Application of sodium alginate gel in meat products

　　The manufacturer of sodium alginate tells you that sodium alginate is a polysaccharide carbohydrate extracted from kelp or Sargassum of brown algae. It is not only a safe food additive, but also a base material of bionic food or therapeutic food, and is widely used as stabilizer, thickener, binder, dispersant and coagulant in food industry. In this paper, the gel characteristics of sodium alginate and its application in meat products are reviewed to provide reference for relevant researchers.

　　Gel properties of sodium alginate

　　Divalent cations can react with sodium alginate to form transparent thermally irreversible gels at room temperature, such as Ca2+,Pb2+and Cu2+. Although the binding ability of Pb2+and Cu2+with sodium alginate molecules is stronger than that of Ca2+,the gel formed has better gel strength, but Pb2+and Cu2+have certain toxicity, which limits their application range. When they are applied in food, Ca2+is usually used as the cross-linking agent of sodium alginate.

　　Gel mechanism of sodium alginate

　　Other hydrocolloids, such as agar, carrageenan and sodium alginate, have different gel mechanisms. For example, agar needs to be heated to boiling, then cooled to 35℃ to form gel, and when its gel is heated to 85℃, the agar gel will melt. Agar molecules are distributed in random coil in the solution. With the increase of temperature, the molecular movement intensifies, and the random coil structure is destroyed. After that, the temperature of the system decreases, and the intensity of the movement of agar molecules decreases. The molecules intertwine with each other to form a spiral, and the spiral reunion forms a gel. The reason why sodium alginate forms a gel is that Ca2+ interacts with sodium alginate molecules electrostatically, so the gel does not need to be heated, and the obtained gel is thermally irreversible, which is the biggest advantage of sodium alginate gel over other hydrocolloid gels.

　　Main influencing factors of sodium alginate gel formation

　　The gel formation of sodium alginate is mainly influenced by five factors: the type of sodium alginate, the type of calcium source, calcium ion chelating agent, temperature and pH value.

　　Types of sodium alginate

　　The guluronic acid (G unit) content and viscosity of sodium alginate will affect the gel effect. The content of G units in different kinds of sodium alginate is different. According to the principle of gel formation between sodium alginate and Ca2+,G units play a major role in the gel, so the proportion of G units in sodium alginate molecules is an important factor affecting the gel effect.

　　The gel prepared by high G-type sodium alginate has high rigidity, brittleness and good thermal stability, while the gel formed by high M-type sodium alginate has poor mechanical strength but good elasticity. At the same concentration, the viscosity of sodium alginate solution varies with the molecular weight of sodium alginate. The higher the degree of polymerization of sodium alginate, the greater the molecular weight, and the greater the viscosity at the same concentration. The polymerization degree of sodium alginate can be controlled by controlling the extraction process, and sodium alginate with different viscosities can be produced. The longer the molecular chain, the closer the sodium alginate molecules are when forming gel, and the greater the mechanical strength of the gel.

　　Calcium source species

　　According to the types of calcium sources, the methods of preparing calcium alginate gel are different. The first is calcium salts with good solubility at neutral pH value, such as calcium chloride and calcium lactate. The traditional cross-linking agent used to cross-link sodium alginate with Ca2+is generally calcium chloride. The biggest disadvantage of using calcium chloride is that the gel rate is too fast, and the sodium alginate solution contacted with Ca2+immediately forms a gel, which blocks the subsequent gel reaction, resulting in a gradient change in the conversion rate of sodium alginate, and it is impossible to obtain a uniform gel with a good three-dimensional structure. The other is calcium salt with poor solubility, such as calcium sulfate, which has low solubility in water. Calcium sulfate is insoluble in water, and its dissolution rate is very slow, which can provide a certain time for the dissolution of sodium alginate molecules, but the dissolution rate of calcium sulfate is still faster than that of sodium alginate. If sodium alginate and calcium sulfate powder are dissolved together, the dissolved Ca2+ and sodium alginate will form a gel to block the subsequent gel reaction. The gel prepared by this method is uneven and the gel strength is not high.

　　In addition, the addition of calcium source will also affect the gel effect. With the increase of sodium alginate concentration, its water holding capacity, elasticity and toughness and gel strength are gradually enhanced. Mainly when the concentration of calcium ion is constant and the concentration of sodium alginate is low, the exchange between sodium alginate and calcium ion is incomplete, and the gel formed is weak and weak. With the increase of concentration, enough sodium alginate exchanged with calcium ions, and the spatial network structure of calcium alginate was compact, and the interaction between sodium alginate macromolecules was strengthened, the water holding capacity was enhanced, the gel strength was increased, and the elasticity and toughness were also better.

　　Calcium ion chelating agent

　　Calcium chelating agent can chelate Ca2+in water, so that it can't combine with sodium alginate. By competing for Ca2+with sodium alginate, the rate of gel formation is controlled, so that sodium alginate has enough time to dissolve, which can effectively improve the quality of gel. The disadvantage of this method is that chelating agents are introduced, and Ca2+is wasted, so that the dosage of additives increases and the efficiency decreases.

　　temperature

　　Temperature has an indirect effect on the gel formation process of sodium alginate. Increasing the reaction temperature of the system can accelerate the dissolution rate of calcium salt and sodium alginate, increase the intensity of molecular movement in the system, and accelerate the combination of Ca2+and sodium alginate molecules, thus accelerating the gel process. However, when the system temperature exceeds a certain limit, the gelation process will not occur. Alginate has a method of cooling and condensing to form gel. This method is to dissolve sodium alginate, acid, calcium salt and chelating agent in hot water, and then cool the solution to form gel. When dissolved together in hot water, although the sodium alginate solution has been exposed to Ca2+,it can't combine with Ca2+when there is more heat energy in the molecular chain of sodium alginate. When the solution is cooled to a certain temperature, the sodium alginate molecules can react with Ca2+to form a gel. Although sodium alginate cannot form gel at high temperature, when alginate gel is formed, its gel is thermally irreversible and can maintain its physical form at high temperature.

　　pH value

　　Adding acidic substances and lowering the pH value of the system can transform some calcium salts which are insoluble in neutral and alkaline conditions into calcium salts with good solubility. For example, if calcium hydrogen phosphate and sodium alginate are mixed in water and then added into lactic acid, the insoluble calcium carbonate can react to produce calcium bicarbonate or calcium lactate with relatively good solubility, thus releasing Ca2+ and forming gel with sodium alginate solution.

　　Application of sodium alginate in meat products

　　Sodium alginate can be made into various gel foods, which maintain good physical morphology and are not easy to ooze or shrink, and are suitable for frozen foods. Adding sodium alginate to meat products can improve the physical properties of meat products, increase the viscosity and give them a good taste. At the same time, it can increase the water holding capacity and tenderness of meat products, increase the yield and reduce the loss of nutrients and flavor substances.

　　The gel formed by sodium alginate and Ca2+is often used as a binder for meat products, which can improve the texture properties of meat products and strengthen the bonding between meat pieces. Sodium alginate, calcium ions, other colloids and phosphates can be used as water-retaining agents for meat products. Improve the physical properties of meat products, increase viscosity and give them a good taste, at the same time, it can increase the adhesiveness, water holding capacity and tenderness of meat products, reduce the loss of nutrients and improve product quality.

　　Sodium alginate is used as binder.

　　Recombined meat is to extract the mechanism protein from muscle fiber by means of machinery and adding auxiliary materials, and to change the original structure of meat by using the adhesive effect of additives, so that muscle tissue, adipose tissue and connective tissue can be reasonably distributed and transformed, so that meat particles and pieces can be recombined, sold directly after freezing or preserved and improved by preheating treatment, so gel network structure is needed to combine meat with meat. However, sodium alginate can cross-link with calcium ion. With the increase of calcium ion content, sodium alginate solution will thicken and form gel. Therefore, the gel formed by sodium alginate and calcium ions is often used as a binder.

　　Sodium alginate is used as water-retaining agent.

　　The water holding capacity of meat products is an important index to measure the quality of meat products, which not only affects the edible quality of meat products such as color, aroma, taste, nutritional components, juiciness and tenderness, but also affects the economic value of products. China loses about 3.1 million tons of meat every year due to muscle dehydration, which brings huge losses to enterprises and the country. Therefore, efforts must be made to improve the water holding capacity of muscles. By studying the effects of adding colloid to calcium alginate and phosphate on the properties of reconstituted beef rolls, it was found that the combination of calcium alginate and gellan gum significantly improved the cooking yield. By using an edible coating (calcium alginate) to improve the quality of frozen meat, it was found that sodium alginate could reduce the thawing loss of frozen meat, maintain the functional characteristics of frozen meat and affect the solubility of total protein.

　　Some researchers studied the effects of sodium alginate with different mesh sizes on the water-holding capacity and texture of meat products. The results showed that the effects of sodium alginate with different gel strength on the water-holding capacity of meat products were different under the same technological conditions. Through the analysis of the compound experiment, it was known that the combination of 0.2% sodium alginate with 170 mesh sizes and 0.3% carrageenan could greatly improve the quality and texture of meat products, and its water-holding capacity reached the best. The study on the phosphate-free water-retaining agent and binder for mutton shows that the water-holding capacity and yield of the mutton samples prepared with sodium alginate, xanthan gum, carrageenan and sodium caseinate are significantly higher than those of blank mutton samples and mutton samples injected with mixed phosphate solution, and the phosphate-free water-retaining agent for calcium alginate is still effective in improving the water-holding capacity and yield of mutton after freezing treatment. The researchers improved the water retention of beef and pork by adding starch, protein powder, sodium alginate and calcium salt, carbonate and phosphate. Sodium alginate and gellan gum were used as fat substitutes to improve the quality of low-fat meat emulsion products.

　　Concluding remarks

　　Sodium alginate is a hydrophilic colloid, which can form gel with calcium ions, and has synergistic effect with gelatin, pectin, konjac gum, carrageenan, gellan gum and other colloids. When used in meat products, it can form a dense and stable network structure, and improve the gel strength, cohesiveness and water-holding performance of meat products. Sodium alginate and its compound products will have a good application prospect in meat products in the future.