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47-424: For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid-liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point. It melts at 85 °C (185 °F) and solidifies from 32 to 40 °C (90 to 104 °F). Most liquids freeze by crystallization, formation of crystalline solid from

94-528: A gel below about 32–42 °C (305–315 K; 90–108 °F), which is called the gel point , and melts above 85 °C (358 K; 185 °F), which is the melting point . Hysteresis is the property of having a difference between the gel point and melting point temperatures. 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

141-485: A laxative ; an appetite suppressant ; a vegan substitute for gelatin ; a thickener for soups ; in fruit preserves , ice cream, and other desserts; as a clarifying agent in brewing ; and for sizing paper and fabrics. The word agar comes from agar-agar , the Malay name for red algae ( Gigartina , Eucheuma , Gracilaria ) from which the jelly is produced. It is also known as Kanten ( Japanese : 寒天 ) (from

188-434: 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 , glucuronate , and pyruvate . Agar exhibits a phenomenon known as hysteresis whereby, when mixed with water, it solidifies and forms

235-529: A food additive in Japan is alleged to have been discovered in 1658 by Mino Tarōzaemon ( 美濃 太郎 左 衞 門 ), an innkeeper in current Fushimi-ku, Kyoto who, according to legend, was said to have discarded surplus seaweed soup ( Tokoroten ) and noticed that it gelled later after a winter night's freezing. Agar was first subjected to chemical analysis in 1859 by the French chemist Anselme Payen , who had obtained agar from

282-405: A freezing point, as there is no abrupt phase change at any specific temperature. Instead, there is a gradual change in their viscoelastic properties over a range of temperatures. Such materials are characterized by a glass transition that occurs at a glass transition temperature , which may be roughly defined as the "knee" point of the material's density vs. temperature graph. Because vitrification

329-399: 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

376-587: A gel-like texture is also used similarly among the Visayan peoples and have been recorded in the even earlier Diccionario De La Lengua Bisaya, Hiligueina y Haraia de la isla de Panay y Sugbu y para las demas islas (c.1637) of the Augustinian missionary Alonso de Méntrida (in Spanish) . In the book, Méntrida describes gusô as being cooked until it melts, and then allowed to congeal into a sour dish. In Ambon Island in

423-474: A hypothetical nucleus is too small, the energy that would be released by forming its volume is not enough to create its surface, and nucleation does not proceed. Freezing does not start until the temperature is low enough to provide enough energy to form stable nuclei. In presence of irregularities on the surface of the containing vessel, solid or gaseous impurities, pre-formed solid crystals, or other nucleators, heterogeneous nucleation may occur, where some energy

470-509: A process called hardening , which allows them to survive temperatures below 0 °C for weeks to months. The nematode Haemonchus contortus can survive 44 weeks frozen at liquid nitrogen temperatures. Other nematodes that survive at temperatures below 0 °C include Trichostrongylus colubriformis and Panagrolaimus davidi . Many species of reptiles and amphibians survive freezing. Human gametes and 2-, 4- and 8-cell embryos can survive freezing and are viable for up to 10 years,

517-623: A process known as cryopreservation . Experimental attempts to freeze human beings for later revival are known as cryonics . Freezing is a common method of food preservation that slows both food decay and the growth of micro-organisms . Besides the effect of lower temperatures on reaction rates , freezing makes water less available for bacteria growth. Freezing is a widely used method of food preservation. Freezing generally preserves flavours, smell and nutritional content. Freezing became commercially viable , Agar Agar ( / ˈ eɪ ɡ ɑːr / or / ˈ ɑː ɡ ər / ), or agar-agar ,

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564-401: A replacement for) pectin 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 dish ptich'ye moloko ( bird's milk ), a rich jellified custard (or soft meringue ) used as a cake filling or chocolate-glazed as individual sweets. Agar-agar may also be used as

611-424: A thickener, gelling agent, texturizer, moisturizer, emulsifier, flavor enhancer, and absorbent in certified organic foods. An agar plate or Petri dish is used to provide a growth medium using a mix of agar and other nutrients in which microorganisms, including bacteria and fungi , can be cultured and observed under the microscope. Agar is indigestible for many organisms so that microbial growth does not affect

658-399: Is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae , primarily from "ogonori" ( Gracilaria ) and "tengusa" ( Gelidiaceae ). As found in nature, agar is a mixture of two components, the linear polysaccharide agarose and a heterogeneous mixture of smaller molecules called agaropectin . It forms the supporting structure in

705-675: Is a latent heat , and is known as the enthalpy of fusion and is exactly the same as the energy required to melt the same amount of the solid. Low-temperature helium is the only known exception to the general rule. Helium-3 has a negative enthalpy of fusion at temperatures below 0.3 K. Helium-4 also has a very slightly negative enthalpy of fusion below 0.8 K. This means that, at appropriate constant pressures, heat must be added to these substances in order to freeze them. Certain materials, such as glass and glycerol , may harden without crystallizing; these are called amorphous solids . Amorphous materials, as well as some polymers, do not have

752-825: Is a macronutrient that provides a nitrogen source for all bacterial cell types. Other fastidious organisms may require the addition of different biological fluids such as horse or sheep blood, serum, egg yolk, and so on. Agar plates can also be selective, and can be used to promote the growth of bacteria of interest while inhibiting others. A variety of chemicals may be added to create an environment favourable for specific types of bacteria or bacteria with certain properties, but not conducive for growth of others. For example, antibiotics may be added in cloning experiments whereby bacteria with antibiotic-resistant plasmid are selected. In addition to antibiotic treated agar, other selective and indicator agar plates include TCBS agar and MacConkey agar. Thiosulfate citrate bile salts sucrose (TCBS) agar

799-421: Is a non-equilibrium process, it does not qualify as freezing, which requires an equilibrium between the crystalline and liquid state. The size of substances increases or expands on being heated. This increase in the size of a body due to heating is called thermal expansion .. Thermal expansion takes place in all objects and in all states of matter. However, different substances have different rates of expansion for

846-427: Is almost always an exothermic process, meaning that as liquid changes into solid, heat and pressure are released. This is often seen as counter-intuitive, since the temperature of the material does not rise during freezing, except if the liquid were supercooled . But this can be understood since heat must be continually removed from the freezing liquid or the freezing process will stop. The energy released upon freezing

893-567: Is an irreversible process, and the resulting products are known as chemical gels. There are a variety of different types of agar that support the growth of different microorganisms. A nutrient agar may be permissive, allowing for the cultivation of any non-fastidious microorganisms; a commonly-used nutrient agar for bacteria is the Luria Bertani (LB) agar which contains lysogeny broth , a nutrient-rich medium used for bacterial growth. Additionally, 2216 Marine Broth (MB) agar, with high salt content,

940-565: Is from the Vocabulario de la lengua tagala (1754) by the Jesuit priests Juan de Noceda and Pedro de Sanlucar, where golaman or gulaman was defined as "una yerva, de que se haze conserva a modo de Halea, naze en la mar" ("a herb, from which a jam-like preserve is made, grows in the sea"), with an additional entry for guinolaman to refer to food made with the jelly. Carrageenan , derived from gusô ( Eucheuma spp.), which also congeals into

987-412: Is known. Agar is often dispensed using a sterile media dispenser . 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". In contrast, polyacrylamide polymerization

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1034-472: Is more appropriate than other solidifying agents that melt at this temperature, such as gelatin. Agar-agar is a natural vegetable gelatin counterpart. It is white and semi- translucent when sold in packages as washed and dried strips or in powdered form. It can be used to make jellies, puddings , and custards . When making jelly, it is boiled in water until the solids dissolve. Sweetener, flavoring, coloring, fruits and or vegetables are then added, and

1081-487: Is optimized for growing heterotrophic marine bacteria like those of the Vibrio genus, while Terrific Broth (TB) agar is used to non-selectively culture high yields of the bacterium E. coli . More generally, enriched media is an agar variety that is infused with the necessary nutrients required by fastidious organisms to grow. Despite the large diversity of agar mediums, yeast extract is a common ingredient across all varieties as it

1128-609: Is released by the partial destruction of the previous interface, raising the supercooling point to be near or equal to the melting point. The melting point of water at 1 atmosphere of pressure is very close to 0 °C (32 °F; 273 K), and in the presence of nucleating substances the freezing point of water is close to the melting point, but in the absence of nucleators water can supercool to −40 °C (−40 °F; 233 K) before freezing. Under high pressure (2,000 atmospheres ) water will supercool to as low as −70 °C (−94 °F; 203 K) before freezing. Freezing

1175-437: 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

1222-480: Is used to differentiate Vibrio species based on their sucrose metabolism, since only some will metabolize the sucrose in the plate and change its pH. Indicator dyes included in the gel will display a visual change of the pH by changing the gel color from green to yellow. MacConkey agar contains bile salts and crystal violet to selectively grow gram-negative bacteria and differentiate between species using pH-indicator dyes that demonstrate lactose metabolism properties. As

1269-746: The Maluku Islands of Indonesia , agar is extracted from Graciliaria and eaten as a type of pickle or a sauce. Jelly seaweeds were also favoured and foraged by Malay communities living on the coasts of the Riau Archipelago and Singapore in Southeast Asia for centuries. 19th century records indicate that dried Graciliaria were one of the bulk exports of British Malaya to China. Poultices made from agar were also used for swollen knee joints and sores in Johore and Singapore. The application of agar as

1316-506: The black and red gulaman used in various fruit salads. In Vietnamese cuisine , 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 , agar is used for making desserts. In Burmese cuisine , a sweet jelly known as kyauk kyaw is made from agar. Agar jelly is widely used in Taiwanese bubble tea . It can be used as addition to (or as

1363-505: The cell walls of certain species of algae and is released on boiling. These algae are known as agarophytes , belonging to the Rhodophyta (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 desserts throughout Asia and also as a solid substrate to contain culture media for microbiological work. Agar can be used as

1410-556: The consumers feeling fuller. One use of agar in Japanese cuisine is in anmitsu , 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 , it is used to make the jelly bars in the various gulaman refreshments like sago't gulaman , samalamig , or desserts such as buko pandan , agar flan , halo-halo , fruit cocktail jelly , and

1457-429: The critical cluster size. In spite of the second law of thermodynamics , crystallization of pure liquids usually begins at a lower temperature than the melting point , due to high activation energy of homogeneous nucleation . The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is expended to form this interface, based on the surface energy of each phase. If

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1504-418: The freezing starts but will continue dropping once it finishes. Crystallization consists of two major events, nucleation and crystal growth . " Nucleation " is the step wherein the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure . " Crystal growth " is the subsequent growth of the nuclei that succeed in achieving

1551-402: 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. Nutrients are typically added to meet the nutritional needs of the microbes organism, the formulations of which may be "undefined" where the precise composition is unknown, or "defined" where the exact chemical composition

1598-477: The gelling agent in gel clarification, a culinary technique used to clarify stocks, sauces, and other liquids. Mexico has traditional candies made out of Agar gelatin, most of them in colorful, half-circle shapes that resemble a melon or watermelon 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

1645-576: The gradient. 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 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 dH 2 O solution

1692-460: The liquid cycle of an autoclave . 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

1739-547: The liquid is poured into molds to be served as desserts and vegetable aspics or incorporated with other desserts such as a layer of jelly in a cake . Agar-agar is approximately 80% dietary fiber , so it can serve as an intestinal regulator. Its bulking quality has been behind fad diets 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

1786-619: 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 , an assistant working in Robert Koch's laboratory, on the suggestion of his wife Fanny Hesse . 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

1833-443: 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

1880-459: 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. Agar consists of a mixture of two polysaccharides : agarose and agaropectin, with agarose making up about 70% of the mixture, while agaropectin makes about 30% of it. Agarose is a linear polymer, made up of repeating units of agarobiose ,

1927-436: 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

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1974-803: The phrase kan -zarashi tokoro ten ( 寒曬心太 ) or "cold-exposed agar"), Japanese isinglass , China grass , Ceylon moss or Jaffna moss . Gracilaria edulis or its synonym G. lichenoides is specifically referred to as agal-agal or Ceylon agar . Macroalgae have been used widely as food by coastal cultures, especially in Southeast Asia . In the Philippines , Gracilaria , known as gulaman (also guraman , gar-garao , or gulaman dagat , among other names) in Tagalog , have been harvested and used as food for centuries, eaten both fresh or sun-dried and turned into jellies. The earliest historical attestation

2021-590: The same rise in temperature. Many living organisms are able to tolerate prolonged periods of time at temperatures below the freezing point of water. Most living organisms accumulate cryoprotectants such as anti-nucleating proteins , polyols, and glucose to protect themselves against frost damage by sharp ice crystals. Most plants, in particular, can safely reach temperatures of −4 °C to −12 °C. Certain bacteria , notably Pseudomonas syringae , produce specialized proteins that serve as potent ice nucleators, which they use to force ice formation on

2068-433: The surface of Petri dishes sown with germinated and/or etiolated seedlings. Experiments with the moss Physcomitrella patens , however, have shown that choice of the gelling agent – agar or Gelrite – does influence phytohormone sensitivity of the plant cell culture . Agar is used: Gelidium agar is used primarily for bacteriological plates. Gracilaria agar is used mainly in food applications. In 2016, AMAM,

2115-442: The surface of various fruits and plants at about −2 °C. The freezing causes injuries in the epithelia and makes the nutrients in the underlying plant tissues available to the bacteria. Three species of bacteria, Carnobacterium pleistocenium , as well as Chryseobacterium greenlandensis and Herminiimonas glaciei , have reportedly been revived after surviving for thousands of years frozen in ice. Many plants undergo

2162-413: 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

2209-422: The uniform liquid. This is a first-order thermodynamic phase transition , which means that as long as solid and liquid coexist, the temperature of the whole system remains very nearly equal to the melting point due to the slow removal of heat when in contact with air, which is a poor heat conductor. Because of the latent heat of fusion , the freezing is greatly slowed and the temperature will not drop anymore once

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