Starch
| Starch | |
|---|---|
| |
| General | |
| Other names | amylum |
| Molecular formula | (C6H10O5)n |
| Molar mass | Molar mass::162.14 g/mol |
| Appearance | white powder |
| CAS number | 9005-25-8 |
| Properties | |
| Density and phase | Density::, 1.5 g/cm3 |
| Solubility in water | 50 g/L (90 C) |
| Melting point | Melting point::257°C |
| Hazards | |
| MSDS | Material safety data sheet |
| Main hazards | may cause irritation to eyes, skin, respiratory system |
| NFPA 704 |
0
0
0
|
| R/S statement | R: R20, R21, R22 S: S24, S25, S26, S27 |
| RTECS number | GM5090000 |
| Related compounds | |
| Related | amylose, amylopectin |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Disclaimer and references | |
Starch is an organic polysaccharide, that forms naturally as a means of glucose storage in plants. For years, humans have relied on the consumption of starch as a part of vital staple crops. Everything from the taste to the texture of various foods is affected by the presence of starch. It can also be used as a thickener or stiffening agent, or even be used to gel a liquid. Beyond just food and agriculture, starch has proven useful for many other applications. Adhesives, from wood glues to the glues used to hold paper sacks together are starch-based. Industries from mining and explosives to cosmetics all use starch as a primary base for many of their products.[1]
Properties
Starch is formed mainly from two molecular components: amylopectin, with a branched molecular structure, and amylose, which is typically linear or helical. Amylose has a low molecular weight , whereas amylopectin has large, though compact, molecules. Both components consist of polymers formed from α-D-glucose units. Branching points on starch depend on its source.[2] Amylopectin typically makes up the bulk of starch, composing 80-85%, while it is about 20-25% amylose. Starch is a complex carbohydrate. It is a plyomeric oligosaccharides, or polysaccharide, formed by the linkage of numerous monosaccharides. Hydroxyl groups within the compound form O-glycosidic bonds, which link the monosaccharides together. Starch molecules are semi-crystalline and tend to form in granules, especially in bio synthesis. However, the size of the granule formed usually depends on the species of plant utilizing the compound. Some can be larger or smaller depending on the particular storage needs for that plant.[3]For example, starch granules in waxy rice range anywhere from 2-13μm, whereas corn and cassava store much larger granules with a range from5-25μm, and 3-28μm respectively. Amylose content of starch in various plants varies as well. Waxy rice has no amylose but most common species of wheat contain about 26% amylose. [1]When starch is heated, it will start to lose some of its amylose molecules, and when put in a solution, can increase that solution's viscosity.[3]This owes mostly to the amylose molecules, which will reduce the crystalline nature of the structure formed by amylopectin, and allow for water to penetrate into the granules.[2]
Occurrences
Starch occurs naturally as a carbohydrate in many plants, where it functions as a glucose store. It is synthesized and stored in granules of varying sizes as an energy source for times of growth, germination, or dormancy. Most cereal grains such as rice, corn, wheat, oats, and barley, as well as tubers such as potatoes and cassava, commonly have very high concentrations of starch. Other plants include arrowroot, sago, yam and taro.[1]
Uses
The longest ongoing usage of starches by humans has been their cultivation in the staple subsistence crops of every society. Many essential food-crops, including potato, corn, cassava, arrowroot and sago all have proven valuable as easy sources of carbohydrates.
Beyond just carbohydrates starch provides many aspects and chemical characteristics of foods. This includes the viscosity of that food in colder or warmer temperatures, the speed of the canning heat transfer, freeze-thaw stability, viscosity resistance and mechanical sheer. Gel texture, clarity, opacity, tolerance of processing conditions, oil retention, resistance to gel formation, sheen and flow properties are all affected by starch. Starch provides many taste-related characteristics of foods as well, such as palate-coating, and bland tastes.
Numerous adhesives are made from starches, including hot-melt glues, stamps, bookbinding, envelopes, labels, wood adhesives, lamination, various adhesives used in the automotive industry. Starches are also used in Various fields of engineering, pressure-sensitive adhesives, adhesives used for corrugation, and the glues used to hold paper sacks together.
The explosives industry also makes frequent use of starch-based match-head binders and binding agents.
The paper industry uses starch-based products for internal sizing, surface sizing, filler retention, regular and colored paper coating, carbonless paper stilt material, and disposable papers. Arrowroot proved to be the ideal starch source for carbonless paper, as the size of the granules allowed for it function as stilt material to prevent ink capsules from rupturing. Often times, specific starch-based products require starches from specific plants, as the granule sizes vary, and one size may suit a particular job better than another. For example, larger starch granules, such as those from wheat, would prove ineffective or even useless to try to use to create carbonless paper with.
In the construction industry, many starch-based mixtures are used for binding concrete blocks, as well as binding asbestos, clay and limestone. Plywood and chipboard adhesive, as well as gypsum board binder and paint fill also all use starch-based products.
The metal and textile industries also utilize many starch-based products for foundry core binding, additives, sand casting, warp sizing, printing, and various finishes put on fabrics.
The cosmetic, pharmaceutical and mining industries rely heavily on starch-based products for the main ingredients and additives of dusting powder, make-up, soap filler and extender, facial cosmetic products, and dusting and dispersing agents. The mining industry specifically utilizes starch for ore flotation, sedimentation and various muds used in oil well drilling. Many miscellaneous uses of starches include biodegradable plastic film, dry cell batteries, printed circuit boards, and leather finishing.[1]
Starch Isolation from Biomass
Starch can be obtained from a number of plant sources such as wheat, sorghum, maize, or tubers such as potato and cassava. There are two processes for starch isolation from cereals, 'wet,' and 'dry' grind.
In the wet grind process, wheat is submerged in a mixture of water, acid and sulfur dioxide for about one to two days. Then, the grain is mashed and ground so as to remove the germ. A finer grinding process then releases the starch, gluten and fiber from the plant cells. The various materials in the resulting slurry will be separated to isolate the starch. Fiber and gluten are removed, then the mixture is dehydrated so only 40% of the moisture content remains, then dried to less than 15% moisture content. This grinding process yields not only starch, but also produces germ, gluten, protein, fiber, and fermentatives.
The dry grind process begins with having the grain milled without soaking. The starch is used immediately after milling the grain. This process is more commonly used where the quality of the starch produced is not as important, such as in grain alcohol plants. When using the dry grind process on tuber crops, they are mashed finely. The pulp is then removed, leaving a juice. Various proteins and cell debris are removed from the juice by several hydrocyclone steps. Like in the wet grind, the juice is then dehydrated to below 40% moisture content and then dried further to less than 15%[4]
References
- ↑ 1.0 1.1 1.2 1.3 Satin, Morton. Functional Properties of Starches Food and Agriculture Organization.org. Web. Accessed 28 January 2012.
- ↑ 2.0 2.1 Chaplin, Martin. Starch London South Bank Univeristy. Web. Accessed 29 January 2012.
- ↑ 3.0 3.1 Freeman, W.H.. Complex Carbohydrates National Institutes of Health. Web. 2002.
- ↑ Higson, Adrian. NNFCC Renewable Chemicals Fact sheet: Starch National Non-Food Crops Centre. May 2011.
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