Starch

Starch, CAS# 9005-25-8, chemical formula (C₆H₁₀O₅)_n, is a polysaccharide carbohydrate consisting of a large number of glucose monosaccharide units joined together by glycosidic bonds. All plant seeds and tubers contain starch which is predominantly present as amylose and amylopectin. Depending on the plant, starch generally contains 20 to 25 percent amylose and 75 to 80 percent amylopectin.^[1].

Etymology

Starch derived from Middle English sterchen, meaning to stiffen, which is appropriate since it can be used as a thickening agent when dissolved in water and heated. In several languages, starch is known as sago or sagu; consequently, in English sago now refers to several different starches (see Sago (disambiguation)). Starch is basically long chains of glucose molecules which all have different heights and weights

Sources of starch

Granules of wheat starch, stained with iodine, photographed through a light microscope

Starch is a white powder, and depending on the source, may be tasteless and odorless. Microscopically, starch grains are fine crystals or lumps; the precise form of these grains varies within the plant kingdom. Today, commercial starches include cornstarch, arrowroot, potato starch, sago and tapioca. Historically they included Florida arrowroot.

Uses

Starch in its basic refined form is used in cooking to thicken foods such as sauces. In industry, it is used in the manufacturing of adhesives, paper, textiles and as a mold in the manufacture of sweets such as wine gums and jelly beans. It is also used in the form of flakes, sticks, and pearls (tapioca and sago).

Food

Starch is by far the most consumed polysaccharide in the human diet. Traditional staple foods such as cereals, roots and tubers are the main source of dietary starch.

The technical term for a colorless, tasteless, odorless, and edible starch is a fecula.

Starch is often found in the fruit, seeds, rhizomes, and tubers of plants, and is the major source of energy in these food items. The major resources for starch production and consumption worldwide are rice, wheat, corn, and potatoes. Fresh chestnut has twice as much starch as potato. As the chestnut ripens, some of its starch is gradually converted into sugars.^[2] Cooked foods containing starches include boiled rice, various forms of bread and noodles (including pasta).

As an additive for food processing, arrowroot and tapioca are commonly used as well. Commonly used starches around the world are: arracacha, buckwheat, banana, barley, cassava, kudzu, oca, sago, sorghum, regular household potatoes, sweet potato, taro and yams. Edible beans, such as favas, lentils and peas, are also rich in starch.

When a starch is pre-cooked, it can then be used to thicken cold foods. This is referred to as a pregelatinized starch. Otherwise starch requires heat to thicken, or "gelatinize". The actual temperature depends on the type of starch.

A modified food starch undergoes one or more chemical modifications, which allow it to function properly under high heat and/or shear frequently encountered during food processing. Food starches are typically used as thickeners and stabilizers in foods such as puddings, custards, soups, sauces, gravies, pie fillings, and salad dressings, but have many other uses.

Resistant starch is starch that escapes digestion in the small intestine of healthy individuals.

Plants use starch as a way to store excess glucose, and thus also use starch as food during mitochondrial oxidative phosphorylation.

Starch in additives

The modified starches are coded according to the International Numbering System for Food Additives (INS) :

• 1401 Acid-treated starch
• 1402 Alkaline-treated starch
• 1403 Bleached starch
• 1404 Oxidized starch
• 1405 Starches, enzyme-treated
• 1410 Monostarch phosphate
• 1411 Distarch glycerol
• 1412 Distarch phosphate esterified with sodium trimetaphosphate
• 1413 Phosphated distarch phosphate
• 1414 Acetylated distarch phosphate
• 1420 Starch acetate esterified with acetic anhydride
• 1421 Starch acetate esterified with vinyl acetate
• 1422 Acetylated distarch adipate
• 1423 Acetylated distarch glycerol
• 1440 Hydroxypropyl starch
• 1442 Hydroxypropyl distarch phosphate
• 1443 Hydroxypropyl distarch glycerol
• 1450 Starch sodium octenyl succinate

Commercial applications

Starch adhesive

Papermaking is the largest non-food application for starches globally, consuming millions of metric tons annually. In a typical sheet of copy paper for instance, the starch content may be as high as 8%. Both chemically modified and unmodified starches are used in papermaking. In the wet part of the papermaking process, generally called the “wet-end”, starches are chemically modified to contain a cationic or positive charge bound to the starch polymer, and are utilized to associate with the anionic or negatively charged paper fibers and inorganic fillers.

These cationic starches impart the necessary strength properties for the paper web to be formed in the papermaking process (wet strength), and to provide strength to the final paper sheet (dry strength). In the dry end of the papermaking process the paper web is rewetted with a solution of starch paste that has been chemically, or enzymatically depolymerized. The starch paste solutions are applied to the paper web by means of various mechanical presses (size press). The dry end starches impart additional strength to the paper web and additionally provide water hold out or “size” for superior printing properties.

Corrugating glues are the next largest consumer of non-food starches globally. These glues are used in the production of corrugated fiberboard (sometimes called corrugated cardboard), and generally contain a mixture of chemically modified and unmodified starches that have been partially gelatinized to form an opaque paste. This paste is applied to the flute tips of the interior fluted paper to glue the fluted paper to the outside paper in the construction of cardboard boxes. This is then dried under high heat, which provides the box board strength and rigidity.

Another large non-food starch application is in the construction industry where starch is used in the gypsum wall board manufacturing process. Chemically modified or unmodified starches are added to the stucco containing primarily gypsum. Top and bottom heavyweight sheets of paper are applied to the formulation and the process is allowed to heat and cure to form the eventual rigid wall board. The starches act as a glue for the cured gypsum rock with the paper covering and also provide rigidity to the board.

Clothing starch or laundry starch is a liquid that is prepared by mixing a vegetable starch in water (earlier preparations also had to be boiled), and is used in the laundering of clothes. Starch was widely used in Europe in the 16th and 17th centuries to stiffen the wide collars and ruffs of fine linen which surrounded the necks of the well-to-do. During the 19th century and early 20th century, it was stylish to stiffen the collars and sleeves of men's shirts and the ruffles of girls' petticoats by applying starch to them as the clean clothes were being ironed. Aside from the smooth, crisp edges it gave to clothing, it served practical purposes as well. Dirt and sweat from a person's neck and wrists would stick to the starch rather than fibers of the clothing, and would easily wash away along with the starch. After each laundering, the starch would be reapplied. Today the product is sold in aerosol cans for home use.

Starch is also used to make some packing peanuts, and some dropped ceiling tiles.

Printing industry - in the printing industry food grade starch^[3] is used in the manufacture of anti-set-off spray powder used to separate printed sheets of paper to avoid wet ink being set off. Starch is also used in the manufacture of glues^[4] for book-binding.

Hydrogen production - Starch can be used to produce Hydrogen.^[5]

Oil exploration - starch is used as to adjust the viscosity of drilling fluid which is used to lubricate the drill head in (mineral) oil extraction.

Body powder - Powdered corn starch is used as a substitute for talcum powder in many health and beauty products.

Use as a mold

Gummed sweets such as jelly beans and wine gums are not manufactured using a mold in the conventional sense. A tray is filled with starch and leveled. A positive mold is then pressed into the starch leaving an impression of 1000 or so jelly beans. The mix is then poured into the impressions and then put into a stove to set. This method greatly reduces the number of molds that must be manufactured.

Starch can be modified by addition of some chemical forms to be a hard glue for paper work , some of those forms are Borax , Soda Ash , which mixed with the starch solution at 50-70C to gain a very good adhesive, Sodium Silicate can be added to reinforce this formula.

Tests

Iodine solution is used to test for starch. A bluish-black color indicates the presence of iodine in the starch solution. It is thought that the iodine fits inside the coils of amylose.^[6] A 0.3% w/w solution is the standard concentration for a dilute starch indicator solution. It is made by adding 4 grams of soluble starch to 1 litre of heated water; the solution is cooled before use (starch-iodine complex becomes unstable at temperatures above 35 °C). This complex is often used in redox titrations: in presence of an oxidizing agent the solution turns blue, in the presence of reducing agent, the blue color disappears because triiodide (I₃⁻) ions break up into three iodide ions, disassembling the complex.

Under the microscope, starch grains illuminated from behind with polarized light show a distinctive Maltese cross effect (also known as extinction cross and birefringence).

Starch derivatives

Starch can be hydrolyzed into simpler carbohydrates by acids, various enzymes, or a combination of the two. The extent of conversion is typically quantified by dextrose equivalency (DE), which is roughly the fraction of the glycoside bonds in starch that have been broken. Food products made in this way include:

• Maltodextrin, a lightly hydrolyzed (DE 10–20) starch product used as a bland-tasting filler and thickener.
• Various corn syrups (DE 30–70), viscous solutions used as sweeteners and thickeners in many kinds of processed foods.
• Dextrose (DE 100), commercial glucose, prepared by the complete hydrolysis of starch.
• High fructose syrup, made by treating dextrose solutions with the enzyme glucose isomerase, until a substantial fraction of the glucose has been converted to fructose. In the United States, high fructose corn syrup is the principal sweetener used in sweetened beverages because fructose has better handling characteristics, such as microbiological stability, and more consistent sweetness/flavor. High fructose corn syrup has the same sweetness as sugar.

See also

• Yeast extract

References