsible for transporting glucose from the blood to different cells to convert it into energy for the cells to function. An increase in insulin in the long term will reduce insulin’s effectiveness, causing resistance and increasing blood-sugar levels.
Indigestible carbohydrate (fiber) is an integral part of a nutritious diet. Carbohydrates that are not digested are dietary fibers only present in plant-based foods, such as potatoes, corn, beets, fruits, beans, and whole grains. Soluble fiber absorbs water that provides nutrition for the good bacteria in the gut, aids in slow digestion, and softens the stool. Insoluble fiber that does not absorb water passes into the digestive system into the rectum to accumulate the mass initiating bowel movements and avoiding constipation. The soluble fiber is obtained majorly from fruits and vegetables. Leafy green vegetables, nuts, seeds, and whole-grain foods are good sources of insoluble fiber.
Consumption of an increased amount of food containing high amylopectin has increased blood cholesterol levels by decreasing triglycerides and good HDL cholesterol levels. Insulin resistance is found to be correlated with the increase in the production of cholesterol when compared to a diet containing amylose. Since insulin plays an essential role in the metabolism and storage of fat, insulin resistance will increase fat storage, thereby reducing fat burning and causing increased belly fat when food containing amylopectin is consumed.
Commercially, starch, mainly from corn with wheat potato and tapioca, is utilized for industrial purposes. Starch is obtained from crushing seeds or tubers containing starch; the pulp is mixed with water. After removing impurities, the paste is dried and converted into a powdered form. Starch is a thickening agent like corn starch for baking and confections. Starch is also used to manufacture paper to increase paper strength and sizing.
Starches obtained from plants are chemically modified to produce physical changes to bring about appearance, shelf stability, and food preparation. Few modified starches are cross-linked (in pizza sauce), pregelatinized (pudding mixes), stabilized (frozen foods), cold water-swelling (salad dressings), and acid-modified starches (like gelatin). Furthermore, starch is also utilized to manufacture paper bags, gummed paper, and tapes.