Starch is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds.
This polysaccharide is produced by most green plants for energy storage.
Starch is a complex carbohydrate, or polysaccharide, composed of many glucose molecules joined together in a chain-like structure.
It is the primary storage form of energy in plants.
Starch serves as a reserve of glucose that can be mobilized and used when needed.
Starch is commonly found in foods derived from plant sources like grains; wheat, rice, corn, tubers; potatoes, yams; and legumes; beans, lentils.
The structure of starch can be categorized into two main forms: amylose and amylopectin.
Amylose is a linear chain of glucose molecules, while amylopectin is a branched chain with multiple side branches.
This branching allows for easier access to the glucose molecules, making amylopectin more readily metabolized and digested than amylose.
Starch is digested in the human body by enzymes called amylases.
Amylases enzymes break down the starch molecules into smaller units, such as maltose and ultimately glucose, which can be absorbed into the bloodstream and used for energy by cells.
In cooking, starch is often used as a thickening agent.
When heated in the presence of liquid, starch granules absorb water, swell, and release starch molecules that mix with the surrounding liquid.
As the mixture cools or is further heated, the starch molecules gelatinize.
This gelatinization results in the thickening of the liquid, with the desired texture of various foods like soups, sauces, gravies, and puddings.
Starch is an important dietary component providing a source of energy, particularly from carbohydrate-rich foods like grains, potatoes, and legumes.
The consumption complex carbohydrates, including starch, as part of a balanced diet for sustained energy release and to ensure an adequate intake of essential nutrients found in plant-based foods.
Refined starches, such as white bread and processed foods made with refined grains, may have lower nutritional value because they have been stripped of some beneficial components like dietary fiber and micronutrients.
Whole grains or unprocessed sources of starch can provide a higher content of fiber, vitamins, and minerals.
Starch is the most common carbohydrate in human diets, and is contained in large amounts in staple foods like wheat, potatoes, corn and rice.
Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol.
Starch consists of two types of molecules: the linear and helical amylose and the branched amylopectin.
Starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.
Glycogen, the glucose storage form is a more highly branched version of amylopectin.
Industrially, starch is converted into sugars, for example by malting, and fermented to produce ethanol in the manufacture of beer, whisky and biofuel.
Starch is processed to produce many of the sugars used in processed foods.
Mixing starches in warm water produces a paste, which can be used as a thickening, stiffening or gluing agent.
The greatest industrial non-food use of starch is as an adhesive in the papermaking process, textile goods before ironing, and to stiffen them.
Most green plants store energy as starch.
In photosynthesis, plants use light energy to produce glucose from carbon dioxide.
The glucose is used to generate the chemical energy required for general metabolism, to make organic compounds such as nucleic acids, lipids, proteins and structural polysaccharides such as cellulose, or is stored in the form of starch granules, in amyloplasts.
Fruit, seeds, rhizomes, and tubers store starch to prepare for the next growing season.
Glucose is soluble in water, hydrophilic, and binds with water.
Glucose is osmotically active.
Glucose in the form of starch, is not soluble, therefore osmotically inactive and can be stored much more compactly than glucose.
The semicrystalline granules generally consist of concentric layers of amylose and amylopectin which can be made bioavailable upon cellular demand in the plant.
Glucose molecules are bound in starch by the hydrolyzed alpha bonds.
Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the enzyme glucose-1-phosphate adenylyltransferase, and requiring energy in the form of ATP.
The enzyme starch synthase then adds the ADP-glucose via a 1,4 to a growing chain of glucose residues, liberating ADP and creating amylose.
The ADP-glucose is added to the non-reducing end of the amylose polymer, and to the non-reducing end of glycogen during glycogen synthesis.
Glycogen and amylopectin have similar structure.
Starch is synthesized in plant leaves during the day and stored as granules; it serves as an energy source at night.
The insoluble, highly branched starch chains have to be phosphorylated in order to be accessible for degrading enzymes.
After phosphorylation, the first degrading enzyme, beta-amylase (BAM) can attack the glucose chain and maltose is released as the main product of starch degradation.
The products of starch degradation are predominantly maltose and smaller amounts of glucose.
These two sugars act as a precursor for sucrose synthesis.
Sucrose can then be used in the oxidative pentose phosphate pathway in the mitochondria, to generate ATP.
Amylose is a much smaller molecule than amylopectin.
About one quarter of the mass of starch granules in plants consist of amylose, although there are about 150 times more amylose than amylopectin molecules.
Starch molecules arrange themselves in the plant in semi-crystalline granules: rice starch is relatively small (about 2 μm) while potato starches have larger granules (up to 100 μm).
Some cultivated plant varieties have pure amylopectin starch without amylose, known as waxy starches.
Waxy starches are a stable paste.
When heated in water, the granules of native starch swell and burst, and the smaller amylose molecules start leaching out of the granule, holding water and increasing the mixture’s viscosity (starch gelatinization).
During cooking, the starch becomes a paste and increases further in viscosity.
During cooling or prolonged storage of the paste, the semi-crystalline structure partially recovers and the starch paste thickens, expelling water.
This process is responsible for the hardening of bread, and for the water layer on top of a starch gel.
The enzymes that break down or hydrolyze starch into its constituent sugars are known as amylases.
Alpha-amylases are found in plants and in animals.
Saliva is rich in amylase, and the pancreas secretes the enzyme.
Individuals from populations with a high-starch diet tend to have more amylase genes than those with low-starch diets.
Beta-amylase cuts starch into maltose units and is important in the digestion of starch and is also used in brewing.
If starch is subjected to dry heat, it breaks down to form dextrins, dextrinization.
Dextrins are mainly yellow to brown in color and dextrinization is partially responsible for the browning of toasted bread.
A solution formed by mixing iodine and iodide is used to test for starch; a dark blue color indicates the presence of starch.
The strength of the resulting blue color depends on the amount of amylose present.
Each species of plant has a unique type of starch granules in granular size, shape and crystallization pattern.
Starch is the most common carbohydrate in the human diet and is contained in many staple foods.
The major sources of starch intake worldwide are the cereals, rice, wheat, and maize, and the root vegetables potatoes and cassava.
Other starchy foods: bananas, barley, breadfruit, buckwheat, canna, millet, oats, sago, sorghum, sweet potatoes, rye, taro, chestnuts, water chestnuts and yams, and many kinds of beans, such as favas, lentils, peas, and chickpeas.
Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta, porridge and tortilla.
Digestive enzymes have problems digesting crystalline structures.
Raw starch is digested poorly in the duodenum and small intestine, while bacterial degradation takes place mainly in the colon.
When starch is cooked, the digestibility is increased.
Prior to processed foods, people consumed large amounts of uncooked and unprocessed starch-containing plants, which contained high amounts of resistant starch.
Microbes within the large intestine ferment the starch, producing short-chain fatty acids, which are used as energy, and support the maintenance and growth of the microbes.
With highly processed foods, they are more easily digested and release more glucose in the small intestine.
With highly processed foods less starch reaches the large intestine and more energy is absorbed by the body, and this shift in energy delivery due to eating more processed foods may be contributing factors to the development of metabolic disorders of modern life, including obesity and diabetes.
Starch is classified as rapidly digestible, slowly digestible and resistant starch.
Raw starch granules resist digestion by enzymes and do not break down into glucose in the small intestine.
Raw starch granules reach the large intestine and function as prebiotic dietary fiber.
When starch granules are gelatinized and cooked, the starch becomes easily digestible and releases glucose quickly within the small intestine.
When starchy foods are cooked and cooled, some of the glucose chains re-crystallize and become resistant to digestion again.
Slowly digestible starch can be found in raw cereals, where digestion is slow but relatively complete within the small intestine.
Starch is extracted and refined from seeds, roots and tubers, by wet grinding, washing, sieving and drying.
The main commercial refined starches are: cornstarch, tapioca, arrowroot, wheat, rice, and potato starches.
Sources of refined starch are sweet potato, sago and mung bean.
Starch is extracted from more than 50 types of plants.
Starch can be hydrolyzed into simpler carbohydrates by acids, enzymes, or a combination of the two.
The resulting fragments are known as dextrins.
These starch sugars are by far the most common starch based food ingredient and are used as sweeteners in many drinks and foods.
They include:
Maltodextrin, a lightly hydrolyzed starch product used as a bland-tasting filler and thickener.
Various glucose syrups, also called corn syrups in the US, viscous solutions used as sweeteners and thickeners in many kinds of processed foods.
Dextrose, commercial glucose, prepared by the complete hydrolysis of starch.
High fructose syrup,
In the U.S. high-fructose corn syrup is significantly cheaper than sugar, and is the principal sweetener used in processed foods and beverages.
Fructose also has better microbiological stability.
Sugar alcohols, such as maltitol, erythritol, sorbitol, mannitol and hydrogenated starch hydrolysate, are sweeteners made by reducing sugars.
A modified starch is a starch is chemically modified to allow the starch to function properly under conditions frequently encountered during processing or storage, such as high heat, high shear, low pH, freeze/thaw and cooling.
Food starches are typically used as thickeners and stabilizers in foods: puddings, custards, soups, sauces, gravies, pie fillings, and salad dressings, and to make noodles and pastas.
Food starches function as thickeners, extenders, emulsion stabilizers and are exceptional binders in processed meats.
In the pharmaceutical industry, starch is also used as an excipient, as tablet disintegrant, and as binder.
Resistant starch is starch that escapes digestion in the small intestine of healthy individuals.
High-amylose starch from corn has a higher gelatinization temperature than other types of starch, retains its resistant starch content through baking, mild extrusion and other food processing techniques.
Resistant starch is used as an insoluble dietary fiber in processed foods such as bread, pasta, cookies, crackers, pretzels and other low moisture foods.
Resistant starch is used as a dietary supplement for its health benefits.
Published studies have shown that resistant starch helps to improve insulin sensitivity, increases satiety, reduces pro-inflammatory biomarkers interleukin 6 and tumor necrosis factor alpha and improves markers of colonic function.
It has been suggested that resistant starch contributes to the health benefits of intact whole grains.
Papermaking is the largest non-food application for starches.
In a typical sheet of copy paper for instance, the starch content may be as high as 8%.
Corrugated board adhesives are the second largest application of non-food starches.
Clothing or laundry starch is used in the laundering of clothes.
Starch is an important natural polymer used to make bioplastics.
Starch is used in the gypsum wall board manufacturing process.
Starch is used in the manufacture of various adhesives or glues for book-binding, wallpaper adhesives, paper sack production, tube winding, gummed paper, envelope adhesives, school glues and bottle labeling.
Textile chemicals from starch: yarns.
Starch is used to adjust the viscosity of drilling fluid, which is used to lubricate the drill head and suspend the grinding residue in petroleum extraction.
Starch is also used to make packing and ceiling tiles.
For body powder, powdered corn starch is used as a substitute for talcum powder, and in other health and beauty products.
Starch is used to produce various bioplastics, synthetic polymers that are biodegradable.
Glucose from starch can be further fermented to biofuel corn ethanol.
In the US the Occupational Safety and Health Administration (OSHA) has set the legal limit for starch exposure in the workplace as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday.
The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended exposure limit (REL) of 10 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday.