Agar is a hydrophilic colloid extracted from red algal plants and is one of the most widely used seaweed gums in the world, having been first used in the food industry.

Agar has proved its food safety through hundreds of years of application all over the world, and has been approved by the United Nations World Health Organization for use in the food industry. At the same time, it has also been approved by China, Britain, the United States, France and other countries with regulations.

It has a wide range of applications in the food industry, pharmaceutical industry, daily chemical industry, biological engineering and many other aspects.

In the food industry, agar is used as gelling agent, increasing agent, thickening agent, emulsifier, stabilizer, excipient, suspending agent, water retention agent, can obviously change the quality of food, improve the grade of food, become an important food additives.

Physical and chemical properties of agar

1. Solubility
At room temperature, agar is insoluble in water and inorganic and organic solvents, it is only slightly soluble in ethanolamine and formamide, but soluble in water and some solvents under heating conditions.

Dry agar at room temperature can absorb water to dissolve, water absorption rate of up to 20 times, heated to 95 ℃ can be dissolved in water to form a solution, agar solution at room temperature can form a gel, compared with other substances that can form a gel, in the same concentration of the strongest gel ability , even if 0.1% of the agar solution can be solidified at about 30 ℃.

Agar can also be dissolved in boiling low concentration ethanol (30%~50%) solution. It can be precipitated by salinization in certain highly concentrated electrolyte solutions, such as sodium sulfate, magnesium sulfate, or ammonium sulfate. It has been found that agar can also be dissolved in a variety of other solvents.

2.Flocculation
The addition of 10 times the volume of ethanol, isopropanol or acetone to an agar solution can cause the agar to flocculate and precipitate out of the aqueous solution. Similarly, saturated solutions of calcium sulfate, magnesium sulfate or ammonium sulfate can cause salting out of agar solutions.

Utilizing this property, it can be used for agar gel dehydration in the agar extraction process.

3. Gel temperature hysteresis
Agar gel is a thermoreversible gel, the gel melts when heated, and solidifies when left cold, and can be repeated. The freezing point of agar solution is generally between 32℃-43℃, while the melting point of agar gel is generally between 75℃-90℃.

The melting point is much higher than the freezing point is agar’s unique phenomenon, called “hysteresis phenomenon”, agar’s superiority in many applications is reflected in its high hysteresis.

4.Viscosity
The viscosity of aqueous agar solution (sol) varies with the type of raw materials, raw material quality, extraction conditions, solution pH, the amount of inorganic salts, as well as the determination of agar concentration, temperature and the addition of electrolytes.

In general, the viscosity of the solution of natural polysaccharides with strong coagulation ability is lower, and agar with strong coagulation ability has a lower viscosity.

The viscosity of industrial agar is lower due to the fact that it is damaged to a certain extent by chemical reagents during the extraction process. In addition, agar solution by high temperature, electrolytes, inorganic acids or acidic salts, agar viscosity decreased significantly.

5. Non-acidic degradation
A large number of viscosity, diffraction and gel strength experiments and studies have proved that the stability of pure dry agar is very good and it is difficult to degrade at room temperature.

But contains impurities, high temperature, ultrasonic, strong γ-ray, strong stirring and other factors can make the agar molecular chain breakage and degradation, so that agar deterioration of certain physical and chemical properties.

6. Gel
The biggest feature of agar is that it has gel, even if the concentration of 0.004% agar solution, at room temperature can also form a gel, compared with other substances that can form a gel, in the same concentration of its gel strength is the largest. Agar gel formation, without any coagulant, the size of the gel strength and the type of raw materials, growth environment, collection season and extraction methods, etc., but also its chemical composition and structure are closely related.

Application in food industry

Agar has the stability of gelation and gel, in the food industry, it has the effect of increaser, thickener, emulsifier, gelling agent, stabilizer, excipient, suspending agent, water retention agent, and it is widely used in the food industry.

1. Application in candy
Agar as a gelling agent in the candy industry, mainly used in the manufacture of soft candy. According to the gelation ability of agar, the dosage of agar in fudge is generally 1%-2.5%, and the carbohydrates are mainly sucrose, supplemented by starch syrup, and the ratio is about 3:2.

The transparency, quality and taste of soft candy made with agar are superior to other soft candies. Although agar has long been used as a traditional gel material in confectionery production, practice has shown that its taste characteristics are relatively single, and in recent years, it is also common to add gelatin, modified starch, fruit juices/purees or melons and fruits, etc., which contributes to the diversity of the composition of the materials used in confectionery and is conducive to the improvement of the flavor and mouthfeel.

Gu Yong et al. developed pumpkin fudge, the ratio of sucrose 200g, agar 15g, pumpkin 250g, citric acid 0.3g, to get sweet and sour mouthfeel, golden color, chewy and delicate, with good elasticity and toughness of pumpkin fudge.

2. Application in canned food
In the canned poultry and meat, agar as a gelling agent and excipient, can be formed for the effective bonding of broken meat gel, eliminating the canned food tissue brittle. Its dosage is 0.2% -2.0% of the broth in canned food.

In the eight treasures porridge, silver ear bird’s nest, soup canned food, the use of 0.3% – 0.5% of agar as a thickener, stabilizer, can improve the taste, so that the other additives dispersed uniformly, to prevent precipitation, delamination.

3. Application in beverage
Agar can be used as a suspending agent in beverage products to make the solids in beverages suspended uniformly without sinking. Its suspension time and shelf life is long, other suspending agents can not be replaced, product transparency, fluidity will be better, smooth taste without odor.

In the fruit drink shows excellent suspension effect, the use of concentration of 0.001% -0.005% can make the fruit particles suspended uniformly.

4. Application in jelly
Adding agar in the manufacturing process of jelly can be used as stabilizer and gelling agent, which can make the particles suspended uniformly, without precipitation and delamination. According to the gelling ability of agar, the general dosage is 0.15%-0.3%.

5. Application in cold drink
Agar used in cold drink food, such as popsicles, ice cream and other frozen products, can reduce ice crystals, improve the resistance to heat melting, so that the product is more refreshing.

In the production of ice cream, agar can improve the organization of ice cream, improve the viscosity and expansion rate of ice cream, prevent ice crystal precipitation, so that the organization of the product is delicate and light and smooth, and the amount of its use is about 0.3%. Agar and acacia bean gum, gelatin matching, in the cold drink food texture and flavor stability plays an excellent role, and can prevent dehydration shrinkage and surface crusting.

As a stabilizer, the optimal concentration is: agar 0.12%, acacia bean gum 0.07%, gelatin 0.2%.

6. Application in baked goods
Agar can be used as filler, bulking agent and water retention agent, widely used in a variety of baked goods. Such as baked goods production plant will be agar for cookies, cream sandwich pie shell, pie, pastry sweetheart surface layer of puff pastry, meringue tube and so on. As a slightly binding additive: agar has no nutritional value, but also as a filler and bulking agent, can replace the starch to manufacture cereal paste, no starch bread and after-dinner snacks, made of low-calorie food, but also on the bread and cookies also play a role in moisturizing, insurance.

In baked goods, the amount of agar used is generally 0.1% -1.0%.

7. Application in dairy products
Agar can effectively reduce the dairy products from the pulp, enhance the stability and emulsification, widely used in dairy products. In the French soft white cheese, cream cheese, fermented milk products add agar, with good stability and toughness, but also help to improve the consistency of cheese and slicing. In dairy products, the amount of agar is generally 0.05% – 0.85%, and mannan gum, xanthan gum compound use better results.

8. Application in sugar-coated foods
In sugar-coated food, agar can be used as a stabilizer of sugar coating, but also to prevent the adhesion of food and packaging. The content of agar in sugar-coated food is usually between 0.2% -0.5%.
Based on the amount of sugar needed, agar can be used as a stabilizer for transparent icing of oil cake when the concentration of agar reaches 0.5%-1.0%. The agar stabilizer improves the viscosity of the transparent icing and the adhesion on the surface of the oil cake, which induces the gel to solidify more quickly and increases the flexibility in order to reduce the surface defects and cracks.

The tendency of the oil cake to absorb liquids and soften is reduced while the gel melting temperature is increased. In applications, agar is usually mixed with other vegetable gels such as guar gum and locust bean gum.

9. Application in meat products
Agar is used in meat processing, can effectively maintain the flavor of the product. Agar is used in sausages, smoked or filleted meat products, where it significantly protects the colloid to prevent loss of flavor.

For this purpose, cooked ham can also be covered with a solution containing agar and ascorbic acid, after packaging, the agar-treated meat products than untreated and only with ascorbic acid alone to maintain the original flavor.

10.Other food applications
Agar in the brewing industry, as beer, soy sauce and vinegar clarifying agent to accelerate and improve the clarification of the product; agar with its unique physical and chemical properties, such as high melting point, not easy to mold characteristics, as a substitute for gelatin, alternative to gelatin in all aspects of use.