Gelatin
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- For the art collective, see Gelitin.
Gelatin (also gelatine, from French gélatine) is a translucent brittle solid substance, colorless or slightly yellow, nearly tasteless and odorless, which is created by prolonged boiling of connective tissue such as skin, cartilage, and bones obtained from animal processing industry. It has been commonly used in food, pharmaceutical, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar way are called gelatinous. Gelatin is an irreversibly hydrolyzed form of collagen. Gelatin is also known as E number E441.
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[edit] Physical properties
Gelatin is a protein produced by partial hydrolysis of collagen extracted from connective tissues of animals such as porcine and bovines. The natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily. Gelatin melts when heated and solidifies when cooled again. Together with water it forms a semi-solid colloidal gel. Gelatin forms a solution of high viscosity in water, which sets to a gel on cooling and its chemical composition is, in many respects, closely similar to that of its parent collagen (1). Gelatin solutions show viscoelastic flow and streaming birefringence. If gelatin is put into contact with cold water some of the material dissolves. The solubility of the gelatin is determined by the method of manufacture. Typically, gelatin can be dispersed in a relatively concentrated acid. Such dispersions are stable for 10-15 days, with little or no chemical changes, and are suitable for coating purposes of for extrusion into a precipitating bath. Gelatin is also soluble in most polar solvents. Gelatin gels exist over only a small temperature range, the upper limit being the melting point of the gel which depends on gelatin grade and concentration and the lower limit the ice point at which ice crystallizes out. The mechanical properties are very sensitive to temperature variations, previous thermal history of the gel and time. Gelatin concentration and the temperature have important effects on viscosity, the higher they are, the higher viscosity is obtained (1).
[edit] Production
On a commercial scale, gelatin is made from by-products of the meat and leather industry, mainly pork skins, pork and cattle bones, or split cattle hides. Recently, by-products of fisheries industry began to be considered as raw material for gelatin production because of eliminating the most of the religious obstacles behind gelatin consumption (2). Contrary to popular belief, horns and hooves are not commonly used. The raw materials are prepared by different curing, acid, and alkali processes which are employed to extract the dried collagen hydrolysate, which highly affecting properties of the final gelatin product and which may take relatively long time such as several weeks (3). The worldwide production amount of gelatin is about 300,000 tons per year (roughly 600 million lbs) (4).
As for home cooking, boiling certain cartilaginous cuts of meat, or bones, will result in gelatin being dissolved into the water. Depending on the concentration, the resulting broth, when cooled, will naturally form a jelly or gel. This process may, for instance, be used for the pot-au-feu dish.
While there are many processes whereby collagen can be converted to gelatin, they all have several factors in common. The intermolecular and intramolecular bonds which stabilize insoluble collagen rendering it insoluble, must be broken and the hydrogen bonds which stabilize the collagen helix must also be broken (1). The manufacturing processes of gelatin is consisting of three main stages: 1-Pretreatments to make the raw materials ready for the main extraction step and to remove impurities which may have negative effects on technological properties of the final gelatin product, 2-The main extraction step which is usually done with hot water or dilute acid solutions as multistage extraction to hydrolyze collagen into gelatin, and finally 3-The refining and recovering treatments including filtration, clarification, evaporation, sterilization, drying, grinding, and sifting to remove the water from the gelatin solution, to blend the gelatin extracted, and to obtain dried, blended and grinded final gelatin.
[edit] Pretreatments
If the raw material which will be used in gelatin production is bones, dilute acid solutions should be used to remove calcium and similar salts. Hot water or several solvents may be used for degreasing. Maximum fat content of the material should not exceed 1% before the main extraction step. If the raw material is hides and skin, size reduction, washing, hair removing for the hides, and degreasing are the most important pretreatments used to make the hides and skins ready for the main extraction step. Raw material preparation for extraction is done by three different methods: acid, alkali, and enzymatic treatments. Acid treatment is especially suitable for less fully crosslinked materials such as pig skin. Pig skin collagen is less complex than the collagen found in bovine hides. Acid treatment is faster than alkali treatment and requires normally 10 to 48 hours. Alkali treatment is suitable for more complex collagen as being in bovine hides. This process requires longer time which takes normally several weeks. The purpose of the alkali treatment is to destroy certain chemical crosslinkages still present in collagen. The gelatin obtained from acid treated raw material has been called type-A gelatin and the alkaline treated raw material is referred to as type-B gelatin. Enzymatic treatments used for preparing raw material for the main extraction step are relatively new. Enzymatic treatments have some advantages in contrast to alkali treatment. Time required for enzymatic treatment is short, the yield is almost 100% in enzymatic treatment, the purity is also higher, and the physical properties of the final gelatin product are better.
[edit] Extraction
After preparation of the raw material, i.e., reducing crosslinkages between collagen components and removing some of the impurities such as fat and salts, partially purified collagen is converted into gelatin by extraction with either water or acid solutions at appropriate temperatures. This extraction is one of the most important steps in gelatin production. All industrially used processes are based on neutral or acid pH values because alkali treatments speeds up conversion, but, at the same time, degradation processes are promoted. Acid extract conditions are extensively used in the industry but the degree of acid varies with different processes. This extraction step is a multi stage process and extraction temperature is usually increased on later extraction steps. This procedure ensures the minimum thermal degradation of the extracted gelatin.
[edit] Recovery
This process includes several steps such as filtration, evaporation, sterilization, drying, grinding, and sifting. These operations are concentration dependent and also dependent on the particular gelatin used. Degradation must be avoided or minimized. For this purpose, limiting the temperature as much as possible would be helpful. Rapid processing is required for most of them.
[edit] Edible gelatins
Household gelatin comes in the form of sheets, granules or as powder. Instant types can be added to the food as they are; others need to be soaked in water beforehand.
Special kinds of gelatin are made only from certain animals or from fish in order to comply with Jewish kosher or Muslim halal laws. Vegetarians and vegans may substitute similar gelling agents such as agar, nature gum, carrageenan, pectin, or konnyaku sometimes referred to as "vegetable gelatins" although there is no chemical relationship; they are carbohydrates, not proteins. The name "gelatin" is colloquially applied to all types of gels and jellies, but properly used, it currently refers solely to the animal protein product. There is no vegetable source for gelatin.
[edit] Uses
Probably best known as a gelling agent in cooking, different types and grades of gelatin are used in a wide range of food and non-food products:
[edit] Food uses
Common examples of foods that contain gelatin are gelatin desserts or jelly, trifles, aspic, marshmallows and confectioneries such as Peeps, Turkish Delight and gummy bears. Gelatin may be used as a stabilizer, thickener, or texturizer in foods such as ice cream, jams, yogurt, cream cheese, margarine; it is used, as well, in fat-reduced foods to simulate the mouth feel of fat and to create volume without adding calories.
Gelatin is used for the clarification of juices, such as apple juice, and of vinegar. Isinglass, from the swim bladders of fish, is still in use as a fining agent for wine and beer. Beside hartshorn jelly, from deer antlers, isinglass was one of the oldest sources of gelatin.
[edit] Technical uses
- Gelatin typically constitutes the shells of pharmaceutical capsules in order to make their contents easier to swallow. Hypromellose is the vegetarian counterpart to gelatin, but is more expensive to produce.
- Animal glues such as hide glue are essentially unrefined gelatin.
- It is used to hold silver halide crystals in an emulsion in virtually all photographic films and photographic papers. Despite some efforts, no suitable substitutes with the stability and low cost of gelatin have been found.
- Used as a carrier, coating or separating agent for other substances, it, for example, makes beta-carotene water-soluble, thus imparting a yellow color to any soft drinks containing beta-carotene.
- Gelatin is closely related to bone glue and is used as a binder in match heads and sandpaper.
- Cosmetics may contain a non-gelling variant of gelatin under the name "hydrolyzed collagen".
- As a surface sizing it smooths glossy printing papers or playing cards and maintains the wrinkles in crepe paper.
[edit] Other uses
- Blocks of ballistic gelatin simulate muscle tissue as a standardized medium for testing firearms ammunition.
- Gelatin is used by synchronized swimmers to hold their hair in place during their routines as it will not dissolve in the cold water of the pool. It is frequently referred to as "knoxing", a reference to Knox brand gelatin. Though commonly used, the owners of the trademark object to the genericized use of the term.
- When added to boiling water and cooled, unflavored gelatin can make a home-made hair styling gel that is cheaper than many commercial hair styling products, but by comparison has a shorter shelf life (about a week) when stored in this form (usually in a refrigerator). After being applied to scalp hair, it can be removed with rinsing and some shampoo.
- It is commonly used as a biological substrate to culture adherent cells.
[edit] Medicinal and nutritional properties
Although gelatin is 98–99% protein by dry weight, it has less nutritional value than many other protein sources. Gelatin is unusually high in the non-essential amino acids glycine and proline, (i.e., those produced by the human body), while lacking certain essential amino acids (i.e., those not produced by the human body). It contains no tryptophan and is deficient in isoleucine, threonine, and methionine. The approximate amino acid composition of gelatin is: glycine 21 %, proline 12 %, hydroxyproline 12 %, glutamic acid 10 %, alanine 9 %, arginine 8%, aspartic acid 6 %, lysine 4 %, serine 4 %, leucine 3 %, valine 2 %, phenylalanine 2 %, threonine 2 %, isoleucine 1 %,hydroxylysine 1 %, methionine and histidine <1% and tyrosine < 0.5 %. These values vary, especially the minor constituents, depending on the source of the raw material and processing technique.<ref name="stevens">Stevens, P.V. (1992). "Unknown". Food Australia 44 (7): 320-324. Retrieved on 2005-08-11.</ref>
Gelatin is one of the few foods that cause a net loss of protein if eaten exclusively. Several people died of malnutrition in the 1970s while on popular 'liquid protein' diets. <ref name="FDA mag"> (April 1990) "Modified fast: A sometime solution to a weighty problem". FDA Consumer magazine: 10-17.</ref>
For decades, gelatin has been touted as a good source of protein. It has also been said to strengthen nails and hair.[[1]] [[2]] However, there is little scientific evidence to support such an assertion, one which may be traced back to Knox's revolutionary marketing techniques of the 1890s, when it was advertised that gelatin contains protein and that lack of protein causes dry, deformed nails. In fact, the human body itself produces abundant amounts of the proteins found in gelatin. Furthermore, dry nails are usually due to a lack of moisture, not protein.
Gelatin has been proven to treat ulcers. A recent study from the Institute of Molecular Genetics, Russian Academy of Sciences, Faculty of Biology of the Lomonosov Moscow State University and the Shemiakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences has shown that "gelatin peptides reinforce resistance of the stomach mucous tunic to ethanol and stress action, decreasing the ulcer area by twice."<ref>Gelatin Treats Ulcer (August 22, 2006).</ref>
Gelatin has also been claimed to promote general joint health. A study at Ball State University, sponsored by Nabisco (the former parent company of Knox gelatin[3]), found that gelatin supplementation relieved knee joint pain and stiffness in athletes. <ref name="bsu">Pearson, David. Gelatin found to reduce joint pain in athletes.</ref> These results remain yet to be replicated by other researchers.
[edit] Safety concerns
Due to Bovine spongiform encephalopathy (BSE), also known as "mad cow disease", and its link to the Creutzfeldt-Jakob disease (CJD), there has been much concern about using gelatin derived from possibly infected animal parts.<ref>Heynke, Dr. Roland. Gelatin Production and Prion Theory. -- General Information about Gelatin and Mad Cow Disease including references to various studies</ref> One study released in 2004, however, demonstrated that the gelatin production process destroys most of the BSE prions that may be present in the raw material.<ref name="grobben">Grobben, A. H., Steele, P. J.; Somerville, R. A.; Taylor, D. M. (2004). "Inactivation of the bovine-spongiform-encephalopathy (BSE) agent by the acid and alkali processes used in the manufacture of bone gelatine.". Biotechnology and Applied Biochemistry (39): 329-338.</ref> However, more detailed recent studies regarding the safety of gelatin in respect to mad cow disease have prompted the U.S. Food and Drug Administration to re-issue a warning and stricter guidelines for The Sourcing and Processing of Gelatin to Reduce the Potential Risk Posed by Bovine Spongiform Encephalopathy from 1997. Also, in 2004, the U.S. Food and Drug Administration issued a warning about testicular cancer proliferating from gelatin used in Jell-O, because of a certain method used for a short while to process the collagen through molecular reconstruction. Kraft Foods quickly altered their methods.[citation needed]
[edit] References
(1) Ward, A. G. and Courts, A. (1977) The Science and Technology of Gelatin, Academic Press, New York.
