The most important processed seaweed products in Indonesia are the hydrocolloids agar and carrageenan. The following chapter gives an overview about the raw material which is used for the agar production, the processing technologies of agar and their applications.
Raw Materials For Agar Productions In Indonesia
Agar is a natural hydrocolloid extracted from seaweeds all belonging to the Rhodophyceae class (red algae). Two genera, Gelidium and Gracilaria, account for most of the raw material used for the extraction of agar.
Extraction of Gelidium species gives the higher quality agar measured as gel strength. However, nearly all Gelidium used for commercial agar extraction still comes from natural resources in the wild, resulting in a certain limitation of supply. Gelidium is a small, slow growing plant and while efforts to cultivate it in tanks and ponds have been biologically successful, it has so far not been proved to be economical feasible.
In the past, Gracilaria species were once considered unsuitable for agar production because the quality of the agar was considered inferior due to lower gel strength. But in the 1950s, it was found that pre-treatment of the seaweed with alkali before extraction although lowering the yield gave a good quality agar with higher gel strength.
This allowed expansion of the agar industry, previously limited by the supply of Gelidium available, and led to the harvesting of a variety of wild species of Gracilaria in countries such as Indonesia.
Cultivation methods were then developed, both in ponds and in the open waters of protected bays. Today the supply of Gracilaria in Indonesia is mainly cultivated. The country has become one of the largest and best positioned supplier of agar to the food industry worldwide.
Current Processing Technologi Of Agar
The basic principle in all processes for the production of agar is simply an extraction of the agar from the seaweed 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.
The agar is extracted by heating in water for several hours. During this process the 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 °C 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 °C for 2–4 hours) as this is faster and gives higher yields. Gracilaria is usually just extracted with water at 95–100 °C 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.
Aplications Of Agar
The name “agar” or “agar-agar” originates in Indonesia. The widespread use of agar is caused by its ability to form gels, and the unique properties of these gels. Agar dissolves in boiling water and when cooled it forms a gel between 32 and 43 °C, depending on the seaweed source of the agar. In contrast to gelatin gels, that melt around 37 °C, agar gels do not melt until heated to 85 °C or higher. In food applications, this means there is no requirement to keep them refrigerated in hot climates. This large difference between the temperature at which a gel is formed and the temperature at which it melts is unusual, and unique to agar. Many of its applications take advantage of this difference.
About 90 % of the agar produced is intended for food applications, with the remaining 10 % being used for bacteriological and other biotechnology applications. Agar has a preferential status all over the world: It is derived from a vegetable source, easy to use without any knowledge in chemistry needed and most importantly, agar has never received any negative comments. In addition, agar is tasteless and does not interfere with the flavors of foodstuffs, in contrast to some other gelling agents.
In the baked goods industry, the ability of agar gels to withstand high temperatures means agar can be used as a stabilizer and thickener in pie fillings, icings and meringues. Cakes, buns, etc., are often pre-packed in various kinds of modern wrapping materials which often stick to the product, especially in hot weather. By reducing the quantity of water and adding some agar, a more stable, smoother, non-stick icing for the product is obtained. For the same reasons, one of the larger application for agar in North America is on donuts. Nowadays, agar from Gracilaria are often preferred in confectionery with a very high sugar content, such as fruit candies.
In Asian countries, agar is a traditional and popular component of jellies. Probably, this has its origin in the early practice of simply boiling seaweed, straining it, adding flavors to the liquid before it cooled and formed a jelly. It is believed that this was the way agar was invented as a gelling agent already several hundred years ago. A popular Japanese sweet dish is mitsumame It consists simply of cubes of agar gel containing fruit and added colors. It can be canned and sterilized without the cubes melting.
Agar is also used in gelled meat and fish products, and is preferred to gelatin because of its higher melting temperature and gel strength. It also improves the texture of dairy products like cream cheese and is often used in yoghurt, especially in North America.
Unlike starch, agar is not readily digested and therefore adds little calorific value to food. In addition, it is described as a high fiber additive. Agar is often used in vegetarian foods such as meat substitutes.
In the pharmaceutical industry, agar is used as a growth substrate to obtain clones or copies of particular plants in nurseries. Bacteriological agar is used in testing for the presence of bacteria. It is specially purified to ensure that it does not contain anything that might modify bacterial growth. The highest quality agar and its derivative agarose is used for biotechnological applications of DNA research and gel electrophoresis and diagnostic purposes.