![Agarplate redbloodcells edit](https://upload.wikimedia.org/wikipedia/commons/5/56/Agarplate_redbloodcells_edit.jpg)
Agar ( or ), or agar-agar, is a
jelly-like substance consisting of
polysaccharides
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
obtained from the cell walls of some species of red algae, primarily from
ogonori
''Gracilaria'' is a genus of red algae (Rhodophyta) notable for its economic importance as an agarophyte, as well as its use as a food for humans and various species of shellfish. Various species within the genus are cultivated among Asia, South ...
(''
Gracilaria
''Gracilaria'' is a genus of red algae (Rhodophyta) notable for its economic importance as an agarophyte, as well as its use as a food for humans and various species of shellfish. Various species within the genus are cultivated among Asia, South ...
'') and "tengusa" (''
Gelidiaceae
The Gelidiaceae is a small family of red algae containing eight genera. Many species of this algae are used to make agar.
Uses
Agar can be derived from many types of red seaweeds, including those from families such as ''Gelidiaceaae'', ''Gracila ...
''). As found in nature, agar is a mixture of two components, the linear
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
agarose
Agarose is a heteropolysaccharide, generally extracted from certain red seaweed. It is a linear polymer made up of the repeating unit of agarobiose, which is a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose. Agarose is ...
and a heterogeneous mixture of smaller molecules called
agaropectin
Agaropectin is one of the two main components of agar and mainly consists of D-glucuronic acid and pyruvic acid.
Structure
Agaropectin is a sulphated galactan mixture which composes agar by 30% composition. It is the component of agar that is no ...
.
It forms the supporting structure in the cell walls of certain species of algae and is released on boiling. These algae are known as
agarophyte
An agarophyte is a seaweed, typically a red alga, that produces the hydrocolloid agar in its cell wall
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes ...
s, belonging to the
Rhodophyta
Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majorit ...
(red algae) phylum.
The processing of food-grade agar removes the agaropectin, and the commercial product is essentially pure agarose.
Agar has been used as an ingredient in
dessert
Dessert is a course that concludes a meal. The course consists of sweet foods, such as confections, and possibly a beverage such as dessert wine and liqueur. In some parts of the world, such as much of Greece and West Africa, and most parts o ...
s throughout Asia and also as a solid
substrate to contain
culture media
A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Different ...
for
microbiological
Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, pro ...
work. Agar can be used as a
laxative
Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation.
Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubri ...
; an
appetite suppressant
An anorectic or anorexic is a drug which reduces appetite, resulting in lower food consumption, leading to weight loss. By contrast, an appetite stimulant is referred to as orexigenic.
The term is (from the Greek ''ἀν-'' (an-) = "without" ...
; a
vegan
Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. ...
substitute for
gelatin
Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
; a thickener for
soup
Soup is a primarily liquid food, generally served warm or hot (but may be cool or cold), that is made by combining ingredients of meat or vegetables with stock, milk, or water. Hot soups are additionally characterized by boiling soli ...
s; in
fruit preserves
Fruit preserves are preparations of fruits whose main preserving agent is sugar and sometimes acid, often stored in glass jars and used as a condiment or spread.
There are many varieties of fruit preserves globally, distinguished by the met ...
, ice cream, and other desserts; as a clarifying agent in
brewing
Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer ...
; and for
sizing
Sizing or size is a substance that is applied to, or incorporated into, other materials—especially papers and textiles—to act as a protective filler or glaze. Sizing is used in papermaking and textile manufacturing to change the absorptio ...
paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distribu ...
and fabrics.
Etymology
The word "agar" comes from agar-agar, the
Malay name for red algae (''
Gigartina'', ''
Gracilaria
''Gracilaria'' is a genus of red algae (Rhodophyta) notable for its economic importance as an agarophyte, as well as its use as a food for humans and various species of shellfish. Various species within the genus are cultivated among Asia, South ...
'') from which the jelly is produced. It is also known as Kanten ( ja, 寒天) (from the phrase ''kan-zarashi
tokoroten'' () or “cold-exposed agar”), Japanese isinglass, China grass, Ceylon moss or Jaffna moss. ''Gracilaria lichenoides'' is specifically referred to as agal-agal or Ceylon agar.
History
![Ogo](https://upload.wikimedia.org/wikipedia/commons/9/92/Ogo.jpg)
Agar may have been discovered in Japan in 1658 by Mino Tarōzaemon (), an innkeeper in current
Fushimi-ku, Kyoto
is one of the eleven wards in the city of Kyoto, in Kyoto Prefecture, Japan. Famous places in Fushimi include the Fushimi Inari Shrine, with thousands of torii lining the paths up and down a mountain; Fushimi Castle, originally built by Toyoto ...
who, according to legend, was said to have discarded surplus seaweed soup (
Tokoroten
is a dish in Japanese cuisine made from agarophytes. Tokoroten has been eaten by the Japanese for over a thousand years. Tokoroten is thought to have been introduced to Japan from China during the Nara period. Tokoroten was traditionally made by ...
) and noticed that it gelled later after a winter night's freezing.
Over the following centuries, agar became a common gelling agent in several Southeast Asian cuisines.
Agar was first subjected to chemical analysis in 1859 by the French chemist
Anselme Payen
Anselme Payen (; 6 January 1795 – 12 May 1871) was a French chemist known for discovering the enzyme diastase, and the carbohydrate cellulose.
Biography
Payen was born in Paris. He began studying science with his father when he was a 13-ye ...
, who had obtained agar from the marine algae ''Gelidium corneum''.
Beginning in the late 19th century, agar began to be used as a solid medium for growing various microbes. Agar was first described for use in microbiology in 1882 by the German microbiologist
Walther Hesse
Walther Hesse (27 December 1846 – 19 July 1911) is best known for his work in microbiology, specifically his work with his wife Fanny Hesse in developing agar as a medium for culturing microorganisms.
Biography
He was born in Bischofswerda, ...
, an assistant working in
Robert Koch's laboratory, on the suggestion of his wife
Fanny Hesse
Fanny Hesse (born Angelina Fanny Eilshemius, June 22, 1850 – December 1, 1934) is best known for her work in microbiology alongside her husband, Walther Hesse. Following her initial suggestion of using agar as an alternative to gelatin, they w ...
.
Agar quickly supplanted gelatin as the base of microbiological media, due to its higher melting temperature, allowing microbes to be grown at higher temperatures without the media liquefying.
With its newfound use in microbiology, agar production quickly increased. This production centered on Japan, which produced most of the world's agar until World War II.
However, with the outbreak of World War II, many nations were forced to establish domestic agar industries in order to continue microbiological research.
[ Around the time of World War II, approximately 2,500 tons of agar were produced annually.][ By the mid-1970s, production worldwide had increased dramatically to approximately 10,000 tons each year.][ Since then, production of agar has fluctuated due to unstable and sometimes over-utilized seaweed populations.]
Composition
Agar consists of a mixture of two polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...
s: agarose and agaropectin, with agarose making up about 70% of the mixture.[ ]Agarose
Agarose is a heteropolysaccharide, generally extracted from certain red seaweed. It is a linear polymer made up of the repeating unit of agarobiose, which is a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose. Agarose is ...
is a linear polymer, made up of repeating units of agarobiose, a disaccharide made up of D-galactose and 3,6-anhydro-L-galactopyranose.[ Agaropectin is a heterogeneous mixture of smaller molecules that occur in lesser amounts, and is made up of alternating units of D-galactose and L-galactose heavily modified with acidic side-groups, such as sulfate and pyruvate.]
Agar exhibits hysteresis
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
, solidifying at about 32–40 °C (305–313 K, 90–104 °F) but melting at 85 °C (358 K, 185 °F). This property lends a suitable balance between easy melting and good gel stability at relatively high temperatures. Since many scientific applications require incubation at temperatures close to human body temperature (37 °C), agar is more appropriate than other solidifying agents that melt at this temperature, such as gelatin.
Uses
Culinary
Agar-agar is a natural vegetable gelatin
Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
counterpart. It is white and semi-translucent
In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions ...
when sold in packages as washed and dried strips or in powdered form. It can be used to make jellies, puddings
Pudding is a type of food. It can be either a dessert or a savoury (salty or spicy) dish served as part of the main meal.
In the United States, ''pudding'' means a sweet, milk-based dessert similar in consistency to egg-based custards, inst ...
, and custard
Custard is a variety of culinary preparations based on sweetened milk, cheese, or cream cooked with egg or egg yolk to thicken it, and sometimes also flour, corn starch, or gelatin. Depending on the recipe, custard may vary in consistency fr ...
s. When making jelly, it is boiled in water until the solids dissolve. Sweetener, flavoring, coloring, fruits and or vegetables are then added, and the liquid is poured into molds to be served as desserts and vegetable aspic
Aspic or meat jelly () is a savory gelatin made with a meat stock or broth, set in a mold to encase other ingredients. These often include pieces of meat, seafood, vegetable, or eggs. Aspic is also sometimes referred to as ''aspic gelée'' or ' ...
s or incorporated with other desserts such as a layer of jelly in a cake
Cake is a flour confection made from flour, sugar, and other ingredients, and is usually baked. In their oldest forms, cakes were modifications of bread, but cakes now cover a wide range of preparations that can be simple or elaborate ...
.
Agar-agar is approximately 80% dietary fiber
Dietary fiber (in British English fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition, and can be grouped generally by t ...
, so it can serve as an intestinal regulator. Its bulking quality has been behind fad diet
A fad diet is a diet that becomes popular for a short time, similar to fads in fashion, without being a standard dietary recommendation, and often making unreasonable claims for fast weight loss or health improvements. There is no single defi ...
s in Asia, for example the ''kanten'' (the Japanese word for agar-agar) diet. Once ingested, ''kanten'' triples in size and absorbs water. This results in the consumers feeling fuller.
Asian culinary
One use of agar in Japanese cuisine
Japanese cuisine encompasses the regional and traditional foods of Japan, which have developed through centuries of political, economic, and social changes. The traditional cuisine of Japan ( Japanese: ) is based on rice with miso soup and oth ...
(Wagashi
are traditional Japanese confections that are often served with green tea, especially the types made of ''mochi'', ''anko'' ( azuki bean paste), and fruit. ''Wagashi'' are typically made from plant-based ingredients.
History
In Japan, the wo ...
) is ''anmitsu
Anmitsu (, rarely ) is a Japanese dessert that dates to the Meiji era.
It is made of small cubes of agar jelly, a white translucent jelly made from red algae. The agar is dissolved with water (or fruit juice such as apple juice) to make the je ...
'', a dessert made of small cubes of agar jelly and served in a bowl with various fruits or other ingredients. It is also the main ingredient in ''mizu yōkan'', another popular Japanese food. In Philippine cuisine
Filipino cuisine ( fil, lutong Pilipino/pagkaing Pilipino) is composed of the cuisines of more than a hundred distinct ethnolinguistic groups found throughout the Philippine archipelago. A majority of mainstream Filipino dishes that compose Fi ...
, it is used to make the jelly bars in the various gulaman
''Gulaman'', in Filipino cuisine, is a bar, or powdered form, of dried agar or carrageenan used to make jelly-like desserts. In common usage, it also usually refers to the refreshment ''sago't gulaman'', sometimes referred to as ''samalamig'' ...
refreshments like ''Sago't Gulaman'', ''Samalamig'', or desserts such as ''buko pandan'', ''agar flan'', ''halo-halo
Halo-halo, correctly spelled ''haluhalo'', Tagalog for "mixed" (the more common spelling instead literally equating to "mix-mix") is a popular cold dessert in the Philippines made up of crushed ice, evaporated milk or coconut milk, and vari ...
'', ''fruit cocktail jelly'', and the black and red ''gulaman'' used in various fruit salads. In Vietnamese cuisine
Vietnamese cuisine encompasses the foods and beverages of Vietnam. Meals feature a combination of five fundamental tastes ( vi, ngũ vị, links=no, label=none): sweet, salty, bitter, sour, and spicy. The distinctive nature of each dish refle ...
, jellies made of flavored layers of agar agar, called ''thạch'', are a popular dessert, and are often made in ornate molds for special occasions. In Indian cuisine
Indian cuisine consists of a variety of regional and traditional cuisines native to India. Given the diversity in soil, climate, culture, ethnic groups, and occupations, these cuisines vary substantially and use locally available spices, he ...
, agar is used for making desserts. In Burmese cuisine
Burmese cuisine () encompasses the diverse regional culinary traditions of Myanmar, which have developed through longstanding agricultural practices, centuries of sociopolitical and economic change, and cross-cultural contact and trade with ne ...
, a sweet jelly known as ''kyauk kyaw'' is made from agar. Agar jelly is widely used in Taiwanese
Taiwanese may refer to:
* Taiwanese language, another name for Taiwanese Hokkien
* Something from or related to Taiwan ( Formosa)
* Taiwanese aborigines, the indigenous people of Taiwan
* Han Taiwanese, the Han people of Taiwan
* Taiwanese people, ...
bubble tea
Bubble tea (also known as pearl milk tea, bubble milk tea, tapioca milk tea, boba tea, or boba; , ) is a tea-based drink that originated in Taiwan in the early 1980s. Taiwanese immigrants brought it to the United States in the 1990s, initially ...
.
Other culinary
It can be used as addition to or as a replacement for pectin
Pectin ( grc, πηκτικός ': "congealed" and "curdled") is a heteropolysaccharide, a structural acid contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal, chemical component of ...
in jams and marmalades, as a substitute to gelatin for its superior gelling properties, and as a strengthening ingredient in souffles and custards. Another use of agar-agar is in a Russian
Russian(s) refers to anything related to Russia, including:
*Russians (, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries
*Rossiyane (), Russian language term for all citizens and peo ...
dish ''ptich'ye moloko'' ( bird's milk), a rich jellified custard (or soft meringue
Meringue (, ; ) is a type of dessert or candy, often associated with Swiss, French, Polish and Italian cuisines, traditionally made from whipped egg whites and sugar, and occasionally an acidic ingredient such as lemon, vinegar, or cream of ...
) used as a cake filling or chocolate-glazed as individual sweets.
Agar-agar may also be used as the gelling agent in gel clarification, a culinary technique used to clarify stocks, sauces, and other liquids. Mexico
Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
has traditional candies made out of Agar gelatin, most of them in colorful, half-circle shapes that resemble a melon
A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a "pepo". The ...
or watermelon
Watermelon (''Citrullus lanatus'') is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 varieti ...
fruit slice, and commonly covered with sugar. They are known in Spanish as ''Dulce de Agar'' (Agar sweets)
Agar-agar is an allowed nonorganic/nonsynthetic additive used as a thickener, gelling agent, texturizer, moisturizer, emulsifier, flavor enhancer, and absorbent in certified organic foods.
Microbiology
Agar plate
An agar plate or Petri dish
A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...
is used to provide a growth medium
A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation or small plants like the moss ''Physcomitrella patens''. Differen ...
using a mix of agar and other nutrients in which microorganisms, including bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, can be cultured and observed under the microscope. Agar is indigestible for many organisms so that microbial growth does not affect the gel used and it remains stable. Agar is typically sold commercially as a powder that can be mixed with water and prepared similarly to gelatin before use as a growth medium. Other ingredients are added to the agar to meet the nutritional needs of the microbe
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s. Many microbe-specific formulations are available because some microbes prefer certain environmental conditions over others. Agar is often dispensed using a sterile media dispenser
A media dispenser or a culture media dispenser is a device for repeatedly delivering small fixed volumes (typically between 1 ml and 50 ml) of liquid such as a laboratory growth medium like molten agar or caustic or volatile solvents li ...
.
Types of agar in microbiology
Different algae produce various types of agar. Each agar has unique properties that suit different purposes. Because of the agarose component, the agar solidifies. When heated, agarose has the potential to melt and then solidify. Because of this property, they are referred to as "physical gels." Polyacrylamide polymerization is an irreversible process, and the resulting products are known as chemical gels.
Given below is a list of different types of agar that support the different strains of bacterial growth:
# Blood Agar : A bacterial growth media is blood agar. It is mostly used to cultivate pathogenic bacteria such as Streptococci. Ordinary growth media does not support the development of such organisms. They can only grow in blood agar because it contains inhibitors for several bacterial families
# Luria Bertani (LB) Agar : are nutrient-rich plates used for bacterial growth. They are frequently utilized in cloning operations to increase the number of antibiotic-resistant, competent microorganisms. The same ingredients, without the agar, can be used to make liquid LB medium.
# Chocolate Agar : Chocolate Agar (CAP or CHOC) is a nonselective improved medium used to detect and isolate finicky pathogens.Chocolate agar is created by heating blood agar, which subsequently splits the red blood cell (RBC), releasing nutrients that help in the development of fastidious bacteria such as Haemophilus and Neisseria species.The term comes from the fact that the absence of RBC results in the hue chocolate brown.Chocolate agar is very identical to blood agar, except that the red blood cells are destroyed during the manufacturing process when they are introduced to the molten agar foundation. This causes cell lysis, which releases intracellular nutrition such as hemoglobin, Hemin ("X" factors), and the coenzyme nicotinamide-adenine dinucleotide (NAD and "V" factor) into the agar, which is then utilized by fastidious bacteria.Chocolate agar is very identical to blood agar, except that the red blood cells are destroyed during the manufacturing process when they are introduced to the molten agar foundation. This causes cell lysis, which releases intracellular nutrition such as hemoglobin, Hemin ("X" factors), and the coenzyme nicotinamide-adenine dinucleotide (NAD and "V" factor) into the agar, which is then utilized by fastidious bacteria
# MacConkey Agar : Alfred Theodore MacConkey produced the first solid differential medium, (MAC), in the twentieth century. MacConkey agar is a selective and differential media used for the isolation and differentiation of non-fastidious gram-negative rods, notably members of the Enterobacteriaceae and Pseudomonas genera. MacConkey Agar Applications: Gram-negative intestinal bacteria are isolated using MacConkey agar. It is used to distinguish lactose fermenting gram-negative bacteria from lactose non-fermenting gram-negative bacteria. It's used to isolate coliforms and intestinal pathogens from water, dairy products, and biological samples
# Nutrient Agar : Nutrient Agar is a basic culture medium that is often used for the cultivation of non-fastidious microorganisms, as well as for quality control and purity checking prior to biochemical or serological testing. By supplementing the medium with serum or blood, nutrient media may also be utilized to cultivate picky microorganisms .Nutrient Agar is an excellent medium for demonstration and teaching because it allows cultures to survive at room temperature for longer periods of time without the risk of overgrowth that occurs with more nutritional mediums .This medium has a very basic formula that has been preserved and is still commonly employed in the microbiological evaluation of a wide range of materials, as well as being recommended by standard procedures .Nutrient agar is a general-purpose medium that is primarily used for regular culture or to assure microorganism survival .It is one of the most essential and widely used non-selective medium for regular microorganism culture. Many bacteria that are not particularly fastidious have been grown and counted on nutrient agar .By adding different biological fluids such as horse or sheep blood, serum, egg yolk, and so on, the media can be made suitable for the cultivation of other fastidious organisms.
# Neomycin Agar : Neomycin blood agar is a popular selective medium for isolating vancomycin-resistant enterococci from feces; however, not all isolates are recovered using this medium, perhaps due to excessive neomycin concentrations.
Motility assays
As a gel, an agar or agarose medium is porous and therefore can be used to measure microorganism motility and mobility. The gel's porosity is directly related to the concentration of agarose in the medium, so various levels of effective viscosity (from the cell's "point of view") can be selected, depending on the experimental objectives.
A common identification assay involves culturing a sample of the organism deep within a block of nutrient agar. Cells will attempt to grow within the gel structure. Motile species will be able to migrate, albeit slowly, throughout the gel, and infiltration rates can then be visualized, whereas non-motile species will show growth only along the now-empty path introduced by the invasive initial sample deposition.
Another setup commonly used for measuring chemotaxis and chemokinesis utilizes the under-agarose cell migration assay, whereby a layer of agarose gel is placed between a cell population and a chemoattractant. As a concentration gradient develops from the diffusion of the chemoattractant into the gel, various cell populations requiring different stimulation levels to migrate can then be visualized over time using microphotography as they tunnel upward through the gel against gravity along the gradient.
Plant biology
Research grade agar is used extensively in plant biology as it is optionally supplemented with a nutrient and/or vitamin mixture that allows for seedling germination in Petri dishes under sterile conditions (given that the seeds are sterilized as well). Nutrient and/or vitamin supplementation for ''Arabidopsis thaliana
''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land.
A winter a ...
'' is standard across most experimental conditions. Murashige & Skoog (MS) nutrient mix and Gamborg's B5 vitamin mix in general are used. A 1.0% agar/0.44% MS+vitamin dH2O solution is suitable for growth media between normal growth temps.
When using agar, within any growth medium, it is important to know that the solidification of the agar is pH-dependent. The optimal range for solidification is between 5.4 and 5.7. Usually, the application of potassium hydroxide is needed to increase the pH to this range. A general guideline is about 600 µl 0.1M KOH per 250 ml GM. This entire mixture can be sterilized using the liquid cycle of an autoclave
An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform sterilizat ...
.
This medium nicely lends itself to the application of specific concentrations of phytohormones etc. to induce specific growth patterns in that one can easily prepare a solution containing the desired amount of hormone, add it to the known volume of GM, and autoclave to both sterilize and evaporate off any solvent that may have been used to dissolve the often-polar hormones. This hormone/GM solution can be spread across the surface of Petri dishes sown with germinated and/or etiolated seedlings.
Experiments with the moss
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
''Physcomitrella patens
''Physcomitrium patens'', (synonym: ''Physcomitrella patens'' ) the spreading earthmoss, is a moss (bryophyte) used as a model organism for studies on plant evolution, development, and physiology.
Distribution and ecology
''Physcomitrella pat ...
'', however, have shown that choice of the gelling agent – agar or Gelrite – does influence phytohormone
Plant hormone (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from embryogenesis, the regulation of organ size, pat ...
sensitivity of the plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
cell culture
Cell culture or tissue culture is the process by which cells are grown under controlled conditions, generally outside of their natural environment. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This te ...
.[
]
Other uses
Agar is used:
* As an impression material in dentistry
Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the teeth, gums, and mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, disorders, and conditions o ...
.
* As a medium to precisely orient the tissue specimen and secure it by agar pre-embedding (especially useful for small endoscopy biopsy specimens) for histopathology
Histopathology (compound of three Greek words: ''histos'' "tissue", πάθος ''pathos'' "suffering", and -λογία '' -logia'' "study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Spe ...
processing
* To make salt bridge
In electrochemistry, a salt bridge or ion bridge is a laboratory device used to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell), a type of electrochemical cell. It maintains electrical neutrality within the in ...
s and gel plugs for use in electrochemistry
Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...
.
* In formicarium
A formicarium or ant farm is a vivarium which is designed primarily for the study of ant colonies and how ants behave. Those who study ant behavior are known as myrmecologists.
History
The formicarium was invented by Charles Janet, a French ...
s as a transparent substitute for sand and a source of nutrition.
* As a natural ingredient in forming modeling clay
Modelling clay or modelling compound is any of a group of malleable substances used in building and sculpting. The material compositions and production processes vary considerably.
Ceramic clay
Ceramic clays are water-based substances made f ...
for young children to play with.
* As an allowed biofertilizer component in organic farming.
* As a substrate for precipitin reactions in immunology
Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see there ...
.
* At different times as a substitute for gelatin
Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
in photographic emulsion
Photographic emulsion is a light-sensitive colloid used in film-based photography. Most commonly, in silver-gelatin photography, it consists of silver halide crystals dispersed in gelatin. The emulsion is usually coated onto a substrate of g ...
s, arrowroot
Arrowroot is a starch obtained from the rhizomes (rootstock) of several tropical plants, traditionally ''Maranta arundinacea'', but also Florida arrowroot from ''Zamia integrifolia'', and tapioca from cassava (''Manihot esculenta''), which is oft ...
in preparing silver paper and as a substitute for fish glue
Animal glue is an adhesive that is created by prolonged boiling of animal connective tissue in a process called rendering. In addition to being used as an adhesive it is used for coating and sizing, in decorative composition ornaments, and as a ...
in resist etching.
* As an MRI elastic gel phantom to mimic tissue mechanical properties in Magnetic Resonance Elastography
Gelidium agar is used primarily for bacteriological plates. Gracilaria agar is used mainly in food applications.
In 2016, AMAM, a Japanese company, developed a prototype for Agar-based commercial packaging
Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a co ...
system called Agar Plasticity, intended as a replacement for oil-based plastic packaging.
See also
* Agarose gel electrophoresis
Agarose gel electrophoresis is a method of gel electrophoresis used in biochemistry, molecular biology, genetics, and clinical chemistry to separate a mixed population of macromolecules such as DNA or proteins in a matrix of agarose, one of the ...
* Algaculture
Algaculture is a form of aquaculture involving the farming of species of algae.
The majority of algae that are intentionally cultivated fall into the category of microalgae (also referred to as phytoplankton, microphytes, or planktonic algae). M ...
* Alginic acid
Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, its salts are known as alginates. Its colou ...
* Asepsis
Asepsis is the state of being free from disease-causing micro-organisms (such as pathogenic bacteria, viruses, pathogenic fungi, and parasites). There are two categories of asepsis: medical and surgical. The modern day notion of asepsis is deriv ...
* Carrageenan
Carrageenans or carrageenins ( ; ) are a family of natural linear sulfated polysaccharides that are extracted from red edible seaweeds. Carrageenans are widely used in the food industry, for their gelling, thickening, and stabilizing properties. T ...
* Gellan gum
Gellan gum is a water-soluble anionic polysaccharide produced by the bacterium '' Sphingomonas elodea'' (formerly ''Pseudomonas elodea'' based on the taxonomic classification at the time of its discovery). The gellan-producing bacterium was disco ...
* Immunodiffusion
Immunodiffusion is a diagnostic test which involves diffusion through a substance such as agar which is generally soft gel agar (2%) or agarose (2%), used for the detection of antibodies or antigen.
The commonly known types are:
:# Single diffusi ...
* Immunoelectrophoresis
Immunoelectrophoresis is a general name for a number of biochemical methods for separation and characterization of proteins based on electrophoresis and reaction with antibodies. All variants of immunoelectrophoresis require immunoglobulins, a ...
* Lima bean agar
* Ouchterlony double immunodiffusion
* R2a agar
* Radial immunodiffusion
Radial immunodiffusion (RID) or Mancini method, Mancini immunodiffusion or single radial immunodiffusion assay, is an immunodiffusion technique used in immunology to determine the quantity or concentration of an antigen in a sample.
Description ...
* SEAgel
SEAgel (Safe Emulsion Agar gel) is one of a class of high-tech foam materials known as aerogels. It is an excellent thermal insulator and among the least dense solids known. SEAgel was invented by Robert Morrison at the Lawrence Livermore Nation ...
* Tokoroten
is a dish in Japanese cuisine made from agarophytes. Tokoroten has been eaten by the Japanese for over a thousand years. Tokoroten is thought to have been introduced to Japan from China during the Nara period. Tokoroten was traditionally made by ...
References
External links
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{{Authority control
Edible thickening agents
Microbiological gelling agent
Dental materials
Algal food ingredients
Red algae
Gels
Polysaccharides
Japanese inventions
Food stabilizers
Jams and jellies
E-number additives
Impression material