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Agar Excipient | Uses, Suppliers, and Specifications
Agar is a heterogenous polysaccharide mainly composed of the monomeric substances D-galactose and (3,6)-anhydro-L-galactose. It is the structural building component of the cell walls of red algae. The main chemical substance, which is responsible for the strong gelling ability of agar, is agarose. It also contains a small amount of agaropectin. Agar is supplied as transparent, odourless, tasteless strips or as a coarse or fine powder.
Pharmacopoeial Compliance: USP-NF; Ph.Eur; B.P; J.P; I.P
Synonyms and Trade Names: Agar-Agar; Agar-Agar Flake; Agar-Agar Gum; Bengal Gelatin; Bengal Gum; Bengal Isinglass; Ceylon Isinglass; Chinese Isinglass; E406; Gelosa; Japan Agar; Japan Isinglass
Uses and Applications: Emulsifying Agent; Stabilizing Agent; Suppository Base; Suspending Agent; Sustained-Release Agent; Tablet Binder; Thickening Agent And Viscosity-Increasing Agent
Agar-Agar - PharmaCentral.com
Description
Agar (also known as Agar-Agar) is the name for a complex class of naturally-occurring polysaccharide substances obtained from the agarocytes of certain strains of marine algae of the families Gelidiaceae and Gracilariaceae and relevant red algae of the class Rhodophyceae. It is a structure-building component of the algae cell wall.
Chemically, Agar is a composite of two galactose-based polysaccharides composed of the monomeric substances D-galactose and (3,6)-anhydro-L-galactose. There are three extremes of structure noted: namely neutral agarose; pyruvated agarose having little sulfation; and a sulfated galactan, agaropectin. Agarose, which is the main component polymer of Agar is highly gelling. The D-galactose and 3,6)-anhydro-L-galactose are believed to be linked alternately by α-(1,3) and β-(1,4) bonds. Owing to the high anhydrogalactose portion, agar exhibits strong gelling properties that are independent of cations.
Agar has a long history of use in food products, and more particularly in Asian cuisine. It is among the first hydrocolloid to be discovered and industrialised. It was discovered in 1658 by a Japanese worker who observed gelling in a seaweed soup during winter. It was subsequently commercialised as a dry and versatile product in Japan at the start of the 18th century, and introduced into the West in the 20th century.
Currently, the main producing countries are Japan, the United States of America, Chile, and Spain. The production process can be summarised in a series of steps, as shown below:
Agar occurs as transparent, odourless, tasteless strips or as a coarse or fine powder. It may also be slightly yellowish-orange, yellowish-grey to pale-yellow coloured, or colourless material. Agar is tough when damp but brittle when dry.
Chemical Structure & Identifiers
| Chemical Name | Agar |
| CAS Registry Number | [9002-08-0] |
| Empirical Formula | C12H20O10(C12H18O9)n |
| Molecular Weight | 80 000 – 140 000 g/mol |
| EC Number | 232-658-1 |
| UNII Code (US FDA) | 3PBT7NM2M0 |
Regulatory Status
Agar is an approved pharmaceutical excipient. It is currently listed in all major pharmacopoeia, including the USP-NF and the Ph.Eur. It is also GRAS listed and generally regarded as relatively nontoxic and nonirritant when used as an excipient. Accepted for use as a food additive in Europe (E406) and included in the FDA Inactive Ingredients Database (covering oral tablets).
Physicochemical Properties
| Physical form | Solid |
| Colour | Transparent strips or fine/course powder |
| Odour | Odourless |
| Solubility | Agar-agar is insoluble in cold water, but it swells considerably, absorbing as much as twenty times its own weight of water. It dissolves readily in boiling water and sets to a firm gel at concentrations as low as 0.50%. Powdered dry agar-agar is soluble in water and other solvents at temperatures between 95º to 100º C. Moistened agar flocculated by ethanol, 2-propanol or acetone, or salted out by high concentrations of electrolytes, is soluble in a variety of solvents at room temperature. Special types of agar-agar that passes through additional processes are soluble at lower temperatures between 85º to 90º C. |
| Viscosity | 18 – 20 mPas. Viscosity depends on temperature and pH. The viscosity of agar solutions varies widely and is markedly dependent upon the raw material source. The viscosity of an agar solution at temperatures above its gelling point is relatively constant at pHs 4.5 to 9.0, and is not greatly affected by age or ionic strength within the pH range 6.0 to 8.0. However, once gelling starts viscosity at constant temperature increases with time. |
| Gelling temperature | 50 oC |
| Melting point | 75 – 85 oC |
| Gel strength | 145 ± 35 g/cm2 |
Pharmacopeoeal Specifications
| USP-NF | Ph.Eur | J.P | |
| Official name | Agar | Agar | Agar |
| Authorised use | Excipient | Excipient | Excipient |
| Definition | specified | specified | specified |
| Identification | specified | specified | specified |
| Characters | n/a | specified | specified |
| Swelling index | n/a | specified | n/a |
| Arsenic | ≤3 ppm | n/a | n/a |
| Lead | ≤0.001% | n/a | n/a |
| Sulfuric acid | n/a | n/a | specified |
| Sulfurous acid and starch | n/a | n/a | specified |
| Gelatin | specified | specified | n/a |
| Heavy metals | ≤0.004% | n/a | n/a |
| Insoluble matter | ≤15.0mg | ≤1.0% | ≤15.0mg |
| Water absorption | ≤75mL | n/a | ≤75mL |
| Loss on drying | ≤20.0% | ≤20.0% | ≤22.0% |
| Microbial contamination | specified | ≤103 cfu/g(a) | n/a |
| Total ash | ≤6.5% | ≤5.0% | ≤4.5% |
| Acidn/ainsoluble ash | ≤0.5% | n/a | ≤0.55 |
| Foreign organic matter | ≤1.0% | n/a | n/a |
| Limit of foreign starch | specified | n/a | n/a |
| Assay | n/a | n/a | n/a |
| Labelling | n/a | n/a | n/a |
Key: n/a Specification is not listed
*All claims with respect to conformity are subject to our Terms and Conditions. No express or implied warranty is made for specific properties or fitness for any particular application or purpose.
Applications in Pharmaceutical Formulations or Technology
Agar is a versatile pharmaceutical excipient that serves in a number of functional capacities including the use as an emulsifying agent, stabilizing agent, suppository base, suspending agent, sustained-release agent, tablet binder, thickening agent and viscosity-increasing agent. However, versatility has not translated into wide usage.
Solid dosage forms
Instead, Agar is used in only a handful of oral tablets and topical formulations. Nevertheless, it has also been investigated in a number of experimental pharmaceutical applications including as a sustained-release agent in gels, beads, microspheres, and tablets. Agar is also reported to function as a disintegrant in solid dosage forms.
Agar has been utilised in the design of a floating controlled-release tablet; with the dosage form’s buoyancy being provided, in part, by the air trapped in the agar gel network.
Other applications
Agar can be used as a viscosity-increasing agent in aqueous preparations. It has reportedly been used as a foundation for non-melting and non-disintegrating suppositories. Agar has an important role as a suspending agent in pharmaceutical suspensions.
The ability to form reversible gels by simply cooling hot, aqueous solutions is the most important property of Agar. This gel-forming ability has led to a large number of practical applications, particularly in the food sector as a food additive as well as several other applications in microbiology, biochemistry and molecular biology. There are also several industrial applications that make use of the gelling properties of Agar.
Regarding its gelling properties, Agar exhibits unique properties compared with other hydrocolloids. These are outlined below as follows:
- Ability to form gels in very dilute solutions (0.5% to 1.0% of Agar). The obtained gels are rigid and brittle with sharp melting and gelling points.
- Furthermore, the gels display both syneresis and hysteresis phenomena. Gelling occurs at temperatures far below the gel melting temperature. A 1.5% solution of Agar forms a gel on cooling to about 32 to 45 ºC that does not melt below 85 ºC. This hysteresis interval is a unique property of Agar that is useful in food applications.
- The gel strength of the Agar is influenced by concentration, time, pH, and sugar content. As the pH decreases, the gel strength weakens. Sugar content has also a considerable effect on gels. Generally, increasing levels of sugar creates gels with harder but less cohesive texture.
- Agar has no taste and smell.
Safety and Precautions
Agar is an authorised additive in a wide range of foods although its usage is limited to only a few food categories. Agar has been evaluated by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the European Food Safety Authority, who concluded that there was no need for a numerical ADI for Agar and that there were no safety concerns for the general population at the refined exposure assessment for the reported uses of agar as a food additive.
Following oral ingestion, Agar is not digested or absorbed systemically. It is fermented by colon microbiota to a limited extent. Toxicity data available to date have raised no concerns with respect to the genotoxicity and carcinogenicity. Oral intake of agar (4,500 mg/person corresponding to 64 mg/kg bw per day) was tolerated in humans for 12 weeks without noticeable side effects
Toxicology: LD50 (rat, oral): 11.0g/kg
Stability and Storage Conditions
Agar is a stable excipient when correctly stored (in a cool, dry, place). The assigned shelf life is 24-36 months, depending on the manufacturer. Empty containers may represent a dust hazard due to the presence of product residues (dust and solids). Therefore, observe applicable SHEQ protocols relevant to the circumstances and quantity of the material processed.
Sustainability and Environmental Impact
Agar has a long history of use in food applications, particularly in Asian cuisine. Agar is a natural and biodegradable polysaccharide whose production is relatively sustainable since there is no known long term damage to the environment or marine ecology.
Manufacturers & Suppliers
Sobigel
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