Nonproprietary Names
USP:Acacia JP: Acacia
PhEur:Acacia USP-NF: Acacia
Synonyms
Acaciae gummi; acacia gum; arabic gum; E414; gum acacia; gummi africanum; gum arabic; gummi arabicum; gummi mimosae; talha gum.
Chemical Name and CAS Registry Number
Acacia [9000-01-5]
Empirical Formula and Molecular Weight
Acacia is a complex, loose aggregate of sugars and hemicelluloses with a molecular weight of approximately 240000–580000. The aggregate consists essentially of an arabic acid nucleus to which are connected calcium, magnesium, and potassium along with the sugars arabinose, galactose, and rhamnose.
Structural Formula
See Section 4.
Functional Category
Emulsifying agent; stabilizing agent; suspending agent; tablet binder; viscosity-increasing agent.
Applications in Pharmaceutical Formulation or Technology
Technology Acacia is mainly used in oral and topical pharmaceutical formulations as a suspending and emulsifying agent, often in combination with tragacanth. It is also used in the preparation of pastilles and lozenges, and as a tablet binder, although if used incautiously it can produce tablets with a prolonged disintegration time. Acacia has also been evaluated as a bioadhesive;(1) and has been used in novel tablet formulations,(2) and modified release tablets.(3) See Table I. Acacia is also used in cosmetics, confectionery, food products, and spray-dried flavors.(4) See also Section 18. Table I: Uses of acacia. Use Concentration (%) Emulsifying agent 10–20 Pastille base 10–30 Suspending agent 5–10 Tablet binder 1–5
Description
Acacia is available as white or yellowish-white thin flakes, spheroidal tears, granules, powder, or spray-dried powder. It is odorless and has a bland taste.
Pharmacopeial Specifications
The PhEur 6.3 provides monographs on acacia and spray-dried acacia, while the USP32–NF27 describes acacia in a single monograph that encompasses tears, flakes, granules, powder, and spray-dried powder. The USP32–NF27 also has a monograph on acacia syrup. The JP XV has monographs on acacia and powdered acacia. See Table II. Table II: Pharmacopeial specifications for acacia. Test JP XV PhEur 6.3 USP32–NF27 Identification Characters Microbial limit Water þ þ— 417.0% 415.0%(a) þ þ4104 cfu/g 415.0% 410.0%(b) þ þ þ415.0% — Total ash 44.0% 44.0% 44.0% Acid-insoluble ash 40.5% — 40.5% Insoluble residue 40.2% 40.5% 450 mg/5g Arsenic — — 43 ppm Lead — — 40.001% Heavy metals — — 40.004% Starch, dextrin, and agar Tannin-bearing gums Tragacanth Sterculia gum Glucose and fructose Solubility and reaction — þ— — þ — þ þ þ þ þ — þ þ— — — þ (a) Powdered acacia. (b) Spray-dried acacia.
Typical Properties
Acidity/alkalinity pH = 4.5–5.0 (5% w/v aqueous solution) Acid value 2.5 Hygroscopicity At relative humidities of 25–65%, the equilibrium moisture content of powdered acacia at 258C is 8–13% w/w, but at relative humidities above about 70% it absorbs substantial amounts of water. NIR spectra see Figure 1. Solubility Soluble 1 in 20 of glycerin, 1 in 20 of propylene glycol, 1 in 2.7 of water; practically insoluble in ethanol (95%). In water, acacia dissolves very slowly, although almost completely after two hours, in twice the mass of water leaving only a very small residue of powder. The solution is colorless or yellowish, viscous, adhesive, and translucent. Spray-dried acacia dissolves more rapidly, in about 20 minutes. Specific gravity 1.35–1.49 Viscosity (dynamic) 100mPas (100cP) for a 30% w/v aqueous solution at 208C. The viscosity of aqueous acacia solutions varies depending upon the source of the material, processing, storage conditions, pH, and the presence of salts. Viscosity increases slowly up to about 25% w/v concentration and exhibits Newtonian behavior. Above this concentration, viscosity increases rapidly (non-Newtonian rheology). Increasing temperature or prolonged heating of solutions results in a decrease of viscosity owing to depolymerization or particle agglomeration. See also Section 12. 1 1100 1300 1500 1700 1900 2100 2300 2500 Wavelength/nm Figure 1: Near-infrared spectrum of acacia measured by reflectance.
Stability and Storage Conditions
Aqueous solutions are subject to bacterial or enzymatic degradation but may be preserved by initially boiling the solution for a short time to inactivate any enzymes present; microwave irradiation can also be used.(5) Aqueous solutions may also be preserved by the addition of an antimicrobial preservative such as 0.1% w/v benzoic acid, 0.1% w/v sodium benzoate, or a mixture of 0.17% w/v methylparaben and 0.03% propylparaben. Powdered acacia should be stored in an airtight container in a cool, dry place.
Incompatibilities
Acacia is incompatible with a number of substances including amidopyrine, apomorphine, cresol, ethanol (95%), ferric salts, morphine, phenol, physostigmine, tannins, thymol, and vanillin. An oxidizing enzyme present in acacia may affect preparations containing easily oxidizable substances. However, the enzyme may be inactivated by heating at 1008C for a short time; see Section 11. Many salts reduce the viscosity of aqueous acacia solutions, while trivalent salts may initiate coagulation. Aqueous solutions carry a negative charge and will form coacervates with gelatin and other substances. In the preparation of emulsions, solutions of acacia are incompatible with soaps.
Method of Manufacture
Acacia is the dried gummy exudate obtained from the stems and branches of Acacia senegal (Linne´) Willdenow or other related species of Acacia (Fam. Leguminosae) that grow mainly in the Sudan and Senegal regions of Africa. The bark of the tree is incised and the exudate allowed to dry on the bark. The dried exudate is then collected, processed to remove bark, sand, and other particulate matter, and graded. Various acacia grades differing in particle size and other physical properties are thus obtained. A spray-dried powder is also commercially available.
Safety
Acacia is used in cosmetics, foods, and oral and topical pharmaceutical formulations. Although it is generally regarded as an essentially nontoxic material, there have been a limited number of reports of hypersensitivity to acacia after inhalation or ingestion.(6,7) Severe anaphylactic reactions have occurred following the parenteral administration of acacia and it is now no longer used for this purpose.(6) The WHO has not set an acceptable daily intake for acacia as a food additive because the levels necessary to achieve a desired effect were not considered to represent a hazard to health.(8) LD50 (hamster, oral): >18g/kg(9) LD50 (mouse, oral): >16g/kg LD50 (rabbit, oral): 8.0g/kg LD50 (rat, oral): >16g/kg
Handling Precautions
Observe normal precautions appropriate to the circumstances and quantity of material handled. Acacia can be irritant to the eyes and skin and upon inhalation. Gloves, eye protection, and a dust respirator are recommended.
Regulatory Status
GRAS listed. Accepted for use in Europe as a food additive. Included in the FDA Inactive Ingredients Database (oral preparations and buccal or sublingual tablets). Included in the Canadian List of Acceptable Non-medicinal Ingredients. Included in nonparenteral medicines licensed in the UK. 17 Related Substances Ceratonia; guar gum; tragacanth.
Comments
Concentrated aqueous solutions are used to prepare pastilles since on drying they form solid rubbery or glasslike masses depending upon the concentration used. Foreign policy changes and politically unstable conditions in Sudan, which is the principal supplier of acacia, has created a need to find a suitable replacement.(10) Poloxamer 188 (12–15% w/w) can be used to make an oil/water emulsion with similar rheological characteristics to acacia. Other natural by-products of foods can also be used.(11) Acacia is also used in the food industry as an emulsifier, stabilizer, and thickener. A specification for acacia is contained in the Food Chemicals Codex (FCC).(12) The EINECS number for acacia is 232-519-5. 19 Specific References 1 Attama AA et al. Studies on bioadhesive granules. STP Pharma Sci 2003; 13(3): 177–181. 2 Streubel A et al. Floating matrix tablets based on low density foam powder: effects of formulation and processing parameters on drug release. Eur J Pharm Sci 2003; 18: 37–45. 3 Bahardwaj TR et al. Natural gums and modified natural gums as sustained-release carriers. Drug Dev Ind Pharm 2000; 26(10): 1025– 1038. 4 Buffo R, Reineccius G. Optimization of gum acacia/modified starch/ maltodextrin blends for spray drying of flavors. Perfumer & Flavorist 2000; 25: 45–54. 5 Richards RME, Al Shawa R. Investigation of the effect of microwave irradiation on acacia powder. J Pharm Pharmacol 1980; 32: 45P. 6 Maytum CK, Magath TB. Sensitivity to acacia. J Am Med Assoc 1932; 99: 2251. 7 Smolinske SC. Handbook of Food, Drug, and Cosmetic Excipients. Boca Raton, FL: CRC Press, 1992; 7–11. 8 FAO/WHO. Evaluation of certain food additives and contaminants. Thirty-fifth report of the joint FAO/WHO expert committee on food additives. World Health Organ Tech Rep Ser 1990; No. 789. 9 Lewis RJ, ed. Sax’s Dangerous Properties of Industrial Materials, 11th edn. New York: Wiley, 2004; 289. 10 Scheindlin S. Acacia – a remarkable excipient: the past, present, and future of gum arabic. JAMA 2001; 41(5): 669–671. 11 I-Achi A et al. Experimenting with a new emulsifying agent (tahini) in mineral oil. Int J Pharm Compound 2000; 4(4): 315–317. 12 Food Chemicals Codex, 6th edn. Bethesda, MD: United States Pharmacopeia, 2008; 425.
General References
Anderson DMW, Dea ICM. Recent advances in the chemistry of acacia gums. J Soc Cosmet Chem 1971; 22: 61–76. Acesulfame Potassium 3 Anderson DM et al. Specifications for gum arabic (Acacia Senegal):
Author
analytical data for samples collected between 1904 and 1989. Food AH Kibbe. Add Contam 1990; 7: 303–321. Aspinal GO. Gums and mucilages. Adv Carbohydr Chem Biochem 1969; 24: 333–379.
Date of Revision
Whistler RL. Industrial Gums. New York: Academic Press, 1959. 10 February 2009.