Gelatin

Composition and properties

Gelatin 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 respects, closely similar to that of its parent collagen. Photographic and pharmaceutical grades of gelatin generally are sourced from beef bones and pig skin.

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 35 °C (95 °F) 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 4 °C (39 °F). The gel strength is quantified using the Bloom test.

Production

The worldwide production amount of gelatin is about 375,000–400,000 tonnes per year (830×10^⁶–880×10^⁶ lb/a). On a commercial scale, gelatin is made from by-products of the meat and leather industries. Recently, fish by-products also have been considered suitable because they eliminate some of the religious obstacles surrounding gelatin consumption. Gelatin is derived from pork skins, pork, and cattle bones, or split cattle hides. 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:

1. 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
2. The main extraction step, which usually is done with hot water or dilute acid solutions as a multistage extraction to hydrolyze collagen into gelatin
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 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.

Extraction

After 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.

Recovery

This 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 applications

The 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 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 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.

Technical uses

Dietary restrictions and gelatin substitutes

The 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, and from animals slaughtered ritually. 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 many vegetarians choose not to eat foods containing gelatin made from animals. Likewise, Hindu and Jain customs may require gelatin alternatives from sources other than animals, as many Hindus are vegetarian. Hindus who are not vegetarians often consume gelatin from all sources except cattle, which are considered sacred. 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 content

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.

Safety concerns

Since 1997, the U.S. Food and Drug Administration (FDA), with support from the TSE (transmissible spongiform encephalopathy) Advisory Committee, has been monitoring the potential risk of transmitting animal diseases, especially bovine spongiform encephalopathy (BSE), commonly known as mad cow disease. The FDA study concluded: "...steps such as heat, alkaline treatment, and filtration could be effective in reducing the level of contaminating TSE agents; however, scientific evidence is insufficient at this time to demonstrate that these treatments would effectively remove the BSE infectious agent if present in the source material."

The Scientific Steering Committee (SSC) of the European Union in 2003 stated that the risk associated with bovine bone gelatin is very low or zero. In 2006, the European Food Safety Authority (EFSA) stated that the SSC opinion was confirmed, that the BSE risk of bone-derived gelatin was very small, and removed support for the 2003 request to exclude the skull and vertebrae of bovine origin older than 12 months from the material used in gelatin manufacturing.

Today, all reputable gelatin manufacturers follow the Quality Management System according to ISO 9001. In this way, all process steps are documented. For pharmaceutical-grade gelatins, strict regulations from the FDA, the European CPMP, and European Pharmacopoeia must be met. A detailed overview of the regulatory requirements for gelatin production may be found in the Gelatine Handbook, pp. 99–101.

Health effects

In 2011, reviewing the clinical data that had been published to date, the European Food Safety Authority Panel on Dietetic Products, Nutrition, and Allergies concluded that "a cause and effect relationship has not been established between the consumption of collagen hydrolysate and maintenance of joints". A 2012 review also found insufficient evidence to support its use for osteoarthritis.

Nonetheless, in 2013, Health Canada approved a label for "hydrolyzed collagen" specifying that the label may say that it is useful to supplement dietary amino acid intake and, that it "helps to reduce joint pain associated with osteoarthritis."