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Mizuyōkan - a popular Japanese red bean jelly made from agar

Agar or agar agar is a gelatinous substance derived from seaweed. Historically and in a modern context, it is chiefly used as an ingredient in desserts throughout Japan, but in the past century has found extensive use as a solid substrate to contain culture medium for microbiological work. The gelling agent is an unbranched polysaccharide obtained from the cell walls of some species of red algae, primarily from the genera Gelidium and Gracilaria, or seaweed (Sphaerococcus euchema). Commercially it is derived primarily from Gelidium amansii.

Agar (agar agar) can be used as a laxative, a vegetarian gelatin substitute, a thickener for soups, in jellies, ice cream and Japanese desserts such as anmitsu, as a clarifying agent in brewing, and for paper sizing fabrics.

Chemically, agar is a polymer made up of subunits of the sugar galactose. Agar polysaccharides serve as the primary structural support for the algae's cell walls.

Contents

Names

The word "agar" comes from the Malay word agar-agar (meaning jelly). It is also known as kanten, China grass, or Japanese isinglass. The various species of alga or seaweed from which agar is derived are sometimes called Ceylon moss. Gracilaria lichenoides specifically is referred to as agal-agal or Ceylon agar.[1]

In Malay and Indonesian, it is known as agar-agar. In Japanese, it is known as kanten (寒天) meaning "cold weather," referring to the fact that it is harvested in the winter months. In Mandarin Chinese as hǎicài (海菜) meaning "ocean vegetable", hǎizàoqióngzhī (海藻瓊脂) or dòngfěn (凍粉). In Taiwanese Hokkien it is known as chhài-iàn (菜燕) meaning "vegetable swiftlet," i.e., similar in texture to the nest of the edible-nest swiftlet used in bird's nest soup. In Korea, it is known as hancheon (한천). In the Philippines, it is known as gulaman in Tagalog, Apayao, Bikol, and Pangasinan, guraman in Ilokano and gurguraman in Sambali.[2] In Thai it is known as wóon (วุ้น). In Tamil and Telugu it's called as paal kasuv.

Structure

Agar consists of a mixture of agarose and agaropectin. Agarose is a linear polymer, of molecular weight about 120,000, based on the -(1->3)-β-D-galactopyranose-(1->4)-3,6-anhydro-α-L-galactopyranose unit, the major differences from carrageenans being the presence of L-3,6-anhydro-α-galactopyranose rather than D-3,6-anhydro-α-galactopyranose units and the lack of sulfate groups. Agaropectin is a heterogeneous mixture of smaller molecules that occur in lesser amounts. Their structures are similar but slightly branched and sulfated, and they may have methyl and pyruvic acid ketal substituents. They gel poorly and may be simply removed from the excellent gelling agarose molecules by using their charge. The quality of agar is improved by alkaline treatment that converts of any L-galactose-6-sulfate to 3,6-anhydro-L-galactose.

Agarose molecules have molecular weights of about 120,000. The gel network of agarose contains double helices formed from left-handed threefold helices. These double helices are stabilized by the presence of water molecules bound inside the double helical cavity [508]. Exterior hydroxyl groups allow aggregation of up to 10,000 of these helices to form suprafibers.[3]

Properties

Agar exhibits hysteresis, melting at 85 °C (358 K, 185 °F) and solidifying from 32-40 °C (305-313 K, 90-104 °F).[4]

Microbiology

100mm diameter petri dishes containing agar jelly for bacterial culture

Nutrient agar is used throughout the world to provide a solid surface containing medium for the growth of bacteria and fungi. 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. Though less than 1% of all existing bacteria can be grown successfully,[citation needed] the basic agar formula can be used to grow most of the microbes whose needs are known. More specific nutrient agars are available, because some microbes prefer certain environmental conditions over others.

Motility assays

As a gel, an 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 only show growth 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.

Molecular biology

The structure of an agarose polymer.

Agar is a heterogeneous mixture of two classes of polysaccharide: agaropectin and agarose.[5] Although both polysaccharide classes share the same galactose-based backbone, agaropectin is heavily modified with acidic side-groups, such as sulfate and pyruvate. The neutral charge and lower degree of chemical complexity of agarose make it less likely to interact with biomolecules, such as proteins. Gels made from purified agarose have a relatively large pore size, making them useful for size-separation of large molecules, such as proteins or protein complexes >200 kilodaltons, or DNA fragments >100 basepairs. Agarose can be used for electrophoretic separation in agarose gel electrophoresis or for column-based gel filtration chromatography.

Agar plates are commonly supplemented with antibiotics for use selecting bacteria expressing plasmids. Commonly used antibiotics include: ampicillin (final concentration = 100 micrograms/ml); kanamycin (final concentration = 50 micrograms/ml).

Plant biology

Physcomitrella patens plants growing axenically in vitro on agar plates (Petri dish, 9 cm diameter).

Research grade agar is used extensively in plant biology as it is supplemented with a nutrient and vitamin mixture that allows for seedling germination in petri dishes under sterile conditions (given that the seeds are sterilized as well). Nutrient and vitamin supplementation for Arabidopsis thaliana is standard across most experimental conditions. Murashige & Skoog (MS) nutrient mix and Gamborg's B5 vitamin mix are generally used. A 1.0% agar/0.44% MS+vitamin dH20 solution is suitable for growth media between normal growth temps.

The solidification of the agar within any growth media (GM) is pH-dependent, with an optimal range between 5.4-5.7. Usually, the application of KOH 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.

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 Physcomitrella patens, however, have shown that choice of the gelling agent — agar or Gelrite - does influence phytohormone sensitivity of the plant cell culture.[6]

Culinary

Agar-Agar is a natural vegetable gelatin counterpart originally eaten in Japan. White and semi-translucent, it is sold in packages as washed and dried strips or in powdered form. It can be used to make jellies, puddings and custards. For making jelly, it is boiled in water until the solids dissolve. One then adds sweetener, flavouring, colouring, fruit or vegetables, and pours the liquid into molds to be served as desserts and vegetable aspics, or incorporated with other desserts, such as a jelly layer on a cake.

Agar-agar is approximately 80% fiber, so it can serve as an intestinal regulator. Its bulk quality is behind one of the latest fad diets in Asia, the kanten diet. Once ingested, kanten triples in size and absorbs water. This results in the consumer feeling more full. Recently this diet has received some press coverage in the United States as well. The diet has shown promise in obesity studies.[7]

One use of agar in Japanese cuisine is 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 Mizuyōkan, another popular Japanese food. (See very top image.) In Indian cuisine, agar agar is known as "China grass" and is used for making desserts. In Burmese cuisine, a sweet jelly known as kyauk kyaw (​ေကျာက်​ေကြာ [tʃaoʔtʃau]) is made from agar.

Other uses

Agar is used:

See also

References

  1. ^ Agar-Agar at Botanical.com
  2. ^ Gulaman at Bureau of Plant Industry website
  3. ^ Agar at lsbu.ac.uk Water Structure and Science
  4. ^ http://www.sciencebuddies.org/science-fair-projects/project_ideas/MicroBio_Agar.shtml
  5. ^ FAO agar manual
  6. ^ Birgit Hadeler, Sirkka Scholz, Ralf Reski. "Gelrite and agar differently influence cytokinin-sensitivity of a moss". Journal of Plant Physiology 146: 369-371. 
  7. ^ Maeda H, Yamamoto R, Hirao K, Tochikubo O (January 2005). "Effects of agar (kanten) diet on obese patients with impaired glucose tolerance and type 2 diabetes". Diabetes, Obesity, and Metabolism 7 (1). PMID 15642074. 

Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also agar

Spanish

Proper noun

Agar

  1. Hagar (Biblical character)

Quotations

  • 1602La Santa Biblia (antigua versión de Casiodoro de Reina), rev., Génesis 16:15
    Y parió Agar á Abram un hijo, y llamó Abram el nombre de su hijo que le parió Agar, Ismael.

Bible wiki

Up to date as of January 23, 2010
(Redirected to Hagar article)

From BibleWiki

Meaning: flight, or, according to others, stranger

An Egyptian, Sarah's handmaid (Gen 16:1; 21:9, 10), whom she gave to Abraham as a secondary wife (16:2). When she was about to become a mother she fled from the cruelty of her mistress, intending apparently to return to her relatives in Egypt, through the desert of Shur, which lay between. Wearied and worn she had reached the place she distinguished by the name of Beer-lahai-roi ("the well of the visible God"), where the angel of the Lord appeared to her. In obedience to the heavenly visitor she returned to the tent of Abraham, where her son Ishmael was born, and where she remained (16) till after the birth of Isaac, the space of fourteen years. Sarah after this began to vent her dissatisfaction both on Hagar and her child. Ishmael's conduct was insulting to Sarah, and she insisted that he and his mother should be dismissed. This was accordingly done, although with reluctance on the part of Abraham (Gen 21:14). They wandered out into the wilderness, where Ishmael, exhausted with his journey and faint from thirst, seemed about to die. Hagar "lifted up her voice and wept," and the angel of the Lord, as before, appeared unto her, and she was comforted and delivered out of her distresses (Gen 21:18, 19).

Ishmael afterwards established himself in the wilderness of Paran, where he married an Egyptian (Gen 21:20,21).

"Hagar" allegorically represents the Jewish church (Gal 4:24), in bondage to the ceremonial law; while "Sarah" represents the Christian church, which is free.

This entry includes text from Easton's Bible Dictionary, 1897.

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Contents

—Biblical Data:

Egyptian handmaid of Sarah, and mother of Ishmael. According to one narrative, Sarah, having no children, requested Abraham to take Hagar as concubine, so that she might adopt her children (comp. Gen 30:3, where Rachel makes a similar request). When Hagar had conceived she became domineering, and Sarah, with the consent of Abraham, drove her into the wilderness. There, as she sat by a fountain, an angel of the Lord appeared and commanded her to return to her mistress and submit to her. He promised that she should bear a son who would be called "Ishmael" (= "he whom the Lord will hear"), and that he would be a strong fighter ("a wild ass among men"), and would be respected by his brethren (Gen. xvi.). Another narrative tells that when Isaac had been weaned Ishmael "played" with him or "mocked" him ( (missing hebrew text) is ambiguous), and that Sarah demanded of Abraham that he cast out Hagar and her son, that the latter might not inherit with Isaac. Abraham was unwilling to do so, but upon God's command he yielded. Hagar fled again into the wilderness, where Ishmael came near dying of thirst. In the moment of her greatest despair an angel of God appeared to her and showed her a well, promising her that Ishmael would found a great nation. She dwelt with her son in the wilderness of Paran, where he became an archer, and she took a wife for him from Egypt (Gen 21:9-21).

Only one other mention of Hagar is found in the Bible (Gen 25:12), where she is merely referred to as the mother of Ishmael. There are in various passages in Chronicles, however, references to the tribe of Hagarites, who were neighbors of the transJordanic tribes of Israel and were driven from their homes by them (1Chr 5:10, 18-22; xi. 38; xxvii. 31). The Hagarites have been identified with the Agraioi mentioned by Strabo (xvi. 4, 2), and though Arabians, they do not belong to the Ishmaelites.

Bibliography: Dillmann, Die Genesis, 6th ed., p. 315, Leipsic, 1892; Herzog-Hauck, Real-Encyc. s.v.

—In Rabbinical Literature:

According to the Midrash (Gen. R. xlv.), Hagar was the daughter of Pharaoh, who, seeing what great miracles God had done for Sarah's sake (Gen 12:17), said: "It is better for Hagar to be a slave in Sarah's house than mistress in her own." In this sense Hagar's name is interpreted as "reward" ("Ha-Agar" = "this is reward"). She was at first reluctant when Sarah desired her to marry Abraham, and although Sarah had full authority over her as her handmaid, she persuaded her, saying. "Consider thyself happy to be united with this saint." Hagar is held up as an example of the high degree of godliness prevalent in Abraham's time, for while Manoah was afraid that he would die because he had seen an angel of God (Jdg 13:22), Hagar was not frightened by the sight of the divine messenger (Gen. R. l.c.). Her fidelity is praised, for even after Abraham sent her away she kept her marriage vow, and therefore she was identified with Keturah (Gen 25:1), with allusion to (missing hebrew text) (Aramaic, "to tie"; Gen. R. lxi.). Another explanation of the same name is "to adorn," because she was adorned with piety and good deeds (l.c.). It was Isaac who, after the death of Sarah, went to bring back Hagar to the house of his father; the Rabbis infer this from the report that Isaac came from Beer-lahai-roi, the place which Hagar had named (Gen 16:14, xxiv. 62; Gen. R. lx.; see commentaries ad loc.).

Other homilies, however, take an unfavorable view of Hagar's character. Referring to the report that when she had conceived she began to despise her mistress, the Rabbis say that she gossiped about Sarah, saying: "She is certainly not as godly as she pretends to be, for in all the years of her married life she has had no children, while I conceived at once" (Gen. R. xlv.; Sefer ha-Yashar, Lek Leka). Sarah took revenge (Gen. xvi.) by preventing her intercourse with Abraham, by whipping her with her slipper, and by exacting humiliating services, such as carrying her bathing-materials to the bath (l.c.);she further caused Hagar by an evil eye to miscarry, and Ishmael, therefore, was her second child, as is inferred from the fact that the angel prophesied that she would bear a child (Gen 16:11), while it had been narrated before that she was pregnant (Gen 16:4). It is further inferred, from the words "she went astray" (Gen 21:14, Hebr.), that as soon as she had reached the wilderness she relapsed into idolatry, and that she murmured against God's providence, saying: "Yesterday thou saidest: 'I will multiply thy seed exceedingly' [[[Book of Genesis|Gen]] 16:10]; and now my son is dying of thirst." The fact that she selected an Egyptian woman as her son's wife is also counted against her as a proof that her conversion to Judaism was not sincere, for "throw the stick into the air, it will return to its root" (Gen. R. liii., end). This Egyptian wife is explained in the Targum of pseudo-Jonathan to refer to Khadijaand Fatima, the widow and the daughter of Mohammed (see Zunz, "G. V." 2d ed., p. 288, note a).

Bibliography: Yalḳuṭ, Genesis, 79, 80, 95.

—Critical View:

While the two narratives, Gen. xvi. and xxi. 9-21, are not directly contradictory, the critical school, pointing to the fact that in both instances Hagar is expelled upon Sarah's request and with the reluctant assent of Abraham, and that in both instances she receives, while sitting by a fountain, a divine message foretelling the great destiny of her son, finds in these narratives two parallel accounts of the origin of the Bedouins, whose racial affinity with the Israelites the latter had to admit, while degrading them by tracing their origin to a concubine of their common ancestor. Accordingly the name "Hagar" is explained as "the fugitive," from the Arabic "hajar" (to flee). Her native country was not Egypt, but Muṣri in northern Arabia, according to Winckler ("Altorientalische Forschungen," pp. 29 et seq., as cited by Holzinger, "Genesis," in "Kurzer Hand-Commentar zum Alten Testament," p. 151). As regards sources, the account in Gen. xvi. is assumed to be Jahvistic, with the exception of verse three, which, apparently repeating verse two, is ascribed to the Priestly Code; the account in Gen. xxi. is put down as Elohistic.

Bibliography: The commentaries on Genesis by Dillmann, Delitzsch, and Holzinger: Herzog-Hauck, Real-Encyc.

—In Arabic Literature:

According to the Midrash (Gen. R. xlv.), Hagar was the daughter of Pharaoh, who presented her to Abraham. The same story is told in Mohammedan tradition. When she bore Ishmael, from whose countenance the light of Mohammed shone forth, Sarah demanded her expulsion. Abraham desired to spare her, but Sarah swore to bathe her hands in her rival's blood. Abraham thereupon pierced Hagar's car and caused the blood to run over Sarah's hand, that her vow might be fulfilled without sacrificing Hagar's life. When Isaac was born Sarah's jealousy awoke afresh, and she insisted that Hagar should go. Conducted by the archangel Gabriel, Abraham took Hagar and Ishmael into the Arabian desert, and left them at the place where the Kaaba of Mecca was built later on. As soon as Hagar's scant provisions were exhausted she sought water, running and praying, between the hills Safa and Marwah. This she repeated seven times. At last the archangel Gabriel reappeared, and, stamping his foot on the ground, brought forth a spring. This is the holy fountain of Zamzam, near the Kaaba. In commemoration of Hagar's example, running seven times between the two hills mentioned above has been made an important ceremony in the pilgrimage to Mecca. As the spring provided Hagar and Ishmael with water, they remained there, and Abraham visited them every month. When Ishmael was thirteen years old Abraham was told in a dream to sacrifice him. Satan, however, appeared to Hagar and asked her: "Dost thou know whither Abraham went with thy son?" "Yes," she replied; "he went into the forest to cut wood." "No," said Satan; "he went to slaughter thy son." "How can that be," asked Hagar, "since he loves him as much as I do?" "He believes," Satan answered, "that God has commanded him to do so." "If this be so," said Hagar, "let him do the will of God."

This entry includes text from the Jewish Encyclopedia, 1906.
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Simple English

The word agar comes from the Malay word agar-agar (meaning jelly). Chemically comes from agarose. It is obtained from red algae Gellidium and Gracillaria. It is used as a place to grow bacteria in an microbiology laboratory, and to make some foods thicker, like soup.

Reference








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