[推荐]卡拉胶的一点英文资料，给需要的人参考！（我看不懂） [复制链接]

谢谢,我下来看看

[此贴子已经被作者于2006-6-22 21:02:09编辑过]

是的，只是初步认识，没什么具体应用方面的，但介绍的比较全面。

如果老兄你有更好的话，还望能共享一点！

谢谢

http://bbs.tech-food.com/dispbbs.asp?BoardID=61&ID=20007&replyID=&skin=1

http://bbs.tech-food.com/dispbbs.asp?BoardID=61&ID=23297&replyID=&skin=1

Carrageenan is obtained by extraction with water or alkaline water of certain species of the class Rhodophyceae (red seaweed). It is a hydrocolloid consisting mainly of the potassium, sodium, magnesium, and calcium sulfate esters of galactose and 3.6-anhydro-galactose copolymers. The relative proportion of cations existing in carrageenan may be changed during processing to the extent that one may become predominant.

Carrageenan is recovered by alcohol precipitation, by drum drying, or by freezing. The alcohols used during recovery and purification are restricted to methanol, ethanol, and isopropanol.

The commercial products classified as carrageenan are frequently diluted with sugars for standardization purposes and mixed with food grade salts required for obtaining gelling or thickening characteristics.

The most well-known and still most important red seaweed used for manufacturing carrageenan is Chondrus crispus, which grows along the coast of the Northern part of the Atlantic, the main harvesting areas being maritime provinces of Canada, Maine, Brittany in France, and the Iberian peninsula.

Chondrus crispus is a dark red parsley-like plant which grows attached to the rocks at a depth of up to approx. 3 meters.

Most of the "moss" is harvested by rakes from small boats. The rakes may be operated by hand only or drawn after a boat.

The wet moss is brought to drying plants operated by the carrageenan manufacturers and dried to less than 20% humidity to preserve the quality of the seaweed and facilitate transportation to the extraction plant.

Other red seaweed are growing in importance as carrageenan raw materials, improving stability of supply and broadening the range of properties which can be achieved. Important species are Eucheuma cottonii, which yields kappa-carrageenan, and Eucheuma spinosum which yields iota-carrageenan. These Eucheuma species are harvested along the coasts of the Philippines and Indonesia.

Long term stability of supply and price of carrageenan raw material will be ensured by seaweed farming. Seaweed farms are already operated on the Philippines, yielding sufficient Eucheuma cottonii of good and consistent quality to cover the present demand. Eucheuma spinosum, the raw material for iota-carrageenan has recently been farmed successfully.

The advantages of seaweed farming are obvious/p>

• Independence of fluctuating climatic conditions.
• Independence of the labor intensive seaweed collecting.
• A more pure raw material.
• The possibility of selecting seaweed strains with high carrageenan content and yielding carrageenans of desired compositions and properties.

Carrageenan is extracted from the raw material with water at high temperatures. The liquid extract is purified by centrifugation and/or filtration. The liquid extract may be converted into a powder by simple evaporation of water to yield the so called drum dried carrageenan. Proper release of the dried material from the dryer roll requires addition of a small amount of roll-stripping agents (mono- and diglycerides).

The content of mono- and diglycerides is responsible for the drum dried carrageenans being turbid in watery solutions, and drum dried carrageenan consequently finds little use in water gel applications. Also, drum dried carrageenans contain all soluble salts present in the extract, which may influence the properties - for instance solubility of the carrageenan. Most of the carrageenan used in foods is isolated from the liquid extract by selective precipitation of the carrageenan with isopropanol. This process gives a more pure and concentrated product.

The flow sheet below describes in general the process used by CP Kelco ApS

Carrageenan is a linear polysaccharide, more specifically a galactan with the galactose residues linked with alternating

(13) linkages and

(14) linkages

In addition, the galactose units linked (13) in this general structure often occur as 3.6-anhydro-D-galactose and sulfate ester groups may be present on some or all galactose units.

It is evident that since carrageenan is a large molecule being made up of some 1000 residues, the possibility for structural variations are enormous. In order to simplify matters it is convenient to define three main types, kappa, iota, and lambda carrageenans, which are idealized molecules assigned definitive structures. Hardly any seaweed yields these ideal carrageenans. The normal situation is probably a range of intermediate structures.

Idealized Structures

Galactose residues in carrageenan
Kappa carrageenan is made up of

(14) D-galactose-4-sulfate and

(13) 3.6-anhydro-D-galactose.

In a kappa-type seaweed extract some of the D-galactose contains 6-sulfate ester groups and some of the 3.6-anhydro-D-galactose contains 2-sulfate ester groups.

6-sulfate ester groups reduce the gelling power considerably, but by alkali treatment it is possible to Tran eliminate 6-sulfate groups, which results in the formation of 3.6-anhydro-D-galactose imparting a higher degree of regularity to the molecule and thus the gelling power is increased.

Kappa-type extracts are made from Eucheuma cottonii and some Chondrus and Gigartina species. Iota carrageenan is characterized by having 4-sulfate ester groups on all D-galactose residues and 2-sulfate ester groups on all 3.6-anhydro-D-galactose residues. 2-sulfate ester groups are not removed by alkali treatment.

As in the case of kappa carrageenan, iota carrageenan also shows irregularities in the form of 6-sulfate ester groups on some D-galactose residues and through alkali treatment the iota carrageenan becomes more regular.

It follows that a lack of 2-sulfate ester groups on some 3.6-anhydro-D-galactose residues makes iota carrageenan more irregular. Lambda carrageenan differs from kappa and iota carrageenan by having a disulfated-D-galactose residue and no 4-sulfate in the -D-galactose residue. Instead of 4-sulfate ester groups lambda carrageenan contains variable amounts of 2-sulfate ester groups.

The position of sulfate ester groups in determined with an infrared spectrophotometer.

Typical infrared spectra are shown below/p>

Carrageenan exhibits the solubility characteristics normally shown by hydrophilic colloids. It is water soluble and insoluble in most organic solvents. Water miscible alcohols and ketones, while themselves non-solvents for carrageenan, are tolerated in admixture with carrageenan solutions at levels up to 40%. More highly polar solvents, such as formamide and N,N-dimethylformamide, are tolerated in still higher proportion and alone cause a marked swelling of the polymer.

The solubility characteristics of carrageenan in water are influenced by a number of factors most important of which are

a. the type of carrageenan
b. counter ions present
c. other solutes
d. temperature
e. pH

Type of Carrageenan

The many forms of carrageenan possible through variation in structural detail, provide much variability in regard to solubility properties. For practical purposes, however, it is convenient to speak in terms of several general structural types and to equate solubility with the overall balance of hydrophilicity as provided by the hydrophilic sulfate and hydroxyl groups on one hand and the more hydrophobic 3.6-anhydro-D-galactose residues on the other.

Thus, lambda carrageenan, by definition void of 3.6-anhydro-D-galactose units and being highly sulfated is easily soluble under most conditions. Kappa carrageenan containing 3.6-anhydro-D-galactose as part of the repeating unit and fewer sulfate groups is less hydrophilic and less soluble. Intermediate is iota carrageenan, more hydrophilic by virtue of its 2-sulfate which in addition to its position counteracts the less hydrophilic character of the 3.6-anhydro-D-galactose residue.

Counter Ions

Solubility characteristics are also affected by the salt form of the sulfated ester groups, particularly in the case of less soluble kappa carrageenan. The sodium forms are generally more easily soluble, while forms in which the cation is potassium dissolve with more difficulty.

Thus, kappa carrageenan in the potassium form may for practical purposes be considered insoluble in cold water, heat being required to bring it into solution, whereas in the sodium form it dissolves readily.

The potassium salt of iota carrageenan is also insoluble in cold water although it swells markedly. Lambda carrageenan is soluble in all its salt forms.

Other Solutes

Both the dissolving rate and solubility of carrageenan are affected by the presence of other solutes, the effect mainly being to compete for available water and thus to alter the state of hydration of the polysaccharide. Sensitivity to other solutes parallels solubility with kappa carrageenan being the most sensitive to the presence of solutes.

Inorganic salts are most effective in altering the hydration of carrageenan, particularly when the cation is potassium. 1.5 to 2% potassium chloride is sufficient to prevent the dissolution of kappa carrageenan at normal temperatures while sodium chloride solutions of 4 to 4.6% and above are also non-dissolving. Considerably higher concentrations of nonionics are required before similar effects are noted.

Sucrose shows little effect on hydration of kappa carrageenan until present in concentrations of 50% and above while glycerol must be present in very high amounts before appreciable effects are seen. In cases where more than one solute is present, their combined effect on hydration is generally additive and may be predicted from a knowledge of individual effects. For example, in the presence of high amounts of glycerol, solubility is markedly influenced by traces of potassium ions.

Of practical importance is the fact that iota carrageenan will dissolve with heating in solutions containing relatively high concentrations of salts and thus is able to provide gelation in certain applications where an excessive amount of salts would preclude the use of kappa carrageenan.

Dispersion

Being a water soluble polysaccharide, carrageenan is difficult to disperse in water due to the formation of a film layer around each carrageenan particle. This leads to the formation of large agglomerates (lumps) which, due to the protective film layer, are very difficult for the water molecules to penetrate.

The less soluble the carrageenan the easier the dispersion, for example, a potassium kappa carrageenan being insoluble in cold water is much easier to disperse in cold water than a sodium kappa carrageenan. Both, however, are soluble in hot water and therefore equally difficult to disperse in hot water. Other factors which decrease the solubility of carrageenan will improve the dispersibility.

In most applications carrageenan may be preblended with other ingredients such as sugar, and in order to achieve complete dispersion 1 part of carrageenan should be blended with 10 parts of sugar.

In applications where carrageenan cannot be preblended with other ingredients, a high speed mixer is necessary in order to break up the lumps formed by adding the carrageenan to the water.

Although potassium or calcium carrageenans are not or only slightly soluble, they swell in cold water producing viscous dispersion. Thus, dispersing carrageenan in cold water using a high speed mixer limits the strength of the dispersion to approx. 3% depending on the type of mixer.

In hot (60 - 75EC) water carrageenan can be dissolved to make 7 - 8% solution. This leads immediately to the formation of lumps, but high speed mixers are available which easily break these lumps. In hot water the carrageenan goes into true solution, and in this state the viscosity is much lower than in the state of hydration.

Stability in Solution

Acid and oxidizing agents may hydrolyze carrageenan in solution leading to loss of physical properties through cleavage of glycosidic bonds. Acid hydrolysis depends on pH, temperature and time.

For minimum degradation during processing, high temperature short time processes are preferred. Carrageenan in solution has maximum stability at pH = 9 and should not be heat processed at pH-values below 3.5. At pH = 6 or above, carrageenan solutions withstand processing conditions normally encountered by sterilizing fish and meat products in cans as in the case of pet foods.

Effect of Acid on Gel Strength of Carrageenan at 58°C 1.2% Kappa - iota carrageenan 8.0% Sugar 0.2% Potassium citrate Citric acid Effect of Acid on Gel Strength of Carrageenan at 115°C 1.0% Kappa Carrageenan - locust bean gum 1.0% Sodium chloride 0.5% Potassium chloride 0.7% Sodium citrate Citric acid buffer Effect of heat treatment on Gel Strength of Carrageenan at pH = 3.6 1.2% Kappa - iota 8.0% Sugar 0.2% Potassium citrate Citric acid

The acid hydrolysis takes place only when the carrageenan is dissolved, and the hydrolysis is accelerated as the processing temperature and/or the processing time is increased. However, when the carrageenan is in its gelled state the acid hydrolysis no longer takes place.

Reaction with other Electrically Charged Hydrocolloids

Carrageenan is a sulfated galactan being strongly negatively charged over the entire pH-range encountered in food.

Carrageenan may interact with other charged macromolecules, e.g. proteins, to give various effects such as viscosity increase, gel formation, stabilization or precipitation. The result of the carrageenan-protein interaction is highly dependent on pH of the system and the isoelectric pH of the protein. When carrageenan and gelatin are used together in a sys-tem in which the pH is higher than the isoelectric pH of gelatin, carrageenan increases the melting temperature of the gel without influencing the texture of the gel significantly.