| Provisco AG | |
| Waldkircherstrasse 7 | |
| CH-9213 Hauptwil, Switzerland | |
| Phone: | +41 71 422 66 55 |
| Fax: | +41 71 422 66 56 |
Agar, Agar-Agar
Sources and Extraction
Agar is a structuring component of the membrane of the red seaweed (rhodophyceae). The key resources are species of gelidium, gracilaria and pterocladia. The most important production countries are Japan, USA (California) and Spain, where it grows on the rocky coasts. The red seaweed is gathered and extracted with water at a pH-value of 5 – 6 and a temperature of 100 – 130° C under pressure. The extract is purified by filtration or centrifugation and then bleached with calcium hypochlorit. To isolate the agars, the extract is being freezed, and the colloidal residue remaining after thawing is dried. Recently, the water is being crushed out with a press and the remaining water removed by dehydration. The annual production is estimated at about 5000 tons.
Properties
Appearance
Unground agar consists of thin stripes of flakes, ground agar is a white to slightly yellowish powder.
Composition
Agar is a heterogeneous polysaccharide with the components D-galactose and 3,6-anhydro-L-galactose. In addition to the predominant agarose which is responsible for the gelification, a minor quantity of the non-gelling agaropectin is present, which is a slightly acidic polysaccharide also containing groups of sulfate ester, glucuronic acid and pyruvic acid. Agarose is a neutral, linear galactan. The D-galactose and 3,6-anhydro-L-galactose components are alternatingly linked to each other by a-(1-3) and b-(1-4) bonds. Due to the high content of anhydrogalactose and the absence of sulfate ester groups requiring an enforced hydrophobic character, agar is a very good gelling agent independent from cations.
Solubility
Agar is insoluble in cold water. Complete solution occurs only at temperatures above 80 °C. By cooling down the solution to about 35 °C, a thermo-reversible gel is formed which remelts when heated to above 85° C. As agar is a neutral hydrocolloid, its solubility is not influenced by electrolyte additives. Agar is completely resistent to the enzymes applied in the food technology area.
Agar belongs to the group of polysaccharides with the most distinct gel forming capacity. (concentration limit at about 0.5 %). Agar proves stable against heat treatment in the neutral media; longer influence of heat at lower pH values, however, causes hydrolytic degradation. Agar gels stand out for their high gel strength and gel firmness. The gels however show strong tendency to syneresis and have little transparency. Together with carob bean gum, agar shows a strong synergistic effect. Synergism is caused by a reaction between the double-helix segments of the agar and the even carob bean gum segments carrying no galactose side chains. This synergism results in an improvement of the gelling properties of agar and reduces the tendency to syneresis.
Application properties
The application of agar is premarily based on its gelling properties. Due to the heat resistance of its gels, agar has proved to be suited especially for tinned meat, fish and poultry, but also for the pastries and confectionery industry. Because of the solubility of agar in saturated sugar solution, the independence of the gelling temperature from the sugar concentration and the low stickiness of the gels, agar is particularly suited for sugar coatings and glosses. Agar is further applied in the confectionery industry to produce jelly sweets and to stabilise the texture of ice-creams. However, the relatively high price of agar is a disadvantage for its application in the food industry. In addition, agar is also widely used for the production of culture mediums in the microbiology.
Toxicologic Evaluation
Since former times seaweed serves as ingredient for human nutrition. Beside the large experience with the use of agar in animal feed, clinical experiences with the application as laxative are on hand. Therefore, no sanitary objections exist despite the lack of substancial toxicologic tests. A limitation of the allowed daily intake (ADI) thus did not prove necessary.