Gelatin or gelatine (from meaning "stiff", "frozen") is a translucent, colorless, brittle (when dry), flavorless food derived from collagen obtained from various animal body parts. It is commonly used as a gelling agent in food, pharmaceutical drugs, vitamin capsules, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar way are called "gelatinous". Gelatin is an irreversibly hydrolyzed form of collagen, wherein the hydrolysis results in the reduction of protein fibrils into smaller peptides, which will have broad molecular weight ranges associated with physical and chemical methods of denaturation, based on the process of hydrolysis. It is found in most gummy candy, as well as other products such as marshmallows, gelatin desserts, and some ice creams, dips, and yogurts. Gelatin for recipe use 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.
Composition and propertiesGelatin is a mixture of peptides and proteins produced by partial hydrolysis of collagen extracted from the skin, bones, and connective tissues of animals such as domesticated cattle, chicken, pigs, and fish. During hydrolysis, the natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily. Its chemical composition is, in many aspects, closely similar to that of its parent collagen. Photographic and pharmaceutical grades of gelatin generally are sourced from cattle bones and pig skin. Gelatin has proline, hydroxyproline and glycine in its polypeptide chain. Glycine is responsible for close packing of the chains. Presence of proline restricts the conformation. This is important for gelation properties of gelatin. Gelatin readily dissolves in hot water and sets to a gel on cooling. When added directly to cold water, it does not dissolve well, however. Gelatin also is soluble in most polar solvents. Gelatin solutions show viscoelastic flow and streaming birefringence. Solubility 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. The mechanical properties of gelatin gels are very sensitive to temperature variations, the previous thermal history of the gels, and the amount of time elapsing. These 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, but typically, is less than and the lower limit the freezing point at which ice crystallizes. The upper melting point is below human body temperature, a factor that is important for mouthfeel of foods produced with gelatin. The viscosity of the gelatin-water mixture is greatest when the gelatin concentration is high and the mixture is kept cool at about . The gel strength is quantified using the Bloom test.
ProductionThe worldwide production amount of gelatin is about . On a commercial scale, gelatin is made from by-products of the meat and leather industries. Most gelatin is derived from pork skins, pork, and cattle bones, or split cattle hides. Fish by-products may also be used because they eliminate some of the religious obstacles surrounding gelatin consumption. The raw materials are prepared by different curing, acid, and alkali processes that are employed to extract the dried collagen hydrolysate. These processes may take several weeks, and differences in such processes have great effects on the properties of the final gelatin products. Gelatin also can be prepared in the home. Boiling certain cartilaginous cuts of meat or bones results in gelatin being dissolved into the water. Depending on the concentration, the resulting stock (when cooled) will form a jelly or gel naturally. This process is used for aspic. While many processes exist whereby collagen may be converted to gelatin, they all have several factors in common. The intermolecular and intramolecular bonds that stabilize insoluble collagen must be broken, and also, the hydrogen bonds that stabilize the collagen helix must be broken. The manufacturing processes of gelatin consists of three main stages:
- Pretreatments to make the raw materials ready for the main extraction step and to remove impurities that may have negative effects on physiochemical properties of the final gelatin product
- The main extraction step, which usually is done with hot water or dilute acid solutions as a multistage extraction to hydrolyze collagen into gelatin
- 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
PretreatmentsIf the raw material used in the production of the gelatin is derived from bones, dilute acid solutions are used to remove calcium and other salts. Hot water or several solvents may be used to reduce the fat content, which should not exceed 1% before the main extraction step. If the raw material consists of hides and skin; size reduction, washing, removal of hair from hides, and degreasing are necessary to prepare the hides and skins for the main extraction step. Collagen hydrolysis is performed by one of three different methods: acid-, alkali-, and enzymatic hydrolysis. Acid treatment is especially suitable for less fully crosslinked materials such as pig skin collagen and normally requires 10 to 48 hours. Alkali treatment is suitable for more complex collagen such as that found in bovine hides and requires more time, normally several weeks. The purpose of the alkali treatment is to destroy certain chemical crosslinks still present in collagen. Within the gelatin industry, 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. Advances are occurring to optimize the yield of gelatin using enzymatic hydrolysis of collagen. The treatment time is shorter than that required for alkali treatment, however, and results in almost complete conversion to the pure product. The physical properties of the final gelatin product are considered better.
ExtractionAfter preparation of the raw material, i.e., reducing cross-links 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 although alkali treatments speed up conversion, they also promote degradation processes. Acidic extraction conditions are extensively used in the industry, but the degree of acid varies with different processes. This extraction step is a multistage process, and the extraction temperature usually is increased in later extraction steps, which ensures minimum thermal degradation of the extracted gelatin.
RecoveryThis process includes several steps such as filtration, evaporation, drying, grinding, and sifting. These operations are concentration-dependent and also dependent on the particular gelatin used. Gelatin degradation should be avoided and minimized, so 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 gel strength, which is not generally desired.
Early history of food applicationsThe first use of gelatin in foods is attributed to Medieval Britain (1400s) when cattle hooves were boiled to produce a gel. Further commercial development occurred in 1754 when a British manufacturing patent was issued. Food applications in the USA and France during 1800–1900 appear to have established the versatility of gelatin, including the origin of its popularity in the USA as Jell-O. Over middle-late 1800s, Charles and Rose Knox of New York manufactured and marketed gelatin powder, diversifying the appeal and applications of gelatin.
Culinary usesProbably best known as a gelling agent in cooking, different types and grades of gelatin are used in a wide range of food and nonfood products: common examples of foods that contain gelatin are gelatin desserts, trifles, aspic, marshmallows, candy corn, and confections such as Peeps, gummy bears, fruit snacks, and jelly babies. Gelatin may be used as a stabilizer, thickener, or texturizer in foods such as yogurt, cream cheese, and margarine; it is used, as well, in fat-reduced foods to simulate the mouthfeel of fat and to create volume. It also is used in the production of several types of Chinese soup dumplings, specifically Shanghainese soup dumplings, or xiaolongbao, as well as Shengjian mantou, a type of fried and steamed dumpling. The fillings of both are made by combining ground pork with gelatin cubes, and in the process of cooking, the gelatin melts, creating a soupy interior with a characteristic gelatinous stickiness. Gelatin is used for the clarification of juices, such as apple juice, and of vinegar. Isinglass, from the swim bladders of fish, is still used as a fining agent for wine and beer. Besides hartshorn jelly, from deer antlers (hence the name "hartshorn"), isinglass was one of the oldest sources of gelatin.
- Certain professional and theatrical lighting equipment use color gels to change the beam color. Historically, these were made with gelatin, hence the term, color gel.
- Gelatin typically constitutes the shells of pharmaceutical capsules to make them easier to swallow. Hypromellose is a vegetarian-acceptable alternative to gelatin, but is more expensive to produce.
- Some animal glues such as hide glue may be 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, for example, it makes β-carotene water-soluble, thus imparting a yellow color to any soft drinks containing β-carotene.
- Gelatin is used as a binder in match heads and sandpaper.
- Cosmetics may contain a non-gelling variant of gelatin under the name hydrolyzed collagen.
- Gelatin was first used as an external surface sizing for paper in 1337 and continued as a dominant sizing agent of all European papers through the mid-nineteenth century. In modern times, it is mostly found in watercolor paper, and occasionally in glossy printing papers, artistic papers, and playing cards. It maintains the wrinkles in crêpe paper.
Dietary restrictions and gelatin substitutesThe consumption of gelatin from particular animals may be forbidden by religious rules or cultural taboos. For example, Jewish kosher and Islamic halal customs require gelatin from sources other than pigs, such as cattle or fish. Roma people are cautious of gelatin products that may have been made from horses, as their culture forbids the consumption of horses. Some companies specify the source of the gelatin used. Vegans and vegetarians choose not to eat foods containing gelatin made from animals. Likewise, Sikhs, Hindu and Jain customs may require gelatin alternatives from sources other than animals, as many Hindus, most Jains and some Sikhs are vegetarian. Since many people are not aware about gelatin's sources, however, they unknowingly consume it. Other people simply consider gelatin unpalatable due to the ingredients used in its production. Partial alternatives to gelatins derived from animals include the seaweed extracts agar and carrageenan, as well as pectin and konjac. Research into synthetic collagen is ongoing; as of 2011, partial success has been achieved in replicating collagen's structure using self-assembling peptides.
Protein contentcomposition]] Although gelatin is 98–99% protein by dry weight, it has little additional nutritional value, varying according to the source of the raw material and processing technique. Amino acids present in gelatin are variable, due to varying sources and batches, but are approximately:
- Glycine 21%
- Proline 12%
- Hydroxyproline 12%
- Glutamic acid 10%
- Alanine 9%
- Arginine 8%
- Aspartic acid 6%
- Other 22%