Sodium alginate is a by-product of iodine and mannitol extracted from kelp or sargassum of brown algae. Its molecule is composed of β- D-mannuronic acid( β- D-manuronic, M) and α- L-glucuronic acid( α- L-guluronic, G) is connected by pressing the (1 → 4) key. The aqueous solution of sodium alginate has a high viscosity and has been used as a thickener, stabilizer, emulsifier, etc. of food. Sodium alginate is a non-toxic food, which has been included in the United States Pharmacopoeia as early as 1938. Sodium alginate contains a large amount of - COO -, which can show polyanion behavior in aqueous solution and has certain adhesion, and can be used as a drug carrier for treating mucosal tissue. Under acidic conditions, - COO - changes to - COOH, the degree of ionization decreases, the hydrophilicity of sodium alginate decreases, the molecular chain shrinks, and the pH value increases, the - COOH group continuously dissociates, the hydrophilicity of sodium alginate increases, and the molecular chain extends. Therefore, sodium alginate has obvious pH sensitivity. Sodium alginate can quickly form gel under extremely mild conditions. When cations such as Ca2+and Sr2+exist, the Na+on the G unit will exchange with divalent cations, and the G unit will stack to form a cross-linked network structure, thus forming a hydrogel. The conditions under which sodium alginate forms gel are mild, which can avoid the inactivation of sensitive drugs, proteins, cells, enzymes and other active substances. Because of these excellent properties, sodium alginate has been widely used in food industry and medicine.
1. Application in food
Sodium alginate is used to replace starch and gelatin as the stabilizer of ice cream, which can control the formation of ice crystals, improve the taste of ice cream, and also stabilize mixed drinks such as sugar-water ice cream, ice fruit jelly, frozen milk, etc. Many dairy products, such as refined cheese, whipped cream, dry cheese, etc., can prevent the adhesion between food and packaging by using the stability of sodium alginate, and can be used as the covering of upper dairy jewelry, which can keep it stable and prevent the cracking of frosted pastry.
Sodium alginate can be made into various gel foods to maintain good colloidal form without seepage or shrinkage, and is 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, without direct contact with the air, and prolong the storage time. It can also be used as the sugar coating of bread, filling, pastry coating, canned food and other self-coagulating agents. The original shape can still be maintained in high temperature, freezing and acidic media. It can also be made into elastic, toothless, transparent crystal soft candy instead of agar.
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