What is the right spelling for this agar?

What is the right spelling for this agar?

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I could not spell the agar [gonoline-uroline] which I heard yesterday. My spelling is so wrong that I could not find it in Google.

What is the right spelling for this agar?

The first word is ok, there is agar called Gonoline, the second one is probably Euroline and there is an agar with this word too (Liver IgG Euroline).

I've found both of them on the Italian site, probably the are not one, but two agars.

Looking at your two questions together, I think you mean gonoline media, followed by blood agar. To be honest, I feel like this question would be off topic. You may be referring to a specific blood agar, like Chocolate agar, but that would be wild speculation.

Gonoline media is often used for Neisseriaceae, so perhaps you are specifically looking at Gonorrhea?


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While the beans are cooling and drying, melt the butter in a saute pan over medium heat.

Place the thinly sliced shallots in a medium bowl and pour buttermilk over to coat.

Heat the rum in a small skillet over medium until reduce by half.

While the pork is resting, heat a large, heavy-bottomed pan over medium -high heat.

Finish the sauce by putting the roasting pan on the stovetop over medium -high heat.

The medium pitch expresses warmth, emotion, and the heart qualities.

They vary greatly in size, being sometimes so small as to seem mere points of light with medium -power objectives.

At present this medium is paper money depreciated, as in the case of the Reichsbank notes, by nearly 30 per cent.

"Say yes quickly," he cried, and the strength of his will and passion vibrated to her through the medium he had established.

And a rampant ache in my head, seconded by a medium -sized gash in the scalp, didn't make for an access of optimism at that moment.

Differences between Agar and Gelatin

We have categorized the differences into several distinct factors, starting from their composition to the health benefits. Which brings us to our next big question, where exactly does agar agar and gelatin come from?


Source of Agar agar

Agar agar comes from the cell wall of a species of seaweed (red algae) mostly found in the Pacific and coastal region of California. You can find them in both kitchens and laboratories alike. It’s considered at least 7-8 times stronger than gelatin due to having a plant-based origin.

Source of Gelatin

Gelatin is the non-vegetarian alternative of agar agar. Manufacturers use the acidic and alkaline process to derive gelatin from the collagens of the skins, tendons, and bones of animals. Recently another type of gelatin has earned some popularity which is derived from fish and insects.


Composition of Agar agar

Agar consists of two types of carbohydrates, namely Agarose (70-75%) and Agaropectin (30-25%). It tends to melt at 85 °C (358 K).

The composition of agar agar plays a big role in its property of easy melting and gel stability. It can be ground into a fine powder. So you can commonly find them in the market in the form of powders and strips. It’s white and quite translucent.

Composition of Gelatin

Peptides and proteins are the main constituents of gelatin. They are obtained from the collagen of animal’s bones and other connective tissue through a series of chemical reactions, known as partial electrolysis.

Due to its composition, it melts in any liquid with a temperature of 35° to 40° C. It loses its strength upon exposure to a temperature of more than 100° C (373.15° K).

The gelatin found in the market is much more granular than agar agar. You will mostly find them in packs of powders or sheets. It’s colorless, odorless, and translucent

Uses of Gelatin

Gelatin is used to make various sorts of foods. Common examples are marshmallows, marmalade’s, gummy bears, trifles, frozen desserts, sponge cakes, and other gelatinous desserts. Gelatin is also used to make confections such as jelly toppings for cakes.

Large scaled dairy product factories also use gelatin to prepare products such as margarine, mayonnaise, and yogurt. Technical uses of gelatin include the manufacture of cosmetics, photo films, sandpaper, and capsules of medicines.

Uses of Agar

Since both gelatin and agar agar are gelling agents, therefore most of their uses for culinary purposes are common to each other.

Similar to gelatin, agar agar can be used to make semi-solid desserts such as jellies, custards, puddings, no-bake cheesecakes, etc. Popular Asian desserts such as ‘Wagashi’ (traditional Japanese dessert made from plant-based ingredients) are made with agar agar.

You can use Agar agar to make creamy fillings for sponge cakes or pies or use it as a thickener for gravies of desserts. They are also used in the fields of microbiology, dentistry, etc. Many people use it as a laxative as well.

Did you know?

If you think you see a connection between "inoculate" and "ocular" ("of or relating to the eye"), you are not mistaken - both words look back to "oculus," the Latin word for "eye." But what does the eye have to do with inoculation? Our answer lies in the original use in English of "inoculate" in Middle English: "to insert a bud in a plant." Latin oculus was sometimes applied to things that were seen to resemble eyes, and one such thing was the bud of a plant. "Inoculate" was later applied to other forms of engrafting or implanting, including the introduction of vaccines as a preventative against disease.

Serratia Marcescens as a Tracer Organism

Serratia marcescens was used as a tracer organism for many years until its pathogenicity was finally revealed. In the First World War, where controlled medical experiments were often carried out on soldiers, the mechanisms of bacterial infection via the mouth and gastrointestinal system could be studied thanks to the distinctive red coloration provided by S. marcescens. Medical researchers would place S. marcescens on the gums before dental surgery to see whether bacteria could enter the bloodstream, for example. Most famously, the U.S. military used Serratia marcescens to show the results of possible biological warfare and released large numbers of Serratia into subway systems, government and military facilities, and entire urban populations. This led to infection and a small number of S. marcescens infection-related deaths. Press publicity of the ensuing court cases that began in the late 1960s reached global audiences.

Additional Safety Considerations(6)

  • When stirring the broth solution, one should take special note in beginning the stir scale at a low setting and adding more speed from there.
  • When heating the broth, make sure to cover the flask in such a manner that will not lend itself to boiling over, but to avoid spillage.
  • When pouring the broth, make sure to fill the Petri dish without burning oneself. In addition it is important in this process to make sure that the Petri dish is covered immediately to allow the substance to cool proportionately.
  • Once the Petri dishes have been exposed or inoculated, students should not re-open them.

The streak plate method requires the number of organisms in the inoculums be reduced. The procedure includes a dilution technique which requires spreading a loopful of culture over the agar plate surface.

This is to make sure that the individual cells fall apart on the agar medium surface so as separation of the different species takes place. This procedure is also called rapid qualitative isolation method. (2, 3, and 4)

Picture 3: Inoculating a plate using a streak plate technique.

Image Source:

Picture 4: A pure bacterial isolate using the streak plate technique.

Image Source:

Picture 5: The actual result of a streak plate technique.


Side Effects

Children: Agar is POSSIBLY SAFE when given by mouth to infants with neonatal jaundice for up to 7 days.

Pregnancy and breast-feeding: There isn't enough reliable information to know if agar is safe to use when pregnant or breast-feeding. Stay on the safe side and avoid use.

Bowel blockage (obstruction): Agar might make bowel obstruction worse, especially if it isn't taken with enough water or other liquid. Get medical advice before taking agar if you have a bowel obstruction.

Trouble swallowing: Agar might swell up and block the eating tube (esophagus) if it isn't taken with enough water or other liquid. This can be especially dangerous for someone who has trouble swallowing. Get medical advice before taking agar if you have a swallowing problem.

Starch Hydrolysis Test – Principle, Procedure, Uses and Interpretation

Many bacteria produce extracellular enzymes used to catalyze chemical reactions outside of the cell. In this manner, nutrient sources, such as starch, that are too large to be absorbed through the cell membrane can be broken down into smaller molecules and transported into the cell via diffusion.

In the starch hydrolysis test, the test bacteria are grown on agar plates containing starch. If the bacteria have the ability to hydrolyze starch, it does so in the medium, particularly in the areas surrounding their growth while the rest of the area of the plate still contain non-hydrolysed starch. Since no color change occurs in the medium when organisms hydrolyze starch, iodine solution is added as an indicator to the plate after incubation. While the non-hydrolysed starch forms dark blue color with iodine, its hydrolyzed end products do not acquire such dark blue color with iodine.

Consequently, transparent clear zones are formed around the colonies that hydrolyze starch while the rest of the plate show a dark blue coloration as iodine forms the colored complex with starch.

Starch agar is a simple nutritive medium with starch added. Beef extract and pancreatic digest of gelatin provide nitrogen, vitamins, carbon and amino acids. Agar is the solidifying agent and starch is the carbohydrate.


Peptic digest of animal tissue 5.000, Sodium chloride 5.000, Yeast extract 1.500, Beef extract 1.500 Starch, soluble 2.000 Agar 15.000 Final pH ( at 25°C) 7.4±0.2

What is the right spelling for this agar? - Biology

by Rafael Armisen and Fernando Galatas
Hispanagar, S.A., Poligono Industrial de Villalonquejar
Calle López Bravo "A", 09080 Burgos, Spain

According to the US Pharmacopeia, agar can be defined as a hydrophilic colloid extracted from certain seaweeds of the Rhodophyceae class. It is insoluble in cold water but soluble in boiling water. A 1.5% solution is clear and when it is cooled to 34-43°C it forms a firm gel which does not melt again below 85°C. It is a mixture of polysaccharides whose basic monomer is galactose. These polysaccharides can be sulphated in very variable degrees but to a lesser degree than in carrageenan. For this reason the ash content is below those of carrageenan, furcelleran (Danish agar) and others. A 5% maximum ash content is acceptable for agar although it is normally maintained between 2.5-4%.

Agar is the phycocolloid of most ancient origin. In Japan, agar is considered to have been discovered by Minoya Tarozaemon in 1658 and a monument is Shimizu-mura commemorates the first time it was manufactured. Originally, and even in the present times, it was made and sold as an extract in solution (hot) or in gel form (cold), to be used promptly in areas near the factories the product was then known as tokoroten. Its industrialization as a dry and stable product started at the beginning of the 18th century and it has since been called kanten. The word "agar-agar", however, has a Malayan origin and agar is the most commonly accepted term, although in French- and Portuguese-speaking countries it is also called gelosa.

A Japanese legend is told about the first preparation of agar:

Agar production by modern techniques of industrial freezing was initiated in California by Matsuoka who registered his patents in 1921 and 1922 in the United States. The present manufacturing method by freezing is the classic one and derives from the American one that was developed in California during the years prior to World War II by H.H. Selby and C.K. Tseng (Selby, 1954 Selby and Wynne, 1973 Tseng, 1946). This work was supported by the American Government which wanted the country to be self sufficient in its strategic needs, especially in regard to bacteriological culture media.

Apart from the above American production, practically the only producer of this phycocolloid until World War II was the Japanese industry which has a very traditional industrial structure based on numerous small factories (about 400 factories operated simultaneously). These factories were family operated, producing a non-standardized quality, and had a high employment rate as production was not mechanized. For this reason, and in spite of the later installation of some factories of a medium to small size, only in recent times has Japan operated modern industrial plants.

During the second world war the shortage of available agar acted as an incentive for those countries with coastal resources of Gelidium sesquipedale , which is very similar to the Gelidium pacificum used by the Japanese industry. So in Portugal, Loureiro started the agar industry in Oporto while at the same time J. Mejias and F. Cabrero, in Spain, commenced the studies which led to the establishment of the important Iberian agar industry. Other European countries which did not have agarophyte seaweeds tried to prepare agar substitutes from other seaweed extracts (see Appendix).

Different seaweeds used as the raw material in agar production have given rise to products with differences in their behaviour, although they can all be included in the general definition of agar. For this reason, when agar is mentioned, it is customary to indicate its original raw material as this can affect its applications (Figure 1). Hence we talk about Gelidium agar, Gracilaria agar, Pterocladia agar, etc. To describe the product more accurately, it is usual to mention the origin of the seaweeds, since Gracilaria agar from Chile has different properties from Gracilaria agar from Argentina and Gelidium agar from Spain differs from Gelidium agar from Mexico.

Originally Gelidium agar constituted what we consider genuine agar, assigning the term agaroids to the products extracted from other seaweeds. Although these agaroids do not have the same properties as Gelidium agar, they can be used as substitutes under certain conditions. After World War II, the Japanese industry was forced to use increasing quantities of raw materials other than the traditional Gelidium pacificum or Gelidium amansii due to the growing demand of the international food industry.

An increase in the agar gel strength was obtained through improvements in the industrial process during the fifties, and the differences between the genuine Gelidium agar and the agaroids then available became clearer. The gel strength increased from 400 g/cm 2 (the maximum for natural agar produced by the cottage industry) to 750 g/cm 2 or more for the agar produced by industrial methods. The gel strength data refer to the Nikan-Sui method which replaced the primitive Kobe method used in the past. The Nikan method is more precise and easier to reproduce. A short description of the method is included in the section on "Properties".

The Japanese discovery of the strong alkaline methods for agar extraction (see section on "Manufacturing Processes") meant an increase of the Gracilaria agar gel strength with the subsequent utilization of seaweeds imported from South Africa to increase the raw material available.

Nowadays the world agar industry basically uses the following seaweeds:

(1) Different species of Gelidium harvested mainly in Spain, Portugal, Morocco, Japan, Korea, Mexico, France, USA, People's Republic of China, Chile and South Africa.

(2) Gracilaria of different species harvested in Chile, Argentina, South Africa, Japan, Brazil, Peru, Indonesia, Philippines, People's Republic of China including Taiwan Province, India and Sri Lanka.

(3) Pterocladia capillace from Azores (Portugal) and Pterocladia lucida from New Zealand.

(4) Gelidiella from Egypt, Madagascar, India, etc.

Figure 2 shows Gracilaria and Gelidium

Other seaweeds are utilized as well, such as Ahnpheltia plicata from North Japan and the Sakhalin Islands as well as Acanthopheltis japonica , Ceramiun hypnaeordes and Ceranium boydenii (Levring, Hoppe and Schmid, 1969).

The geographical distribution of agarophytes is very wide and is shown in Figure 3. Main areas are located indicating the most important classes and species. The size of the coloured areas relate to the extent of the gathering area, not the quantity of seaweeds gathered.

There are areas in which different kinds of agarophytes are gathered. This is the case in Chile, a country of exceptional resources of algae. In 1984, 6 126 tons of dried Gracilaria were gathered from its very long sea coast and exported to Japan, as well as another 5 500 tons that were used by the local industry. Simultaneously, in rocky areas, sandwiched between sandy areas where Gracilaria grows, 304 tons of dried Gelidium were gathered and exported to Japan. In countries such as India and Sri Lanka, Gracilaria and Gelidiella grow together in areas relatively close to each other. Generally Gelidium resources are being exploited quite heavily and so are those of good quality Gracilaria . At present the utilization of Gelidiella is being developed.

It is difficult to evaluate the present collection of agarophytes all over the world but since Japan has been, for a long time, the sole importing country of these seaweeds (basically needed to maintain production levels of the agar industry), Japanese statistics (Figure 4a) are very valuable in giving a true view of the situation. Note that in the Japanese statistics, Gelidium seaweeds are separated from other seaweeds. In 1984, Japan imported 678 tons of Gelidium seaweeds and 9 462 tons of "other agarophytes", mainly Gracilaria and Gelidiella . However it seems that Gelidiella is included with Gelidium in some cases, probably because Gelidiella seaweeds have been called Gelidium rigidum by some phycologists in spite of the fact that they are generally considered to be of a different class. As far as agar manufacturers are concerned, they are not Gelidium since the product obtained from then is completely different from the real Gelidium agar. The Gelidium lots assigned to the Philippines (3 tonnes) and to Indonesia (62 tonnes) are probably Gelidiella . Also Gelidium from Brazil is most probably Pterocladia which can be confused with Gelidium (no Gelidium is harvested in Brazil while some quantities of Pterocladia are).


Industrial harvesting techniques for agarophytes vary, depending on circumstances, but they can be classified as follows:

(1) gathering of seaweeds washed to the shore

(2) gathering seaweeds by cutting or rooting them out from their beds

(3) cultivation.

Figure 4a Agarophyte seaweeds imported by Japan 1984

Figure 4b Agar production in different countries indicating the seaweeds used

People's Republic of China

Gathering of seaweeds washed to the shore. In some countries these seaweeds called "argazos", "arribazon" or "beach wash". These are dead seaweeds that, after completing their biological cycle, are separated by seasonal storms. They are gathered by hand or by mechanical means from the coast or by compressed air ejectors from boats that gather the seaweeds settled in cavities at depths of about 25 metres ("wells"). To avoid fermentation, the seaweed should be gathered shortly after it has separated from its holdfast.

Gathering seaweeds by cutting or rooting them out from their beds. This work is done with rakes or grabs handled from boats or by scuba divers who operate from boats using compressed air bottles or, more frequently, a compressor on the boat connected to the diver by a hose ("hookah"). Gelidium usually occurs on rocky beds, Gracilaria on sandy ones. In general it is feasible to operate with divers in depths between 3 and 20 metres. In Japan, for many years, the seaweeds have been gathered by diving girls or "amas" who operte from floats and dive using only their lungs. These techniques of cutting or rooting out are used exclusively in some countries and are similar to the ones used for carrageenanophytes such as Chondrus crispus and other Chondrus species (Irish Moss) or alginophytes such as Macrocystis or Laminaria , adapting the equipment in each case to the morphological characteristics of each seaweed class.

Cultivation. Nowadays the need for greater quantities of agarophytes has brought about the introduction of cultivation of Gracilaria crops, along the lines used for carrageenophytes. However this cultivation has had only limited success and there are some aspects to be solved before it can be generally adopted. At the present time, cultivation for industrial purposes is undertaken in the People's Republic of China, its Taiwan Province and it is now being initiated in Chile (Ren, Wang and Chen, 1984 Ren and Chen, 1986 Cheuh and Chen, 1982 Yang, 1982 Pizarro and Barrales, 1986 Santelices and Ugarte, 1986).

The preservation of seaweeds, between the time of harvesting and their actual use by the agar manufacturer, is very important. To build a seaweed processing factory, which consumes seaweeds at the rate they are harvested, is not practical. Large scale agar manufacture makes it necessary to have available quantities of agarophytes stabilized in such a way that they can be carried long distances, at the least possible cost, and stored for a long time before processing.

The first step is preservation through dehydration, to avoid fermentation that first destroys the agar and then the seaweed. The second step is pressing the weed with a hydraulic press in bales of about 60 kg, to reduce the volume and return transportation and storage costs. Dehydration must be sufficient to guarantee the seaweed's preservation, otherwise an anaerobic fermentation will occur inside the bales causing high temperatures and even carbonization of the seaweeds during storage in warehouses. In general, the moisture content is best reduced to about 20% by natural or artificial drying. Obviously it is necessary to avoid wetting during transportation and/or storage.

In the case of Gracilaria the problem is more difficult to solve. The enzymatic hydrolysis of its agar occurs spontaneously even at relatively low moisture contents, but at variable rates depending on the Gracilaria species and its origin. Gracilaria harvested in India, Sri Lanka, Venezuela, Brazil, and generally in warm waters, has an agar (agarose) less resistant to enzymatic hydrolysis than the Chilean Gracilaria which is the most stable. Nevertheless, the stability of agar contained in Gracilaria is less than that of Gelidium Gelidium agar can be preserved in seaweeds indefinitely provided they have been well treated.

Hydrolysis of agar contained in Gracilaria can be due to endogenous enzymes or to the growth of Bacillus cereus . Pterocladia capillacea from the Azores behaves like Gelidium but the extent of hydrolysis of seaweeds such as Gelidiella , Ahnpheltia , and others has not been described.

The seaweeds imported by Japan in 1984 are shown in Figure 4a. Under the heading of "Gelidium", 678 tonnes were imported at a value of Yen 253 741 000 CIF (Yen 374 250 per tonne) the exchange rate at that time was US$ 1 = Yen 246.17 so an average CIF price was US$ 1 520 per tonne. Freight must be considered in this price, especially the high cost of the freight between countries far from Japan such as Chile (303 tonnes), Brazil (20 tonnes), Madagascar (74 tonnes) or South Africa (100 tonnes). These countries account for 73% of the seaweed imported as Gelidium . The seaweeds imported by Japan are high quality and exceptionally clean, otherwise it would not be possible to afford the freight costs. This applies to Gelidium , Gracilaria or any other agarophytes. These specifications, normally not so exact when the manufacturer is located near the harvesting place, greatly increase the harvesting and preparation costs.

The economic data for "Other Seaweeds" is more difficult to interpret because although these seaweeds are referred to as Gracilaria , they may include other agarophytes like Gelidiella , Pterocladia , Ahnpheltia , etc., with different agar contents and therefore different properties. Under the heading of "Other Seaweeds", 9 462 tonnes were imported (compared with Gelidium at 678 tonnes) with a value of Yen 2 882 525 000 (Yen 304 642 per tonne) or US$ 1 237 per tonne (CIF). The freight costs in this price must also be considered since more than 80% of the "Other Seaweeds" are imported from countries such as Chile (6 128 tonnes), Brazil (607 tonnes), Argentina (58 tonnes), and South Africa (895 tonnes).

Gracilaria is the major component of "Other Seaweeds". However two types of Gracilaria are imported and they are not distinguished from each other in the import statistics. One type is clean, dried seaweed. The other type is Gracilaria which has been subjected to a strong alkaline treatment in the exporting country this causes alkaline hydrolysis of sulphate groups, increasing the gel strength of the agar which is eventually extracted, although the yield is reduced. This treatment is expensive and for this reason the product obtained ("Colagar") brings a higher price than the untreated dried seaweed. All of this must be borne in mind when considering the average price of the "Other Seaweeds" which is calculted from the Japanese import statistics.


The existing literature on the evaluation of seaweeds as industrial sources of agar is confusing because in general the contributions have come from well intentioned scientists who often are unfamiliar with specification requirements, the different grades of commercial agar and the analytical methods used.

Firstly, the evaluations have been made from seaweeds which are perfectly dry and clean, like herbal samples, and therefore their data does not have any similarity to that obtained by the manufacturers who process hundreds or thousands of tonnes of commercial seaweeds arriving in very different stages of preservation, often mixed with significant quantities of impurities such as stones, shells, sand, other seaweeds, epiphytes, as well as other products added during gathering, drying, and packing (such as land weeds, leaves, wood, plastics, etc.). The quantities of salts that remain in the seaweeds after drying is another variable.

Secondly, the evaluation is frequently made without taking into account the characteristics of the agar obtained, or by comparing it only in some parameters (for instance with a bacteriological agar sample). After making some tests without knowing the real specifications for the products, and in many cases without knowledge of the usual analytical methods, it is declared to be similar. All of this is equivalent to determining the density of a rock and, seeing that it is 3.52, deducing that the rock is diamond.

Thirdly, an agarophyte evaluation is a much longer and complicated process than the one usually carried out and published in scientific articles. In our opinion it must be initiated with a series of tests or experiments on a laboratory scale. In principle we would make several extractions, combining some preliminary treatments with different extraction conditions. The previous experience of the person who is going to chose the experiments is very important if good results are to be obtained. Under these conditions it is usual to operate with glass equipment and with quantities of about 50 g of seaweed for each test. For normal work it is necessary to have between 400 and 500 g of dried seaweed.

Next, provided promising results have been obtained and a simplified quality control test has been performed, a pilot plant run should be the next step. An evaluation performed in a laboratory can be sufficient for a scientific publication but in industry, before working in a factory, we operate a pilot plant trial with quantities between 750 g and 1 kg of dried seaweeds in conditions as similar as possible to those of the industrial process. To carry out this trial it is convenient to have about 5 kg of dried seaweed available. Using the agar obtained in the pilot plant, complete analyses are made, as well as an evaluation of the product in practical applications. Knowledge of industrial manufacturing processes for agar is needed for this evaluation to be useful, as well as experience of actual specifications required by the different markets and by the practical applications of the product.

It is essential that agarophytes be correctly evaluated before starting operations in those countries that at present are studying their algal resources. For this, as soon as the quantities of agarophytes from a part of the coast have been estimated, even approximately, the quantity and quality of the agar in the seaweed should be evaluated in terms of its practical use. For this purpose it is important to have the cooperation of experienced agar manufacturers.

A very important point to be considered is the way representative samples are taken from large areas of agarophytes. Sampling is not as easy as it may seem. To have representative samples it is necessary to follow the classical sampling procedures and take some additional special precautions. The sample must be immediately packed in strong, waterproof, well fastened bags too often samples are received in broken packages containing extremely dried seaweeds and in many cases with significant quantities of sand outside the bag and spread, through the package.

As soon as the sample is received in the control laboratory, the impermeability of the plastic bag is verified and registered in the protocol. Next, on aliquots taken in such a way that their homogeneous composition is guaranteed, the following determinations must be made.

1. Moisture . Use a drying oven at 65°C.

2. Pure seaweed determination .

Seaweeds must be soaked in fresh water for at least two hours, with stirring, to eliminate soil and sand which are decanted, filtered, dried and weighed separately. Once the seaweeds are fully swelled the agarophytes must be manually separated from all the other materials such as rocks, shells, calcareous inclusions, other seaweeds, epiphytes, various vegetable remains, wood, plastic, etc. All these materials must be dried and weighed. Then the agarophytes are washed with water until clear (some samples, particularly Gracilaria , may contain clay). When cleaned they must be dried (in an oven at 65°C) and weighed the percentage of the sample which is "pure seaweed" is calculated.

3. Extraction - of an aliquot part of the sample

It is impossible to assign a general extraction method valid for any agarophyte. For many years we have been industrially evaluating a large number of agarophyte batches. They have come from the five continents and include Gelidium , Gelidiella , Pterocladia and Gracilaria species. We do know that it is impossible to give a valid extraction method for any agarophyte to evaluate its yield, obtaining at the same time a standard quality which allows evaluation to be useful from the point of view of the industry.

Nevertheless, we shall try to give here certain procedures that are only evaluation methods and should not be confused with industrial processes.

It is advisable to use 50 g or more in case the agarophytes have a lower percentage of "pure seaweed" than usual. Extraction conditions (pH, temperature, pressure, time, etc.) as well as the seaweed: water ratio must be adapted in each case so as to try to obtain an extract with approximately 1% agar.

A traditional Japanese method for Gelidium is the following. The seaweed (40 g) is washed three times. It is then placed in a beaker with water (40 ml, or more if necessary, to cover the seaweed which can be flattened). Adjust to pH4 using acetic acid. After 10 minutes the temperature is increased and maintained close to the boiling point for three minutes. Water is added to bring the total volume to 800 ml with this dilution the pH increases to approximately 6 unless it is adjusted with acetic acid or a dilute solution of caustic soda. The extraction is carried out at a temperature just below boiling point for 3-4 hours, checking the seaweed texture to determine the end of the extraction. The liquid is then filtered through a cloth and the residue is squeezed. As soon as the extract gels, it is subjected to freezing, or syneresis, and afterwards is dried and weighed.

In general Gelidium , Pterocladia or Gelidiella seaweeds can also be evaluated as follows. The seaweed is mixed with a solution of sodium carbonate (0.5%, 30 ml solution for each gram of seaweed) and held at approximately 90°C for 30 minutes, allowing the alkali to diffuse into the seaweed. The seaweed is washed with running water for 10 minutes. It is then extracted with water, 30 ml for each gram of seaweed, adjusting the pH with tartaric acid between 4.8-8.0 depending on the type of seaweed and on the extracting conditions. If extraction is done at boiling point (without pressure) it is usual to work between pH 4.8-6.0 and if it is done under pressure it will depend on the pressure used but at 127°C (1.5 -2 ) it is usual to operate between pH 6-8. The solution is filtered and the product is finished, either by freezing or syneresis, and dried.

In the case of certain Gracilaria species, it is necessary to make what is called a sulfate alkaline hydrolysis, working in stronger alkaline conditions to change the L-galactose 6-sulfate into 3,6-anhydro-L-galactose. For this purpose the diffusion is made with sodium hydroxide solution (at least 0.1M) for at least one hour at a temperature between 80-97°C, but with care not to extract the agar. The extraction which follows is carried out with stirring at practically neutral pH, without pressure (95-100°C), for a very variable time depending on the type of the Gracilaria used, but it can take several hours.

Then analytical control test will be needed to verify that the agar obtained meets the physico-chemical specifications that will be explained later.

Early studies of agar showed that it contained galactose, 3,6-anhydro-galactose (Hands and Peats, 1938 Percival, Somerville and Forbes, 1938) and inorganic sulfate bonded to the carbohydrate (Samec and Isajevic, 1922).

Structural studies have been based on the fractionation of agar by several methods, followed by chemical and enzymatic hydrolysis. The enzymatic hydrolysis studies of W. Yaphe have been of great importance. Subsequently the spectrochemical studies using infrared spectroscopy and nuclear magnetic resonance spectroscopy, particularly 13 C n.m.r., have explained many important points in the structure of these intricate polysaccharides.

Infrared spectroscopy is the most accessible method for many laboratories. Figure 8a shows different absorption bands that have been characterized for the agar spectrum. The typical bands of a carrageenan spectrum are also shown (Figure 8b) because many of its important uses are similar to those of agar and the spectra are useful for distinguishing the two. The bands at 1 540 and at 1 640 cm -1 are especially noteworthy. They come from the proteins existing in agar and about which only a few comments have been made before. The peak at 890 cm -1 has not been identified up to the present time.

N.M.R. is of great importance when studying these structures. However the technique is difficult and it requires 13 C n.m.r. equipment which only a few laboratories can afford. For this kind of work it is best to consult W. Yaphe's papers, published from 1977 - for example, Bhattacharjee, Hamer and Yaphe, (1979) Yaphe (1984) Lahaye, Rochas and Yaphe (1986).

Agar is now considered to consist of two fractions, agarose and agaropectin. These were first separated by Araki (1937) and the results were published in Japanese so they were not readily available to some research workers. For example Jones and Peats (1942) assigned a single structure to agar defining it as a long D-galactose chain residue, joined by 1,3-glycosidic links in the proposed structure, this chain was ended by a residue of L-galactose joined to the chain at C-4 and with C-6 semi-esterified by sulfuric acid. This false structure is still mentioned in some books on natural polymers and even in recently published encyclopedias.

Interest in agarose was lost until Hjerten, working under Tiselius at the University of Uppsala, began to look for an electrically neutral polysaccharide suitable for electrophoresis and chromatography. He published an improved method of separation based on the use of quaternary ammonium salts (Hjerten, 1962). A technique for agarose preparation using polyethylene glycol was reported by Russell, Mead and Polson (1964) and later this was patented with Polson (1965) named as the inventor. Both methods gave agarose of sufficient purity to allow the study of its structure.

Figure 5 shows the type, and approximate relative quantities, of the residues that can be separated from the total hydrolysis of agarose.

Figure 6 shows agarose to be a neutral, long-chain molecule formed by b -D-galactopyranose residues connected through C-1 and C-3 with 3,6-anhydro-L-galactose residues connected through C-2 and C-4. Both residues are repeated alternately. The links between the monomers have different resistance to chemical and enzymatic hydrolysis. 1,3- a links are more easily hydrolysed by enzymes ( Pseudomonas atlantica ) and neoagarobiose results. 1,4- b links are more easily hydrolysed by acid catalysts and yield agarobiose units. Nevertheless 1,4- b links make the polysaccharide chain particularly compact and resistant to breakage, as is found in the peptidoglycan of bacteria. The molecular weight assigned to non-degraded agarose is approximately 120 000. This weight has been determined by sedimentation measurements and it represents 400 agarbiose (or 800 hexose) units linked together.