Agar Agar E406 Production
The basic principle in all processes for the production of Agar agar is simply an extraction of the agar from the seaweed algae Gelidium and Gracilaria after it has been cleaned and washed. This step is necessary to remove any foreign material such as sand, salts, sticks and any debris which may appear naturally with the seaweed.
Agar agar is extracted by heating in water for several hours. During this process Agar agar dissolves in the water. The mixture is then filtered to remove the residual seaweed. The hot filtrate is cooled and forms a gel which contains about one percent agar. The gel is broken into pieces and washed to remove all soluble salts, and, if necessary, it can be bleached to reduce the color. After this step, water is removed from the gel, either by a freeze-thaw process or nowadays more likely by squeezing it under pressure. Remaining water can then be removed by drying. The final step is to mill the agar to a suitable and uniform particle size.
There are some differences in the treatment of the seaweed prior to extraction, depending on the type of seaweed. With Gelidium the process is simply washing with plain water or sometimes with a little acid to facilitate extraction. Whereas Gracilaria must be treated with alkali before extraction to obtain the optimal gel strength. For the alkali treatment, the seaweed is heated in 2–5 percent sodium hydroxide at 85–90 ¢XC typically for one hour. After the removal of the alkali, the seaweed is washed with water, and sometimes with weak acid to neutralize any residual alkali.
For the hot-water extraction, Gelidium is more resistant. The extraction of this type of seaweed takes often place under pressure (105–110 ¢XC for 2–4 hours) as this is faster and gives higher yields. Gracilaria is usually just extracted with water at 95–100 ¢XC for 2–4 hours. The hot extract is given a coarse filtration to remove the seaweed residue, filter aid is added and the extract is passed through a filter press equipped with a fine filter cloth to ensure removal of any insoluble products.