Gelatin (spelled 'gelatine' in some Commonwealth countries from the French gélatine) is a translucent, colorless, brittle (when dry), nearly tasteless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar way are called gelatinous. Gelatin is an irreversibly hydrolysed form of collagen, and is classified as a foodstuff, with E number E441. It is found in some gummy candies as well as other products such as marshmallows, gelatin dessert, and some low-fat yogurt. Household gelatin comes in the form of sheets, granules, or powder. Instant types can be added to the food as they are; others need to be soaked in water beforehand. Some dietary or religious customs forbid the use of gelatin from certain animal sources, and medical issues may limit or prevent its consumption by certain people.
Composition and properties
Gelatin is a protein produced by partial hydrolysis of collagen extracted from the boiled bones, connective tissues, organs and some intestines of animals such as domesticated cattle, pigs, and horses. The natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily. Gelatin melts to a liquid when heated and solidifies when cooled again. Together with water, it forms a semi-solid colloid 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 or 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 freezing point at which ice crystallizes. The mechanical properties are very sensitive to temperature variations, previous thermal history of the gel, and time. The viscosity of the gelatin/water mixture increases with concentration and when kept cool (≈ 4 °C).
Production
The worldwide production amount of gelatin is about 300,000 tons per year (roughly 660 million lb).[citation needed] On a commercial scale, gelatin is made from by-products of the meat and leather industry. Recently, fish by-products have also been considered because they eliminate some of the religious obstacles surrounding gelatin consumption [2]. Gelatin is derived mainly from pork skins, pork and cattle bones, or split cattle hides; contrary to popular belief, horns and hooves are not used.[3] The raw materials are prepared by different curing, acid, and alkali processes which are employed to extract the dried collagen hydrolysate. These processes [4] may take up to several weeks, and differences in such processes have great effects on the properties of the final gelatin products [5].
Gelatin can also be prepared at your own home. 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, for instance, may 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 consists 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 physiochemical properties of the final gelatin product,
2. The main extraction step, which is usually done with hot water or dilute acid solutions as a multi-stage extraction to hydrolyze collagen into gelatin, and finally,
3. The refining and recovering treatments including filtration, clarification, evaporation, sterilization, drying, rutting, grinding, and sifting to remove the water from the gelatin solution, to blend the gelatin extracted, and to obtain dried, blended and ground final product.
Pretreatments
If the physical material that will be used in production is derived from 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, removing hair from 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 collagen. Pig skin collagen is less complex than the collagen found in bovine hides. Acid treatment is faster than alkali treatment and normally requires 10 to 48 hours. Alkali treatment is suitable for more complex collagen, e.g., the collagen found in bovine hides. This process requires longer time, 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 gelatin obtained from alkali 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.
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. All industrial processes are based on neutral or acid pH values because though alkali treatments speed up conversion, they also promote degradation processes. 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 the extraction temperature is usually increased in later extraction steps. This procedure ensures the minimum thermal degradation of the extracted gelatin.
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. Gelatin degradation should be avoided and minimized, therefore the lowest temperature possible is used for the recovery process. Most recoveries are rapid, with all of the processes being done in several stages to avoid extensive deterioration of the peptide structure. A deteriorated peptide structure would result in a low gelling strength, which is not generally desired.
Uses
more please visit http://en.wikipedia.org/wiki/Gelatin
Post
