The turning seaweed production offers a natural beginning of applicable substances used in a assortment of industries responsible for the production of nutrient, carnal feed-stock, fertiliser, biofuel and cosmetics. Seaweed is harvested either from its natural home ground ( wild ) or from cultivated harvests. Because of the quickly spread outing demand of seaweed merchandises which exceed natural available resources, cultivation has increased dramatically over the old ages. Seaweeds are classified into three chief groups of macro-algae viz. : Rhodophyceae ( ruddy ) , Phaeophyceae ( brown ) and Chlorophyceae ( green ) . Both brown and ruddy algae are straight processed into comestible merchandises and are used for the extraction of the polyoses alginate ( brown ) , carrageenin and agar ( ruddy ) .
Fig. 1 Images of the chief group of macro-algae: Chlorophyceae ( green ) , Rhodophyceae ( ruddy ) , Phaeophyceae ( brown ) .
1. Cultivation of ruddy algae in the seaweed industry:
1.1 Methods for cultivation of algae
Two general processs are used for the growing of seaweed, one is by vegetive method and the other is by separate generative rhythm affecting alternation of coevals. The vegetive method is largely used for the production of hydrocolloids ( agar and carrageenin ) while the chief seaweeds used as nutrients must be taken through the alternation of coevals for their cultivation. The vegetive method is merely the straightforward cultivation of seaweed placed in an environment that will prolong their growing, depending on salt, foods, visible radiation, temperature and motion of the H2O. To obtain optimum growing, seaweed is attached to ropes or cyberspaces that are tied to a drifting wooden frame. Cultivation affecting a generative rhythm, with alternation of coevalss, is necessary for many seaweeds, particularly the Phaeophyceae algae. For these, new workss can non be grown by taking film editings from mature 1s. The sporophyte is what is harvested as seaweed. To turn a new sporophyte it is necessary to travel through a sexual stage affecting the gametophytes. The mature sporophyte releases spores that develops and turn into microscopic gametophytes.
The gametophytes become fertile, release sperm and eggs that join to organize embryologic sporophytes. These easy develop into the big sporophytes that are harvested ( 1 ) .
Two general species of seaweed, Gelidium and Gracilaria, history for most of the natural stuff used for the extraction of agar.
Gelidium: Extraction of Gelidium gives the higher quality agar ( measured by the gel strength ) . All Gelidium used for commercial agar extraction comes from natural resources, chiefly from France, Indonesia, the Republic of Korea, Mexico, Morocco, Portugal and Spain. Gelidium is a little, slow growth works and while attempts to cultivate it in tanks/ponds have been biologically successful, it has by and large proved to be uneconomic.
Gracilaria: Gracilaria species were one time considered unsuitable for agar production because the quality of the agar was hapless ( gel strength excessively low ) . In the 1950s, it was found that pre-treatment of the seaweed with base before extraction lowered the output but gave a good quality agar. This allowed enlargement of the agar industry and led to the harvest home of a assortment of wild species of Gracilaria in states such as Argentina, Chile, Indonesia and Namibia. Due to overharvesting of the wild harvest cultivation methods were developed, both in pools and in the unfastened Waterss of protected bays. These methods have spread to other states, such as China, the Republic of Korea, Indonesia, Namibia, the Philippines and Viet Nam, normally utilizing species of Gracilaria native to each peculiar state. Gracilaria species can be grown in both cold and warm Waterss.
1.3 Harvesting methods for wild agarophytes
Industrial reaping techniques for agarophytes vary, depending on fortunes, but they can be classified as follows:
– assemblage of seaweeds washed to the shore ;
– assemblage seaweeds by cutting or rooting them
out from their beds ;
Gathering of seaweeds washed to the shore. In some states these seaweeds called “ argazos ” , “ arribazon ” or “ beach wash ” . These are dead seaweeds that, after finishing their biological rhythm, are separated by seasonal storms. They are gathered by manus or by mechanical agencies from the seashore or by tight air ousters from boats that gather the seaweeds settled in pits at deepnesss of about 25 meters ( “ Wellss ” ) . To avoid agitation, the seaweed should be gathered shortly after it has separated from its fastener.
Gathering seaweeds by cutting or rooting them out from their beds. This work is done with profligates or grabs handled from boats or by frogmans. Gelidium normally occurs on bouldery beds, Gracilaria on flaxen 1s. In general it is executable to run with frogmans in deepnesss between 3 and 20 meters.
Cultivation. Nowadays the demand for greater measures of agarophytes has brought about the debut of cultivation of Gracilaria harvests. However this cultivation has had merely limited success and there are some facets to be solved before it can be by and large adopted. At the present clip, cultivation for industrial intents is undertaken in the People ‘s Republic of China, its Taiwan Province and it is now being initiated in Chile.
1.4 Post-harvest intervention
The saving of seaweeds, between the clip of reaping and their existent usage by the agar maker, is really of import. To construct a seaweed processing mill, which consumes seaweeds at the rate they are harvested, is non practical. Large graduated table agar industry makes it necessary to hold available measures of agarophytes stabilized in such a manner that they can be carried long distances, at the least possible cost, and stored for a long clip before processing.
The first measure is saving through desiccation, to avoid agitation that first destroys the agar and so the seaweed. The 2nd measure is pressing the weed with a hydraulic imperativeness in bales of about 60 kilograms, to cut down the volume and return transit and storage costs. Dehydration must be sufficient to vouch the seaweed ‘s saving, otherwise an anaerobiotic agitation will happen inside the bales doing high temperatures and even carbonisation of the seaweeds during storage in warehouses. In general, the wet content is best reduced to about 20 % by natural or unreal drying. In the instance of Gracilaria the job is more hard to work out. The enzymatic hydrolysis of its agar occurs spontaneously even at comparatively low wet contents, but at variable rates depending on the Gracilaria species and its beginning. Gracilaria harvested in India, Sri Lanka, Venezuela, Brazil, and by and large in warm Waterss, has an agar ( agarose ) less immune to enzymatic hydrolysis than the Chilean Gracilaria which is the most stable.
However, the stableness of agar contained in Gracilaria is less than that of Gelidium ; Gelidium agar can be preserved in seaweeds indefinitely provided they have been good treated.
Hydrolysis of agar contained in Gracilaria can be due to endogenous enzymes or to the growing of Bacillus Cereus ( 2 ) .
2. Production procedure of Agar:
2.1 Agar production methods
A short and simplified description of the extraction of agar from seaweeds is that the seaweed is washed to take foreign affair and so heated with H2O for several hours. The agar dissolves in the H2O and the mixture is filtered to take the residuary seaweed. The hot filtrate is cooled and forms a gel ( jelly ) which contains about 1 per centum agar. The gel is broken into pieces, and sometimes washed to take soluble salts, and, if necessary, it can be treated with bleach to cut down the coloring material. Then the H2O is removed from the gel, either by a freeze-thaw procedure or by squashing it out utilizing force per unit area. After this intervention, the staying H2O is removed by drying in a hot-air oven. The merchandise is so milled to a suited and unvarying atom size. There are some differences in the intervention of the seaweed prior to extraction, depending on the agarophytes used. Gelidium is merely washed to take sand, salts, shells and other foreign affair and is so placed in armored combat vehicles for extraction with hot H2O. Gracilaria is besides washed, but it must be treated with base before extraction ; this alkalic pre-treatment causes a chemical alteration in the agar from Gracilaria, ensuing in an agar with an increased gel strength. Without this alkalic pre-treatment, most Gracilaria species yield an agar with a gel strength that is excessively low for commercial usage ( 3 ) .
2.2 Forms of Agar for industrial utilizations:
2.2.1 Agar strips
Agar for usage in nutrient is sold in two signifiers: strip agar and agar pulverization. The pulverization is produced by the method antecedently described. Agar strip, sometimes called natural agar, is produced on a little graduated table in China, Japan and the Republic of Korea by the old, traditional method. Gelidium must be used ; it was the lone natural stuff used before the Second World War. It is boiled for several hours in H2O, acidified by the add-on of either acetum or dilute mineral acid. The hot infusion is filtered through cotton fabrics, so poured into wooden trays to chill and organize a gel. The gel is extruded to bring forth spaghetti-type strips about 30 centimeters long. The strips are placed outside at dark to freezing and allowed to dissolve in the twenty-four hours, so H2O is released and runs off, go forthing a more concentrated gel. This procedure can be repeated, or modern infrigidation can be substituted. The strips are dried in the Sun, which besides bleaches the strips. Strips are assembled into packages. Anterior soakage makes them easier to fade out in boiling H2O.
2.2.2 Bacteriological agar
This can merely be made from species of Gelidium because the ensuing agar has a low gelling temperature ( 34-36A°C ) that allows the add-on of other stuffs to the agar with a minimal hazard of heat harm. Gracilaria gives agar that gel at 41A°C or higher. bacteriological agars must non incorporate anything that might suppress the growing of bacteriums, such as hint metals, soluble saccharides or proteins, nor should they incorporate any bacterial spores. They must non interact with any stuffs that must be added as foods for the bacteriums under survey. The gels must be strong and have good lucidity. Manufacturers of bacteriological agar maintain all processing inside informations confidential. However, late Kim et Al. ( 2000 ) published inside informations [ in Korean ] of a pilot-scale readying that they claim gave a merchandise that is superior to commercial bacteriological agar.
Agar can be divided into two chief constituents: agarose and agaropectin. Agarose is the gelling constituent ; agaropectin has merely a low gelling ability. Agarose is a additive polymer, made up of the monomer agarobiose. Agarobiose is a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose. Agaropectin is a heterogenous mixture of smaller molecules that occur in lesser sums. Their constructions are similar but somewhat branched, sulfated, and may hold methyl and pyruvic acid ketal substituents.
Fig. 2 Chemical construction of agarobiose ( monomer ) and agarose ( polymer ) .
Some agars, particularly those extracted from Gracilaria, can be used in confectionery with a really high sugar content, such as fruit confects. These agars are said to be “ sugar reactive ” because the sugar ( sucrose ) increases the strength of the gel. Because agar is tasteless, it does non interfere with the spirits of groceries ; this is in contrast to some of its competitory gums that require the add-on of Ca or K salts to organize gels. In Asiatic states, it is a popular constituent of gelatins ; this has its beginning in the early pattern of boiling seaweed, striving it and adding spirits to the liquid before it cooled and formed a jelly. A popular Nipponese sweet dish is mitsumame ; this consists of regular hexahedrons of agar gel incorporating fruit and added colorss. It can be canned and sterilized without the regular hexahedron thaw.
Fig 4. The Nipponese sweet dish ‘mitsumame ‘ .
Agar is besides used in gelled meat and fish merchandises, and is preferred to gelatin because of its higher thaw temperature and gel strength.
In combination with other gums, agar has been used to stabilise sherberts and ices. It improves the texture of dairy merchandises like pick cheese and yogurt. It has been used to clear up vinos, particularly plum vino, which is hard to clear up by traditional methods. Unlike amylum, agar is non readily digested and so adds small calorific value to nutrient. It is used in vegetarian nutrients such as meat replacements.
3.3 Other utilizations
In the pharmaceutical industry agar has been used for many old ages as a smooth laxative. In orchid baby’s rooms, agar gels incorporating appropriate foods are used as the growing substrate to obtain ringers or transcripts of peculiar workss.
Fig 5. Agar used as a growing substrate.
The gel web of agarose contains dual spirals formed from left-handed threefold spirals ( 4 ) . These dual spirals are stabilized by the presence of H2O molecules bound inside the dual coiling pit. Exterior hydroxyl groups allow collection of up to 10,000 of these spirals to organize suprafibers.
3. Applications of Agar-based merchandises:
3.1 Agar utilizations
The utilizations of agar Centre around its ability to organize gels, and the alone belongingss of these gels. Agar dissolves in boiling H2O and when cooled it forms a gel between 32A° and 43A°C, depending on the seaweed beginning of the agar ( 5 ) . In contrast to gelatin gels, that melt around 37A°C, agar gels do non run until heated to 85A°C or higher.
Fig. 3 Example of agar-agar used as a gel in nutrient.
In nutrient applications, this means there is no demand to maintain them refrigerated in hot climes. At the same clip, they have a oral cavity experience different from gelatin since they do non run or fade out in the oral cavity, as gelatin does. This big difference between the temperature at which a gel is formed and the temperature at which it melts is unusual, and alone to agar. Many of its applications take advantage of this difference.
About 90 per centum of the agar produced is for nutrient applications, the staying 10 per centum being for bacteriological and other biotechnology utilizations. In the adust goods industry, the ability of agar gels to defy high temperatures means agar can be used as a stabilizer and thickening in pie fillings, frosts and meringues. Cakes, buttocks, etc. , are frequently pre-packed in assorted sorts of modern wrapper stuffs and frequently stick to them, particularly in hot conditions ; by cut downing the measure of H2O and adding some agar, a more stable, smoother, non-stick frost is obtained.
Meristems – the portion of the works with actively spliting cells, normally the root tips – are grown in the gel until there has been sufficient root development and growing for them to be transplanted. An advantage of this system is that the workss can be cultured in a unfertile environment.
3.4 Microbiological agar
Bacteriological agar is used in proving for the presence of bacteriums. It is specially purified to guarantee that it does non incorporate anything that might modify bacterial growing. It is hence more expensive, often at least twice the monetary value of nutrient class agar. A hot agar solution ( 1-1.5 per centum ) is prepared and as it cools, foods or other chemicals specific for the type of bacteriums being tested are added. When the solution has cooled below its gel point, the sample suspected of incorporating bacterium is spread on the surface of the gel, which is so covered and stored at a temperature suited for bacterial growing. The agar gel should be every bit clear as possible so that any bacterial growing can be easy seen.
Fig 6. A petri dish with bacterial settlements on a agar-based growing medium.