Collagen Type I has a globular non-collagenous part at one end of the molecule. It has no disulfide bonds. It seems that collagen is synthesized only during the formation of cartilage or inside collagen gels. We will focus on the description of collagen type I, being the largest proportion in vertebrates. Three polypeptide chains to form helices in the left direction axes is wound into a super helix sense right around a common axis. The collagen molecule is presented as a stick of 300 nm long and 15 A in diameter. It contains 1050 amino acids. The sequence repetitive proline-hydroxyproline and plays an important role in the stability of the molecule. There are carbohydrates (mono-and disaccharides units galactose-galactose and glucose) involved in the process of crosslinking.
The rigidity of the triple helix is due to hydrogen bonds formed between peptide groups, which may be involved in any way water molecules and Vander Waals hydrophobic interactions. The presence of fractions of proline and hydroxyproline, contributes to the relative thermal stability of the molecule. In the extremities of the triple helix, two amorphous parts: the telopeptides, whose chains are poor in glycine and proline, and quite rich in tyrosine. They have no helical structure. Their role is important in the maturation of collagen as it is at this level that establishes the covalent cross-links. Finally there are the N and C terminal peptides are the peptides forming the triple helix and are removed during excretion out during the synthesis of fibroblast collagen.
- Morphology: Connective tissue consists of bundles of fibers of different sizes (from microns to centimeters) according to species. Each fiber is made by the association of several fibrils. This periodic structure is explained by the management of a grid of collagen molecules. The fibrils of the lattice are displaced a quarter of its length. Degradation: Collagen is degraded under physiological conditions by specific enzymes (collagenase, neutral proteases and cathepsins lysosomals). Collagenases, main degrading enzymes are metalloenzymes that require a presence of two cofactors: calcium and zinc. Collagenase a rupture at a specific point of each chain of collagen: An N-terminal fragment (3 / 4 of the molecule). A C-terminal fragment (1 / 4 of the molecule)
The cleft involves the loss of the triple helix conformation, releasing the native chains and facilitating the attack by specific proteolytic enzymes. According to Light and Dances, the number of reducible crosslinks, decreasing over time and are replaced by stable bonds, providing chemical and physical changes (decreases solubility, susceptibility to enzymes, water retention and resistance to mechanics).
- Commercial Collagen: The commercial collagen can take many forms, solid or liquid, representing different structural states of the molecule in the connective tissues of the transformations and suffering from their extraction and preparation as feed stock. Collagen is extracted industrially from the dermis and tendons of cattle and pigs. Another source is from human placenta. Lately, it has found a protein collagen tissue of fish skeleton. They are distinguished:
- Native collagen: Collagen that has not undergone any alteration of its original structure, so it has all their polypeptide chains and their telopeptides. It may be soluble or insoluble. Native collagen-soluble neutral: it is one that can be solubilized with saline solution at neutral pH. It corresponds to the state in which the fibrillar structure is still fragile and reversible. There in a small percentage, so not removed often for industrial applications.
- Acid-soluble native collagen: is removed from contact with acidic solutions, salt precipitation and dialysis. Your source extraction are young tissues, where there is little cross-linked collagen. Native collagen insoluble in the course of aging in vivo, collagen lattice, is stabilized, leading to progressive insolubility of the fibers. This insoluble fibrous collagen is extracted from the dermis by treatment with strong organic acids.
The extraction is performed by enzymatic treatment. The enzymes break the telopeptides of the collagen molecule allowing rid the area of triple helix. The integrity of the triple helical structure is maintained and the solubility of the molecule increases. You can find 3% aqueous solutions of collagen, while there are only 0.5% maximum for soluble native collagen. Denatured collagen: There extraction methods based on the use of agents blotting, leading to a helical structure of collagen which is more or less destroyed. We are now in the appellation of Gelatin. Collagen gradient: Degradation corresponds to the breaking of the chains a. Is characterized by peptide chains of molecular weight less than 100,000. These collagens are also part of the jellies. Derived from collagen. Hydrolyzed Collagen: are aqueous solutions of lysate protein in the dermis of animals. Its average molecular weight is 1500. Collagen lyophil sate: Obtained by lyophilization of a native fibrous collagen gel. It takes the form of sheets.
- Collagen lattice: this is a polymerized collagen after suffering a process of oxidation followed by neutralization. Collagen solubility allows for variables according to their degree of crosslinking and the possibility of binding to other molecules. The term animal glue is generally applied to tails prepared from mammalian collagen, the main protein of leather, bones and tendons. Other types of glue of animal origin are designated according to the material from which they derive, for example, casein glue.
Distinction between glue and gelatin
When the insoluble protein collagen is treated with acids, alkalis or hot water, is slowly converted into a soluble material. If the original protein is pure enough and the processing is done by slow processes, the broad molecular weight product is called gelatin may be used for edible and photographic purposes. The molecular weight material produced by treating the lowest energy but less tractable sources of collagen is usually darker and is more doped. This is called animal glue. Intermediate materials can be called technical gelatin or glue of high quality. The distinction is arbitrary but is based more on the purity of the physical properties. For example, certain edible gelatins can have molecular weights lower than those of most of the queues.
Manufacture of animal glues
The chemical composition of collagen obtained from a variety of terrestrial mammals varies very little. This is equally true whether bones as part of leather. Most animal glues are made based on bones or skins of cattle. They are classified into two main types: tailbone and leather tail. The difference between the two types is mainly due to the different treatment methods. A small amount of glue is also made of leather and rabbit.
Tailbone
Bone collagen can be converted into high molecular weight gelatin after cleaning and demineralization with acids. If the bones are treated without demineralization yields a lower quality material: the tailbone.
The bones are degreased first exposing them to steam or boiling solvents such as benzene, or in more modern processes by mechanical impulses transmitted through the cold water. The cold degreasing process hurts less to collagen and makes it possible to obtain higher molecular weight products. After mechanical cleaning (polishing) the degreased bones move to autoclaves and move alternately pressurized steam and hot water for several cycles. The steam turns tail collagen and the water extracted from bones. In this way we obtain the tail as a series of dilute solutions. These can be mixed or used to extract subsequent countercurrent series. The first solutions that have been exposed to heat at least give the tails of the highest quality.
Leather Cola
Most of the leather used in the manufacture of glue and gelatin is the disposal of tannery, where he received a short treatment with saturated limewater. The pieces of leather that can lead to high quality gelatins receive further treatment with lime. After separation of the lime with water and acid, makes some extractions with rising water temperatures for a series of dilute solutions. The last of these provided technical gelatin or leather tail. Much of the queue is obtained directly from leather waste from tanneries, without subsequent treatment with lime, especially the stop scratches leather interior, called fleshing. This material should be treated with relatively high temperature water to obtain solutions of glue.
Final process. Different forms of tail
Diluted solutions of glue from bones and leather are treated equally. Usually not filtered at this stage, but may discolor and can be added preservatives. After concentrated in vacuum evaporators. Previously, it was left to solidify these concentrated solutions in the form of gelatin and cut into thick plates that are allowed to dry slowly. The glue that is sold in this way is known as Scottish tail. Today, the tail is ground to form a powder, which is much more practical use, has the great advantage of allowing the manufacturer mixing different sets of tail, so as to obtain uniform items with specific properties.
Queues can be sold also as cubes or pearls. They are results of special drying processes and for many purposes it is convenient to use them without grinding. Queues can also be directly expend tanks as hot concentrated solution from the evaporator. The queues that do not solidify in liquid form at normal temperature jelly, are made by adding chemicals that modify the properties of solidification of the ordinary animal glues. This will make products with a wide range of properties. Fish collagen tails are also obtained non-gelatinous.
Composition of animal glues
The glues and gels normally contain about 15% water and 1-4% inorganic salts. They may also contain a small amount of fat. The major high molecular weight impurity was identified as a complex mucoproteico coagulable by heat. The tail bone may contain up to 6% of this material. These impurities are not important or very little, for most uses of the tail. The properties depend on the major constituent protein derived from the breakdown of collagen. Gelatin is called the major constituent protein of jellies and colas. The purest gelatin largely consists of gelatin and water. The gelatin cannot be regarded as a simple substance, though, so we know the differences between the kinds of gelatins obtained from different sources are small.
However, the gels of the same origin can have very different physical properties as a result of differences in the production process and in particular the differences in the degree of degradation that have suffered to obtain from the original collagen. Collagen (gelatin anhydride) monomer consists of tropo-collagen fibrils arranged in interlocking networks are configured in three different peptic. The number and type of covalent bonds that develop between these chains increases with age of the animal (the lowest in younger animals). These bonds influence the molecular properties of the resulting gelatin. The conversion of trope-collagen into gelatin requires the breaking of hydrogen bonds that stabilize the helix, making it the random configuration of the gelatin.
The hydrolyzed product depends on the remaining cross-links between peptide chains and reactive groups and carboxyl terminal free amines are formed. Since all three chains are not identical, after degradation are three basic types of new channels: the alpha chains, composed of a single peptide chain, beta chain, consisting of two linked peptide chains and gamma chains with three peptide chains interconnected, hence, a sample of gelatin has several molecular weights. The molecular weight distribution of gelatin determines characteristics such as dispersibility in water, viscosity, adhesion and resistance of the gels. When the relative concentration of molecules of low molecular weight increases, viscosity decreases and the resistance of the gels. This effect is usually due to exposure of collagen and gelatin to high temperatures or high acidity or alkalinity, although it can influence the quality of raw material and alkali maceration time.
Gelatin is a protein derivative albuminoid, unlike natural gums (with which it shares some physical properties) that are polysaccharides and therefore have a completely different chemical composition. For example, agar-agar gels but also form a sulfuric acid ester with a complex array of polysaccharides obtained from an alga. Other extracts of Japanese seaweed gelatin or "isinglass" Japanese (plant agar), gum or gum Irish china. Pectin also has the capacity to form gels, but you get the fruit. Another product that is sometimes confused with gelatin rubber is explosive (blasting gelatin) which is a mixture of nitroglycerin and diatomaceous earth. It has nothing to do with animal gelatin.
From a chemical standpoint, collagen and gelatin are composed of long chains of amino acids joined by peptide bonds, amino acids containing functional groups and basic. In the amino acid composition of collagen and its derivatives, gelatin and glue, almost no concentrations of tryptophan and methionine, cystine and tyrosine are very low. For this reason, it is a complete protein from the nutritional point of view as it does the total requirements of essential amino acids (amino acids the body can not synthesize in sufficient quantities and must be supplied by the diet).
However, if the gelatin is included in a normal diet in conjunction with other proteins, may in some cases even increase the biological value of protein added? In these cases of gelatin protein combination is a good source of protein. When using a sugar substitute gelatin dessert obtained are very suitable for systems as they require more calories to be digested by the contributors themselves (ie on the specific dynamic action). Gelatin is often used as a therapeutic agent in cases of infant feeding and in patients with digestive problems, peptic ulcers, and muscular disorders and to enhance nail growth. Unlike other proteins, collagen is rich in amino acids proline and hydroxyproline. The amount of these amino acids is usually an indication of the amount of collagen in a mixture of proteins.
Raw Materials
Collagen constitutes 30% of all organic matter from the body of an animal, or 60% of total protein in the body, so it is obvious that many tissues can be used as feedstock for the manufacture of gelatin. Tissues with the highest amounts of collagen, which can be found among the products are usually the skins and bones. All other materials are used only in small quantities. Contrary to popular belief, horns, hair, feathers and egg shells can not be used to make gelatin.
Jelly Making
The objective in the development of gelatin is to control the hydrolysis of collagen (from various sources) and converting the resulting product into a soluble material with desirable physical and chemical properties, among which are the strength of the gels, adhesion, color, consistency and transparency. Essentially the process involves three basic stages:
- Separation of collagen from other components of the raw material with the least possible disruption.
- Controlled hydrolysis of collagen to gelatin conversion.
- Collection and drying of the final product.
All these steps and the starting material influences the quality and performance. Controlled hydrolysis is needed to make collagen (whose molecular weight is between 345,000 and 360,000) in gelatin (with a range of molecular weights of 10,000 to 65,000, and single and some cases reaching 250,000). however, a prolonged hydrolysis causes losses in yield and desirable properties. Also, the nature and conditions of the raw material can significantly affect the final product.
The gelatin obtained not only can vary depending on the nature of the raw material but can also vary if the products have different backgrounds and even within the same products from the same source occur daily differences of biological origin. Essentially there are three processes for gelatin from collagen with variations and combinations of procedures. The basic processes are known as alkaline, acid and steam pressure.
Alkaline procedure (gelatin type B)
The most widely used commercially is the system alkaline. Any material with collagen (skin, nerves, bone ossein) can be processed with this technique. The collagen containing material is washed well in a washing cone, a cone-shaped container that moves into a tank, a cylindrical shaker (particularly useful in the case of bones) with a rotating cylinder that raises feed stock and drops in water or a pulp wash, which consists of a semicircular tank and a rotating paddle suspended above, partially emerged in the bathroom (like the system used in the tanning industry). In the bathroom, makes the perfect raw material to soak in cold water. Then the water is replaced by a calcium hydroxide solution, prepared by dissolving lime (calcium oxide) in water. Lime is usually added in excess to maintain a saturated lime concentration throughout the long period of treatment, although an alternative procedure is to periodically renew the lime water during treatment. The amount of lime used is about 10% by weight of the raw material.
You can use any water-soluble base, but the lime is preferred because its solubility at saturation there regularly get the desired alkalinity because both collagen hydrates and other bases with the same pH value. The alkalinity makes ls substances other than collagen and keratins, globulins, mucopolysaccharides, elastin, Muscina, albumin and mucus are changed, becoming more soluble. Fats also become polar products. Thus all these products are easily removed with subsequent washing. Alkaline soaking lime also produces alterations or chemical (hydrolytic reaction) in collagen, but without any solubilization takes place appreciably, so the thermal solubilization only mission is to break such weak physical forces that maintain the structure of collagen fibrillar .
E liming procedure are released ammonia coming from the amide groups of collagen. After this process the collagen fibers are swollen and internal cohesion is reduced. This may be due to the rupture of certain peptide bonds and the introduction of new ionic groups in molecules. This is essentially a process of depolymerization in a few specific groups are broken, leading to hydrolysis of the crosslinks that hold the units of proton-collagen, collagen thus becomes a product in which only intramolecular bonds remain the basic units, so that when the propeller unfolds by heat the molecules are readily solubilized in water. There are data, which suggest that the procedure in alkaline gelatin remains slightly branched molecules with average molecular weight of 30,000 (range 10,000 to 60,000).
The duration depends on the liming material and temperature and the desired end product, but it usually takes seven days to three months, corresponding to the longest period ossein processing. The nerves require 30 - 45 days of liming; the skins of pigs require 15 to 20 days and trimmed before it is not necessary.
The skins tanned with vegetable tannins previously treated to remove tannins with a medium such as alkali borate or sodium carbonate and then extracted in the alkaline process. The remains of chromium treated hides are soaked alternately in dilute alkali and dilute acid repeatedly, or in solutions of sodium or magnesium carbonate several times to remove all the chrome. Then the skin is lime, washed and extracted in the alkaline process. You can reduce the acute period of liming the alkalinity of the brine with 0.5% sodium hydroxide or sodium carbonate 0.5%. Sometimes also added calcium chloride with 0.1% of methylamine to the brine. During the liming decreases the isoelectric point of collagen in a pH around 6.0 (day 0) to 4.8 (at 44 days), achieving the highest quality gelatin when the isoelectric point is 5.0. isoelectric point lowering with time possibly due to removal of the amide nitrogen, the formation of free carboxyl groups and the loss of other basic groups. It also depends on the period of liming the amount of gelatin to be extracted, increasing from 6% in the first day to 37% (extraction in one hour at 80 ° C) after 43 days in the lime bath.
In addition, resistance of the gels (with a 6.66% gelatin) also increases from 86 Bloom (load in grams required to produce a depression in the gel under standard conditions) on day 0 to 182 Blooms at 43 days. Also, the viscosity also increases with the period of liming. However, if the period is excessive liming can be dangerous. Sometimes completely degrade collagen so that it is not possible to collect the gelatin. The over-liming may occur when processing tissue of young animals or when the ambient temperature exceeds 30 ° C. No evidence of precision in determining the appropriate period of liming. The good results, largely still only comes from experience. Upon completion of the liming period lowers the pH and the raw material is washed with cold water to remove lime (the lime is more soluble in cold water), washed, usually lasting 1 to 2 days.
Collagen remains swollen with an alkaline reaction after washing and you have to neutralize with hydrochloric acid or dilute sulfuric acid (the acid by dissolving sulfur dioxide in water, which also whitens and preserves the product). This process continues until the collagen is deflated and loses consistency. Then wash the acid and makes a final wash with aluminum sulfate or zinc sulfate diluted. These products harden the collagen and improve the color slightly. If you are used to manufacture glue larger amounts of zinc sulphate to control bacterial growth. Such material must then have a pH between 5 and 8 (typically between 6 and 7) and is ready for extraction of collagen as gelatin.
The raw material is loaded into containers treated extraction and conduct a series of firings (usually 6 to 12, which are called first, second, third, etc.) each time at higher temperatures. Samples usually begin at 54 - 60 ° C for 3 to 5 pm and continue until the boiling point. The higher quality product (the higher strength of the gels and transparency) is obtained at lower extraction temperatures, but performance increases at higher temperatures. The most common is to get a 1 to 5% of glue or gelatin in each extraction. The residue or "crackling" is pressed, dried and sold as livestock feed or fertilizer. Each extraction is obtained and processed separately.
Liquid extracts are filtered in filter pressure steam-sterilized cellulose, to increase transparency and remove particles in suspension. It is sometimes used centrifugation for this purpose, but has the disadvantage of foam is formed easily. Gelatin solutions are difficult to filter because they clog the pores. Often, diatomaceous earth is added to facilitate the separation of small colloidal particles. Some research trials have not yet seen commercial activated carbon added to 5% and kept in solution during 4 to 6 hours at 55 - 60 ° C and then separated by centrifugation or filtration gets bleaching solutions. Another method of clarification is the addition of aluminum sulfate or a heat coagulable protein such as egg albumen, with subsequent heating to coagulate the protein (this procedure) is not used commercially). The umbrella flocculent precipitates the proteins they produce turbidity, which can then be easily removed by filtration or centrifugation.
It is usually necessary to subject the gel to a deionization if you want the ash content of less than 0.5%. This is passed the gelatin solution through a cation exchange resin box, interspersed with an anion exchange resin strong; both with large particle size, 20 - 50 mesh. The exclusion ultrafiltration membrane for molecules of less than 25,000 is also used as demineralization.
The evaporation of excess water is very critical since the temperature rise and the presence of moisture (which causes hydrolysis of peptide) reduces the quality of gelatin and an excessively long period of evaporation allows microbial growth, which also reduces the resistance of the gels. The initial extract concentration must be adequate and sufficient strength of the gels for gelled when cooled, but the successive extractions at higher temperatures usually require the application of a vacuum evaporation process for concentration to levels sufficient to gel. This is done using triple-effect evaporators or vacuum evaporators arranged after a heat exchanger, which raises the temperature of the solutions to 80 - 90 ° C. With a vacuum evaporator reaches a concentration of 11 to 17% from skin extracts from 33 - 42% in the case of bone extracts and up to 50% in lines of low quality.
The concentrated solution of gelatin is poured on a plate on which cools and solidifies (maximum of 12 mm thick), is then extracted from the plate and placed in nets (wire mesh) placed in a frame. The frames containing the gels were carried drying tunnels. The air entering these tunnels is washed, filtered and dried beforehand, making circular counter, ie in the opposite direction the trays containing gels. The air temperature rises gradually to prevent problems from peeling gels or hardening. If the air is dry, evaporation is sufficient to cool the gels and maintain the temperature below its melting point. In 8 to 12 hours will succeed in obtaining a transparent sheet brittle, with 10% humidity. The solid gelatin is sold in sheets or ground into granules of 35 - 40 mesh, although in some cases turns to dust.