What are the applications of alginate in the food industry?

Alginic acid and alginates are polysaccharides mainly extracted from brown algae (Phaeophyceae) of the genus Lamiaria hyperborea, L. digitata, and Ecklonia maxima, Macrocystis pyrifera, Ascophyllum nodosum, Fucus serratus and other species of seaweeds. Ascophyllum nodosum, Fucus serratus and other species of seaweeds. Alginic acid and alginate is a main product of seaweed industry in China. According to its nature, it can be mainly divided into water-soluble gum and insoluble gum two categories. Water-soluble alginate includes monovalent salt of alginate (sodium, potassium, ammonium alginate, etc.), two divalent salts of alginate (magnesium alginate and mercury alginate) and alginate derivatives; water-insoluble seaweed gum includes alginate, divalent salts of alginate (except magnesium and mercury salts) and trivalent salts of alginate (aluminum alginate, iron, chromium, etc.). The most widely used of these are sodium alginate, calcium alginate and propylene glycol alginate.

 

This type of alginate is found in the cell walls of seaweeds, and in its natural state it is a mixture of insoluble alginate (calcium, magnesium, sodium, potassium) salts. When extracted commercially, it is first treated with acid to convert it into insoluble alginate, then treated with alkali to form a soluble alginate solution, and then through a number of processes such as purification and filtration, it can be obtained through the addition of different substances to obtain different commercial alginate gum. Alginate is obtained through acid treatment, calcium alginate is obtained through CaCl2/CaCO3 treatment, sodium alginate is produced through Na2CO3 treatment, and ammonium alginate is produced through neutralization with carbonic acid. Alginate is reacted with propylene oxide to produce another important chemically modified derivative of alginate, propylene glycol alginate (PGA). Alginate is widely used in the food and pharmaceutical industries because of its unique gel properties and its ability to thicken, stabilize, emulsify, disperse and form films.

 

Picture I. Chemical composition and structure of alginate

 

Seaweed gum or alginate is the main polysaccharide structural component of brown seaweed. Alginate polymer consists of two monomers: β(1→4)-D-mannuronic acid unit and α(1→4)-L-guluronic acid unit, these two monomers alternately combine with each other to become three different structural chain segments, which are as follows: chain segment composed of mannuronic acid (-M-M-M-M-); chain segment composed of guluronic acid (-G-G-G-G-); and chain segment composed of two monomers alternately (M-G-M-M-G); a chain segment composed of guluronic acid (-G-G-G-G-); and a chain segment composed of two alternating monomers (M-G-M-G). The polymer molecule of seaweed gum consists of these three chain segments. The molecular weight can be as high as 200,000 molecules. The ratio of monomers to chain segments varies and depends on the raw material of the alginate. Different sources contain different ratios of mannuronic acid (M) to guluronic acid (G), resulting in different uses and properties. In a molecule, it may contain a continuous chain segment made up of only one of the glyoxylates, or it may be a block copolymer made up of two glyoxylate links. Variations in the proportions of the two glucuronic acids in the molecule, as well as differences in their location, can lead directly to differences in the properties of alginate, such as viscosity, gelling properties, and ion selectivity.

 

The polyguluronic acid chain segments are more rigid than the polymannuronic acid chain segments and have a larger nematic volume in solution, while the chain segments consisting of different kinds of glycoaldehydic acid links have better flexibility and a smaller nematic volume in solution than those consisting of the two glycoaldehydic acids mentioned above alone. All other things being equal, the greater the rigidity of the chain segments of the alginate molecule, the greater the viscosity of the solution prepared and the greater the brittleness of the gel formed．

 

Each kind of seaweed contains its different structure of seaweed gel, the special structure of seaweed gel has a great influence on its properties, especially on the presence of calcium ions when the gelling effect. The polyguluronic acid chain segments bind very strongly to calcium ions and form a fully polymerized reticular structure. The polymannuronic acid chain segments, while also binding to calcium, are not as strong. The calcium ion binds preferentially to the guluronic acid and also binds well to the guluronic acid residues between the two different chain segments. Complex binding between many chain segments on different molecules together form a complete mesh structure and form a gel. High molecular weight, low calcium content or high glucuronic acid composition of the chain segments of the seaweed gum formed a hard gel, has good gelling properties, generally used in food as a gelling agent. On the contrary, alginate gum with low molecular weight, high calcium content or containing chain segments composed of high mannuronic acid is often used as a thickener in food.

 

Chemical derivatives of alginic acid

 

Alginic acid can be made into a number of derivatives through the later chemical modification process. Propylene glycol alginate (PGA) is one of the most typical derivatives, but also has realized the industrial production and a large number of alginate derivatives have been applied.PGA has acid stability, and can prevent the precipitation caused by calcium and other high-valent metal ions, which has obvious advantages in the application of some acidic food.

 

In addition, alginate can be reacted with organic amines to produce ammonium alginate salts. Organic amines that can be used include: triethanolamine, triisopropylamine, butylamine, dibutylamine and dipentylamine. Ammonium alginate can also be produced by reacting PGA with primary amines such as ammonia, ethanolamine, ethylenediamine, ethylamine, propylamine, isobutylamine and butylamine, but it is not easy to react with secondary amines. Industrial production of ammonium alginate is generally produced by neutralizing alginic acid with ammonia or ammonium carbonate. At present, although it has been able to synthesize alginate acetate and alginate sulfate, but it has not yet been applied in practice. Carboxymethyl alginate can be made by treating sodium alginate with chloroacetic acid and alkali, and a series of hydrocarbon-based diol esters of alginate can also be synthesized. Ethylene oxide and alginate reaction can generate 2-hydroxyethyl alginate.

 

Third, the physical properties of alginate

 

Commercially useful water-soluble seaweeds include monovalent salts of alginate (sodium alginate, potassium alginate, ammonium alginate), calcium alginate, ammonium-calcium mixed salts of alginate, alginic acid, and propylene glycol ester of alginate.

 

Alginate, as a hydrophilic polysaccharide substance, readily absorbs water from the atmosphere and thus the equilibrium moisture content is related to the relative humidity. Alginate has good dry storage stability at room temperature or lower, so alginate products should be stored in a cool, dry place.

 

Alginate is a kind of hydrophilic polymer, when it is put into the water, if not stirred, the gel particles may be agglomerated, and its center part is not easy to be wet by the water, resulting in slow dissolution, which brings trouble to the use. In the production of the general use of high shear dissolution method, that is, in the non-stop high-speed stirring, slowly add the glue powder to the water, continue to stir until it becomes a thick glue. Appropriate heating during the dissolution process, or adding appropriate amount of sugar and other dry powder mixing and dispersing before adding to the water will also help the dissolution of alginate.

 

(i) Alginate

 

Alginate, molecular formula (C6H7O6H)n, white or light yellow powder, insoluble in cold water, soluble in alkaline solution, insoluble in organic solvents. It is odorless and tasteless, or has a slight special odor. pH value of 3% water suspension is 2.0-3.4, and it is precipitated by calcium salt. Alginic acid is a kind of polyglucuronic acid extracted from seaweeds (e.g. kelp, macroalgae, etc.), which can be used as stabilizer, thickener, emulsifier and gel-forming agent in the food industry, and it can be used as thickening stabilizer for ice cream, sauce, jam, bread, noodles, whipping cream, soup, etc.; defrosting adjusting agent for frozen food; suspending agent for soft drinks; coating agent for baked food; emulsifier for pudding and spray-dried cream powder. Emulsifier for pudding and spray-dried cream powder. Alginic acid can also be used in the pharmaceutical and health care industry, as an anti-obesity agent and treatment of gastric disease of new agents have greater medical value, at the same time, it is also the production of alginate propylene glycol ester, alginate triethylamine, alginate dibasic sodium (PSS) and other important raw materials.

 

(B) sodium alginate

 

Sodium alginate, also known as sodium fucoidan, kelp gum, brown algae gum, alginate, white or light yellow powder or particles, odorless, tasteless, soluble in water, its aqueous solution is a viscous colloid, insoluble in alcohol and other organic solvents. The molecular formula is C5H7O4COONa)n. It is widely used in food, medicine, textile, printing and dyeing, papermaking, daily-use chemical industry, etc. It is mainly used in the food industry as stabilizer, thickener, emulsifier, dispersing agent and coagulant in the processing of cold drinks, pastries, candies, instant beverages and foodstuffs, etc. Especially since the 1980s, seaweed has been used in the processing of foodstuffs. Especially since the 1980s, sodium alginate has been continuously expanded in food applications. Sodium alginate is not only a safe food additive, but also can be used as the base material of bionic food or therapeutic food. Since it is actually a natural dietary fiber, it has been reported to slow down the absorption of fatty acids and bile salts, and has the effect of lowering serum cholesterol, blood triglycerides, and blood glucose, which can prevent modern diseases such as hypertension, diabetes, and obesity. It can inhibit the accumulation of harmful metals such as strontium, cadmium and lead in the body in the intestinal tract. It is because of these important roles of sodium fucoidan that it has been increasingly emphasized at home and abroad.

 

(III) Potassium alginate

 

Potassium alginate molecular formula: (C6H7O6K)n, properties: white to light yellow irregular powder, odorless, tasteless, easily soluble in water to form a viscous solution, insoluble in ethanol or ethanol content higher than 30% (wt) of the hydroalcohol solution, insoluble in chloroform, ether and pH less than 3 acid. Potassium alginate can be generally obtained by reacting alginate with potassium carbonate or potassium hydroxide.

 

It can be used as stabilizer and thickener in canned food, ice cream, noodles and other food according to GB2760 of China. Uses: Mainly used in medicine and food industry. Potassium alginate is a kind of natural polysaccharide carbohydrates extracted from seaweeds, which is reported to have the effect of lowering blood fat, blood sugar, cholesterol, etc. It is mainly used in pharmaceuticals and health food.

 

(IV) Ammonium Alginate

 

Ammonium alginate is white to light yellow fibrous powder or coarse powder, almost odorless and tasteless, slowly dissolved in water to form a viscous colloidal solution, insoluble in ethanol and ethanol content higher than 30% (wt) of the hydroalcohol solution, insoluble in chloroform, ether and pH value of less than 3 acid solution. Its industrial production method is generally obtained by neutralizing alginate with ammonia or ammonium carbonate.

 

(E) Calcium alginate

 

Calcium alginate, molecular formula: [(C6H7O6)2Ca]n, white powder to light yellow indefinite powder, odorless, tasteless, insoluble in water and organic solvents, insoluble in ethanol. Slowly soluble in sodium polyphosphate, sodium carbonate solutions and solutions of calcium compounds. Its industrial system is generally obtained by the reaction between alginate and calcium hydroxide or calcium carbonate.

 

Fourth, the rheological properties of alginate and influencing factors

 

There is no correlation between the viscosity of alginate and the ability to gel, in practice, there is no clear boundary between thickening and weak gel, the presence of a small amount of calcium ions can make the viscosity increase, while a large number of calcium ions make the solution into a gel. Pure alginate dissolved in distilled water makes a homogeneous solution with high fluidity. Physical factors that affect the fluid properties of alginate solutions include temperature, shear rate, polymer particle size, concentration, and solvents miscible with distilled water. Chemical factors affecting alginate solutions are: pH, chelates, various cations and quaternary amine compounds.

 

(i) Rheological properties of alginate solutions

 

The concentration of alginate solution is an important factor affecting the rheological properties of alginate solution. For example, the medium viscosity of sodium alginate solution, when the concentration of 0.5%, in the low shear rate range for the Newtonian fluid characteristics, in the high shear rate on the performance of non-Newtonian fluid characteristics; but when the concentration of 2.5%, in both the low and high shear rate are shown as non-Newtonian fluid characteristics. Similarly, a 3% solution of propylene glycol alginate exhibits shear thinning over a wide range of shear rates; whereas at a concentration of l% or less, the solution has an almost stable viscosity and does not exhibit shear thinning at shear rates below lOO s-1.

 

Sodium alginate has a high molecular weight and molecular rigidity, and high apparent viscosity solutions can be obtained even at low concentrations.

 

The viscosity-shear curves of medium-viscosity sodium alginate and potassium alginate are consistent over the entire range of shear rates. The viscosity-shear curves of low-viscosity PGA and sodium alginate essentially overlap over the range of shear rates higher than 10,000 s-1, and bifurcate only at lower shear rates.

 

(II) Factors affecting the rheological properties of alginate solution

 

1. Temperature

 

When the temperature increases, the viscosity of alginate solution decreases, and the viscosity decreases by about 12% for every 5.6℃ increase in temperature. If it is not under high temperature for a long time, the viscosity can be recovered when the temperature is lowered. Heating causes thermal degradation of alginate, the degree of which is temperature and time dependent. Although lowering the temperature of the alginate solution will increase the viscosity, but will not generate a gel, the alginate solution will be frozen, and then thawed and thawed again, its viscosity will not change.

 

2.Solvent

 

The addition of small amounts of non-aqueous solvents that are miscible with water, such as ethanol, ethylene glycol or acetone, will increase the viscosity of alginate solutions and ultimately lead to the precipitation of alginate. The permissible limits of alginate solutions for these solvents are influenced by the source of the alginate, the degree of polymerization, the type of cation present, and the concentration of the solution.

 

3. Concentration

 

Similar to most other food gels, the viscosity of alginates such as sodium alginate, ammonium alginate, potassium alginate and PGA increases with their concentration in aqueous solutions. Of course, there are large differences in the viscosity increase for various viscosity grades of alginates.

 

4.pH

 

Generally speaking, alginate is more stable under acidic conditions, especially for PGA. pH value should be lowered to 3.0 when PGA may gel, higher than 7.0 will be saponification and decomposition, while the pH value of 3.0-7.0 is quite stable, so PGA is very suitable for the application of acidic food.

 

5.Gelation

 

Alginate can react with many high-valent cations (except magnesium) to produce cross-linking. When the content of multivalent cations increases, the alginate solution thickens and forms a gel, which eventually precipitates.

 

All alginate gels are the result of interactions between alginate molecules, and they are thermally irreversible. The structure and strength of the gel can be adjusted by choosing the appropriate gelling agent.

 

Multivalent metal ions, such as zinc, aluminum, copper, in the presence of excess ammonia, can generate complexes with alginate. When ammonia is removed from this system, insoluble alginate is produced. Calcium is most commonly used to change the fluid properties of alginate solutions and gelling properties of polyvalent cations, calcium can also be used to prepare insoluble alginate fibers and films.

 

Addition of calcium to an alginate system can significantly change its gelling properties. However, it must be noted that if the calcium is added too fast, it may lead to local reaction too fast, affecting the uniformity of the whole system, and generating a discontinuous gel. Therefore, try to use a slow dissolution of calcium salts, or add such as sodium tripolyphosphate or sodium hexametaphosphate such as integrators, in order to control the rate of calcium.

 

Several principles used to control gel strength or gel time are:

 

(1) the addition of a chelating agent will weaken the gel-generating effect, but too low an addition of chelating agent may produce a discontinuous gel; (2) lowering the calcium content results in a softer gel, and increasing the calcium content results in a harder gel. However, excessive calcium cuts can lead to the generation of discontinuous gels or precipitates; (3) in an acidic system, the addition of slowly dissolvable acids can accelerate the formation of gels; (4) the higher the viscosity of alginate, the more brittle the gel formed; (5) the closer the calcium content is to the amount of chemical calculations required for the reaction with alginate, the higher the likelihood of producing dehydration contraction.

 

6. Chelating agent

 

The addition of a chelating agent to an alginate solution serves to chelate it with residual polyvalent cations and to prevent the alginate from reacting with these polyvalent cations. Sodium alginate solutions with low calcium content show very little change in viscosity when chelating agents are added. In contrast, when a calcium alginate-sodium alginate solution is added to a chelating agent, the viscosity changes significantly. The addition of chelating agent can make the fluid of alginate solution closer to the Newtonian fluid.

 

7. Monovalent salts

 

The addition of monovalent salts will reduce the viscosity of dilute alginate solution. The concentration of monovalent salts in the solution reaches 0.1 mol / L, the greatest effect on viscosity. In the concentrated solution, this effect is less significant. The main factors affecting the role of monovalent salts on alginate solution are: the type of salt, the source of alginate, the degree of polymerization and concentration.

 

1. Gelation characteristics and methods of alginate

 

(I) Gelation mechanism

 

In the food industry alginate is mainly used as gelling agent and thickener. In the application of alginate, gelling is widely used. Water-soluble alginate reacts with calcium ions and can form gel very quickly. However, the mechanism of gel formation and its influencing factors are more complex.

 

Alginate gel formation belongs to chemical gelation. Ionic macromolecules (such as alginate) in the presence of high-valent metal ions can form gels, and there is no relationship with the temperature. Both sodium alginate and low ester pectin obtain a special kind of gel by a chemical reaction with calcium ions while forming crosslinks. It is generally believed that this cross-linking is due to the interaction of two carboxyl groups on neighboring polymer chains with calcium ions to form ionic bridges or chelation with calcium ions through hydroxyl and carboxyl groups on each pair of polymer chains.

 

The properties of alginate (salt) mainly depend on its viscosity and the ratio of mannuronic acid to guluronic acid (M/G); the higher the molecular weight, the higher the viscosity, and by controlling the degree of molecular weight degradation through the process conditions, it is possible to obtain different viscosity grades of alginate, however, the M/G ratio, which determines the size of its gel-forming ability, depends on the source of the different species.

 

Usually, high M-type is commonly used as a thickener while high G-type is used as a gelling agent, because in the “egg carton” model interpretation of alginate gelation theory, guluronic acid-linked fragments have a spatial configuration that accepts calcium ions, whereas the mannuronic acid fragments tend to be ribbon-shaped and are less likely to accept calcium ions. Calcium ions form a high-strength brittle gel with high G-type alginate with good thermal stability, which can become a thermally irreversible gel; while with high M-type, it generates a weakly strong elastic gel, which is more suitable for thawing or freezing treatments, on the other hand, the gel strength of high M-type is higher than that of high G-type when the concentration of calcium ions is low, and as the concentration of calcium ions increases, the gel strength of high G-type rises rapidly and exceeds the gel strength of high M-type significantly With the increase of calcium ion concentration, the gel strength of high G-type increased rapidly and greatly exceeded that of high M-type, while the increase of high M-type was slow; when the increase of calcium ion concentration exceeded the maximum amount needed for gel formation, it would lead to a decrease in gel strength instead.

 

The concentration of calcium ions in the system has a great influence on the practical use of alginate. Adding different amounts of calcium ions to the 0.5% concentration of high M sodium alginate solution showed that: the solution was pseudoplastic at the level of 0-50 ppm, thixotropic at the level of 50-350 ppm, and began to form a gel at the level of 350 ppm or more. In the application of different calcium salts or chelating agents to control the speed and time of gel formation, commonly used calcium salts with different solubility: such as CaCL2, in the neutral pH all dissociate into calcium ions, and can quickly react with the alginate to form a gel; Calcium sulfate dihydrate, only a small amount of calcium ions dissociate into calcium ions in the neutral pH, but in the acidic pH can be dissociated in all the control of the specific pH conditions, to maintain only a certain amount of calcium ions with alginate in the system, and to maintain a certain amount of calcium ions with the gel. Control of specific pH conditions to maintain only a certain amount of calcium ions in the system and alginate reaction, the reaction of calcium ions will be consumed from the further dissociation of calcium sulfate equilibrium will be replenished in order to maintain the same concentration of calcium ions; dicalcium phosphate, its solubility at neutral pH is zero, with the increase in acidity of the system, the number of free calcium ions rise; the use of chelating agents, such as sodium pyrophosphate, sodium citrate, etc., and their chelating capacity of calcium ions by the pH; use of acidifying agents such as gluconic acid – sodium citrate, etc., and the ability of chelating calcium ions by pH; use of Acidifying agents such as glucono-δ-lactone, whose degree of acidification is controlled by the temperature of the system; therefore, the skillful use of these factors can be used to control the speed, time and strength of the gel.

 

The amount of calcium ions required for gel preparation depends entirely on the gel preparation conditions. For example, at a pH of 4.0, a gel can be produced from a given amount of alginate with a chemically calculated amount of calcium ions ranging from l0% to 15%. However, at a pH of 7.0, twice the amount of calcium ions is required (about 2% calcium by sodium alginate dosage). Under acidic conditions, some of the carboxyl groups are protonated, reducing the interchain repulsion and thus lowering the total amount of calcium required to form the gel.

 

The way to increase the strength of the alginate gel is to increase the concentration of alginate or calcium ions as well as to lower the temperature of the system (freezing). To weaken the strength of the alginate gel, the following methods can be used: decreasing the concentration of alginate or calcium ions, increasing the temperature of the system, increasing the content of soluble components in the system, adding high relative molecular mass polymers, and adding chelating agents.

 

(ii) Gum formation methods

 

Almost all soluble alginates are capable of forming gels, and there are three different methods by which alginates can be made to form gels.

 

1. Dispersive Gelation

 

Dispersive coagulation is the simplest technique, i.e. a gel is formed when calcium ions diffuse into the hydrated alginate. Because the diffusion process is slow, it can only be used for thin strips such as bell pepper strips, or to coat the surface of onion rings with a thin layer of gel. If the calcium ion concentration in the gel is increased, the rate of dispersion can be increased. There is a limit to this, however, because the most commonly used source of calcium ions is calcium chloride, and when its concentration is too high it can affect the flavor of the food. Another commonly used coagulant aid is calcium lactate, which has the disadvantage of very low solubility in water (about 5%).

 

2. Internal coagulation

 

Internal coagulation generally takes place at room temperature with a controlled release of calcium from the ingredient. This is commonly used in the preparation of fruits, meats and many cold prepared desserts. Calcium sulfate (typically containing two water molecules) and calcium hydrogen phosphate are the most commonly used calcium sources. The proportion of calcium required by the alginate molecule depends largely on pH, molecular weight, size of the plasma point and solubility of the calcium salt itself. The smaller the particle size and the lower the pH, the faster the calcium is released. Calcium needs to be incorporated in production to control the rate of release so that the seaweed gel can be dissolved before the reaction between seaweed gel and calcium begins.

 

Once the amount of seaweed gum and calcium salt has been determined, increasing the amount of integrator reduces the gelation rate. The resulting gel is weaker because the final distribution of calcium ions between the alginate and the integrator is more in favor of the latter. Therefore, the use of an integrating agent to control the gelation reaction is only necessary if premature gelation and irreversible rupture of the gel structure need to be prevented during mixing. Obviously, if efficient rapid mixing equipment is used, only a small amount of integrant is required and only a small amount of calcium salt is dissolved during mixing. In this case, rapid coagulation results in a firm gel. Typical integrators for foodstuffs are sodium hexametaphosphate, tetrasodium pyrophosphate and sodium citrate.

 

3. Cooling Gelation

 

The third method of preparing an alginate gel is to dissolve the ingredients for the gel, including the alginate, calcium salts, acids, and integrators, in hot water and then allow the solution to cool to allow coagulation. Although the calcium ions required for the coagulation reaction are already in solution with the alginate, they cannot coagulate at high temperatures because the chains of alginate are linear when there is too much heat. Only when that solution is cooled can the internal association of the chains caused by the calcium be realized. Unlike the gel of gelatin, the gel of alginate is irreversible when heated, so it can be used for sweets in some areas where higher ambient temperatures are sufficient to melt the gel made from gelatin. The role of calcium salts and integrators in such systems is the same as in the internal gelation described above.

 

The dehydrating shrinkage effect or water loss in such gels is minimal. This is due to the stability caused by the calcium required to form the gel, allowing all the alginate molecules to form a thermodynamically stable network while forming the gel.

 

In diffuse coagulation, the first to act are those alginate molecules that are in close proximity to the calcium ions in the coagulant, whereas in internal coagulation, the first to act are the alginate molecules in close proximity to the tiny plasmas of the dissolved calcium salts. Thus, in either diffuse or internal condensation, the alginate molecules have no chance to line up in a straight line during the whole process, and thus their gel network is built on an unstable basis. This instability, in general, exacerbates gel shrinkage and dehydration contraction.

 

Corresponding to the above three methods, in specific food processing applications, the gel formation method can also be divided into (1) infiltration method: through the calcium ions constantly penetrate into the alginate solution and become a gel, such as for fruit preservation (will be the fruit first through the sodium alginate solution and then into the calcium-containing ions into the solution, the surface of the fruit that is the formation of a gel, drying that is to become a thin film and thus prevent the fruit from respiration). (2) Mixing method: add high G-type sodium alginate and slightly soluble calcium salts (in neutral pH system) or insoluble calcium salts (in acidic pH system) in the system, and control the gel characteristics by changing the temperature, acidity, effective concentration of calcium and reaction time; such as for the reorganization of minced meat (94% of minced meat, 0.9% of high G-type sodium alginate, 0.09% of sodium pyrophosphate, 0.9% of calcium sulphate dihydrate and 4% of water. The dissociation of calcium sulfate is broken by the formation of a gel from calcium ions and sodium alginate and it is necessary to dissociate more and more calcium ions, and the mixture is placed in a container of a certain shape, and after the necessary time a well-structured whole piece of meat is obtained). Another method of using a mixture of two phases, A and B, in an acidic system to produce a fruit glass filament product is also helpful in understanding the specific application.

 

Dicalcium phosphate in phase A does not react with sodium alginate to form a gel under neutral conditions, and when the two phases are mixed by high-speed stirring and then extruded through a long tube porous nozzle, a glassy filamentous gel has been formed because the two-phase mixing turns the system into an acidic system, and the dicalcium phosphate begins to release calcium ions to react with the sodium alginate to form a gel, and the strength of the gel rises with the migration of time of conveyance on the conveyor belt. (3) cooling method: due to the high temperature, intense intermolecular Brang movement can not make calcium ions and sodium alginate to form a gel structure arrangement, so all the necessary components can be added to the high temperature solution system, to be the solution temperature drops to the gel point, that is, the formation of heat will not melt even if heated thermally irreversible gel.

 

In addition, alginate and other food gels have compatibility with high ester pectin can be formed in the system does not contain calcium ions in the formation of thermally irreversible gel, for the production of low-calorie jam; and high ester pectin alone may be in the high sugar-containing system in order to form a gel.

 

Sixth, the role of alginate and protein between the

 

Alginate, similar to other water-soluble gels, can act with proteins. The main use of this action can be used for precipitation recovery of proteins. It is generally believed that in the controlled action of alginate and protein, hydrogen bonding and van der Waals forces are important factors leading to this action. It also depends on the charge carried by the macromolecule, with the maximum interaction occurring at the smallest point of charge. Measurements of the viscosity of alginate-protein systems at different pH show that when the pH is lowered close to the protein iso-point, the viscosity of the system increases due to the formation of soluble complexes. If the pH is further reduced, precipitation of the complex occurs due to the loss of all the charge carried. In addition to being used to precipitate proteins, alginate can also be used to inhibit protein precipitation under appropriate conditions. Under the isoelectric point of proteins, the addition of an appropriate amount of alginate can lower the isoelectric point and inhibit the precipitation of proteins in order to maintain the proteins in solution. At lower pH (pH 3.5 to 4.0), alginate has a greater ability to precipitate proteins than pectin and carboxymethyl cellulose, which is mainly due to the fact that in the chain of the alginate molecule, the charge carried by the end group of each unit is higher than that of both pectin and carboxymethyl cellulose. In addition, the space configuration is also an important factor.

 

Seven, alginate in the food industry applications

 

The main varieties of alginate used in the food industry are: sodium alginate, potassium alginate, calcium alginate, and propylene glycol alginate. The most important role of alginate in food processing is gelation, i.e. the formation of edible gels. Secondly, the thickening and film-forming properties of alginates are also widely used in the food industry. Sodium alginate in the food industry is often used as a thickener (sauces, salad dressings, fruit drinks thickening, etc.), stabilizers (in ice cream), film-forming agent (used in sandwich pastries, frozen fish, meat, etc. to prevent water infiltration, candy anti-sticking packaging, fruit preservation) and water-retaining agent (used in frozen products and dairy products frozen sweets) and so on.

 

(I) The main role of alginate in food

 

1. Stabilization

 

Sodium alginate instead of starch, gelatin for ice cream stabilizer, can control the formation of ice crystals, improve the texture of ice cream, but also to stabilize the sugar-water sorbet, ice and fruit dew, frozen milk and other mixed drinks. Many dairy products, such as refined cheese, guandan cream, cheese, etc. The stabilizing effect of sodium alginate can prevent the adhesion of food and packaging, can be used as a dairy jewelry cover, which can make it stable and prevent frosting pastry cracking.

 

2.Thickening

 

Sodium alginate can be used in salad (a kind of coleslaw) sauce, pudding (a kind of sweet snacks), jam, ketchup and canned products of the thickening agent, in order to improve the stability of the product properties, reduce the liquid seepage.

 

3.Hydration

 

Add sodium alginate in the production of noodles, vermicelli, rice flour can improve the adhesion of the product organization, so that it is strong, bendable, reduce the rate of breakage, especially for the gluten content of lower flour, the effect is more obvious. Add sodium alginate in bread, pastries and other products, can improve the internal organization of the product uniformity and water holding effect, prolong the storage time. Added in the frozen confectionery products can provide thermal fusion protective layer, improve the flavor escape, improve the melting point of the performance.

 

4.Gelation

 

Sodium alginate can be made into a variety of gel food, maintain a good colloidal form, no ooze or shrinkage, suitable for frozen food and artificial imitation food. It can also be used to cover fruits, meat, poultry and aquatic products as a protective layer, with no direct contact with the air to extend the storage time. It can also be used as a self-coagulating forming agent for icing of bread, stuffing filler, coating layer of confectionery, canned food, etc. In high temperature, freezing and acidic medium can still maintain the original shape. Can also be made instead of agar with elasticity, non-stick teeth, transparent crystal candy.

 

(B) the specific application of alginate in food

 

1. Application in ice cream

 

Use sodium alginate instead of gelatin, starch and other cold drink food stabilizers, can make the ingredients mixed uniformly, easy to mix and dissolve, in the freezing can be adjusted to flow, so that ice cream products have a smooth appearance and melting characteristics, but also without aging time, expansion rate is also larger, the product texture is smooth, delicate, good taste, the dosage is also lower than the other commonly used stabilizers.

 

2. Application in bakery products

 

Adding sodium alginate to baked food can make their quality improve greatly. Used in the production of cookies, egg rolls can reduce its crushing rate, the test result is that the crushing rate can be reduced by 70% to 80%, the appearance of the product is smooth, moisture-proof to improve; when applied to the production of bread, cake can make them get further expansion, volume increase, texture loose, reduce the slices when the fall of the particle debris, but also to prevent aging, prolonging the preservation period.

 

3. Application in dairy products and beverages

 

At present, yogurt as a high nutritional value of cow’s milk is very popular among consumers, and yogurt is also one of the important sources of beneficial lactic acid bacteria. It is to milk by microbial (generally lactic acid bacteria) fermentation, so that it produces a special flavor of dairy products. Fruit juice is sometimes added to it to increase its nutritional value and flavor. Alginate can play a stabilizing effect on yogurt products in a wide pH range, in the range of pH 3.9 to 4.9, can play this role. Frozen buttermilk stabilized with alginate has a good texture without stickiness or stiffness, and is sticky and sluggish when stirred. Alginate can also prevent the phenomenon of viscosity loss in the sterilization process of yogurt products． Add 0.25% to 2% alginate in milk, and its finished products are stored at high temperature for 30d, and its flavor will not change. In addition to yogurt products, other beverages can also use alginate. For example, a crisp, fruity syrup can be made from sodium alginate and saccharin, supplemented with ingredients. These syrups have a smooth, even and good taste and are stable and not easily layered.

 

4. Application in cold food and snacks

 

Alginate has the ability to form gel easily, so it can be widely used in the production of sweet snacks, specifically for the manufacture of cold milk pudding, pie folder, frozen sweets. Sodium alginate and sugar mixed with water to dissolve, add crushed fruit with color, spices and other additives, and then add edible calcium organic acid salt solution, the formation of gel, in 70 ~ 100 ℃ under the heat for 2 minutes, can be made of delicious fruit sweets.

 

5. Application in pasta products

 

As sodium alginate has strong hydrophilicity and adhesion, it can be added into noodles, noodles and other noodle products to improve the toughness of the products, reduce the rate of breakage, not sticky after cooking, not rotten soup, storage resistance and good taste. Especially for the flour with low gluten rate, the effect is better.

 

6. Application in beer and other alcoholic beverages

 

Add sodium alginate in beer can play a stabilizing effect on the beer foam, and transparency is also increased, the preservation period is extended, in other alcoholic beverages such as sake, fruit wines and champagne and other alcoholic beverages often due to the presence of more acid and pigmentation and turbidity, if you add an appropriate amount of sodium alginate, can be very good to play a role in clarification. In addition, alginate can also remove tannins and nitrogenous substances in wine.

 

7. Application in artificial food

 

The application of alginate can also produce artificial jam, margarine, artificial intestinal coating and artificial fruit and other artificial food. As long as the required sweetener and food coloring, spices into the solution of sodium alginate, mix well, add calcium, in a short period of time can form a good artificial jam; alginate can be used as a thickener or emulsifier for margarine, usually using propylene glycol alginate, and sometimes also using sodium alginate.