Agar Since 1943 HORACE H. SELBY
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American Agar & Chemical Co., San Diego, Calif.
Agar is of interest to scientists and technologists because of its combination of physical properties. Japan is the largest producer, the Republic of Korea is second, and the United States is third, but several other countries supply considerable quantities. Since about 1870, when agar first became an article of commerce, it has interested scientists and technologists because of the combination of physical properties which characterize i t : low sol gelation temperature, high gel melting temperature, aqueous absorptiveness, gel strength, resilience, gel-forming ability and stability, and physiological inertness. Despite its relatively costly nature, highly purified agar is still widely used in microbiology, dentistry, and medicine and many lower-volume uses are found in industry. Because the War Production Board denied agar to all but bacteriological users during World War II (48), substitutes were actively sought, and suitable agents were found in some instances. Interest in agar has continued at approximately the prewar rate since the work covered by Tseng's excellent review (46), which included many papers published through 1943 and some in 1944. Chemical Abstracts carried some 22 agar items per year in both 1939-41 and 1948-50. Definitions and Specifications It is not surprising that there is no unanimity with respect to definitions of agar, as interest is due to physical properties, and composition, even of purest agar, is apparently variable (2). A step forward was taken in the U . S. Pharmacopeia XIII, which limited the gelation temperature to 32° to 39° C. and the gel melting temperature to 80° or higher at 1.5% concentration, and specified water absorption. The British, Chilean, and Brazilian pharmacopoeias have little in the way of limiting definitions and the word agar has practically no meaning outside the United States, except to signify a gel-forming substance of marine algal origin. The U . S. Pharmacopeia specifications have been revised from time to time, becoming more specific regarding pharmaceutical characteristics. The U . S. Army specification (47), although rather loose and obsolete, is still mentioned. Both the Society of American Bacteriologists (34) and the American ·Public Health Association (13) have committees at work on specifications for agar suitable for use in microbiology. The Jones and Peat polygalactose sulfate formula (23) is frequently quoted as representing agar, despite the evidence of Percival (35) and Barry and Dillon (6) that little, if any, sulfur is an essential constituent. The writer's view (2) is that the presence of sulfur is adventitious at least in Gelidium agar, for it has been removed by elution with aqueous dioxane and aqueous pyridine without loss of identity, whether calcium, potassium, sodium, or ammonium agar is used. Apparently, agar in nature is a calcium polygalactopyranose complex. Agar Studies Hysteresis of sol-gel transformation has been studied (5, 24), as have gelation as a function of age (2, 7), the precipitant action of quaternary ammonium comNATURAL PLANT HYDROCOLLOIDS 16 Advances in Chemistry; American Chemical Society: Washington, DC, 1954.
SELBY—AGAR SINCE 1943
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pounds (54), rheology of agar and other gels (9), hydrolytic and methanolytic products of agar (S), partitioning of ions between gel and syneresis fluid (36), gelation delay and degradation by supersonic energy (18, 55), swelling in dioxane mixtures (12), periodic precipitation confirmation of lyotropic series (15), heat of wetting (11), effect on velocity of eutectic crystallization (4), effect of intensive freezing (37), thermal conductivity (81) the presence of carboxyl (26), polymerization of certain dyes by agar (SO), nutritive value (40), particle solvation (10), and rheopexy (41)·
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Analytical Methods The analytical methods used in Australia have been described by Wood (51). Stoloff and Lee (44) gave methods used in studying 73 samples of national stockpile agar. Methods for gel strength determination have been somewhat improved (2, 32, 42, 43) by both stress-strain and threshold concentration methods. The estimation of metabolically important impurities is a matter of routine in one plant (2), as are control procedures applied to raw material and process operations. The detection of agar in mixtures has had little attention since 1939 (19, 20). Newer Uses Agar has been recommended as an excipient and disintegrating agent in tablets (39) and coffee substitutes, in analytical coagulation of calcium sulfate (27), arsenic sulfide and ferric hydroxide (53), and barium sulfate, as well as in electrophoretic protein separations (17), It is used as a moisture-sensitive membrane in hygrometers, in cosmetic creams, oil-free lubricant jellies, and adhesives, and as a corrosion inhibitor for aluminum. Agar gel is showing promise as an antibiotic carrier in topical medicine and its use in wine clarification is being revived. In foods, agar has recently been used to prepare new piping gels and icings. Little interest in agar substitutes has been found recently. Polyvinyl alcohol and dispersed cellulose (38) and a gum, Gelar, extracted from Baltic Phaeophyceae (25) have been mentioned, as have Chondrus extracts and agaroids (29). Manufacturing Methods The manufacturing techniques employed in certain areas have been briefly described : Australia (28, 51,52) Great Britain (29, 52) Mexico (45) Japan (1, 3, 22, S3, 49) Union of South Africa (14) Florida (50) North Carolina (21) Spain (16) India (8) World Trade Japan maintains her lead in agar manufacture with over 400 plants which produce about 3,000,000 pounds and export 2,000,000 pounds per year. Little highly purified agar is made, however, and the vast majority of the national output is made by the traditional "natural" process. As many as ten new plants have been designed on more modern lines since 1945 with the object of improving quality, but practically all have found operation too costly and the latest intelligence indicates that practically no "scientific" agar is being produced. South Korea exported some 600,000 pounds to Hong Kong in 1952. National production was probably 700,000 pounds. The United States is the third largest producer, with but one factory in daily operation and two on a part-time basis. Annual production approximates 150,000 pounds, most of which is in the highly purified category.
NATURAL PLANT HYDROCOLLOIDS Advances in Chemistry; American Chemical Society: Washington, DC, 1954.
ADVANCES IN CHEMISTRY SERIES
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Gracilaria agar production in Australia, which had reached a peak of 160,000 pounds per year, ceased about 1950. New Zealand produced about 200,000 pounds of Pterocladia agar in 1950, in one factory. Chile has four active plants, which produced 40,000 pounds in 1951. South African production has been quoted as 12,000 pounds. Russian manufacture is rumored to occupy four plants of unknown capacity, which produce agaroid gums. Great Britain has produced various gums resembling agar in some respects with a 10,000-pound annual peak in recent years, dropping to zero in 1952. Mexico produced at a 50,000-pound rate at the height of activity, but both plants are now inactive. Small amounts of agar and agaroids have been made in Italy, Argentina, Scandinavia, India, and Indonesia in the past 5 years. There is no production at present in Canada, India, Ceylon, France, Norway, Sweden, or Israel. Brazil has been reported to have two manufacturers. Three factories in Denmark produced 200,000 pounds of Furcellaria extract in 1951. Portugal produced 60,000 pounds of Gelidium agar in 1951, and Spain produced 250,000 pounds of seaweed extractives including agar. The Chinese industry is probably dormant because of unsettled national economy. Unverified rumors of large production are occasionally heard, however. Literature Cited (1) Adams, M., "The Japanese Agar-Agar Industry," War Dept., Natural Resources Section, Rept. 42 (June 28, 1946). (2) American Agar & Chemical Co., San Diego, Calif., unpublished report. (3) Araki, C., J. Chem. Soc. Japan, 65, 533-8, 627 (1944). (4) Avakyan, S. F . , and Lashko, N . F . , Zhur. Fiz. Khvm., 23, 729-35 (1949). (5) Banerji, S. N., J. Indian Chem. Soc., 22, 161-4 (1945). (6) Barry, V . C., and Dillon, T., Chemistry & Industry, 1944,167. (7) Chakraborty, D., Quart. J. Pharm. Pharmacol., 21, 159-61 (1948). (8) Chakraborty, Q., J. & Proc Inst. Chem. (India), 17, 188-92 (1945). (9) Cheftel, H., and Mocquard, J., J. Soc. Chem. Ind. (London), 66, 297-9 (1947). (10) D'Alcontres, G. S., and Centonze, M., Gazz. chim. ital. 79, 614-20 (1949). (11) Dumanskiĭ, Α. V . , Doklady Akad. Nauk., S.S.S.R., 64, 537-40 (1949). (12) Dumanskiĭ, Α. V . , Mezhenniĭ, Ja. P., and Nekryach, E . F . , Kolloid. Zhur., 10, 193-8 (1948). (13) Fabian, F. W., Michigan State College, private communication, 1951. (14) Fox, F . W., and Stephens, E . , 5. Afrtcan J. Sci., 39, 147-9 (1943). (15) Garbuzov, A . I., Kolloid Zhur., 10, 265-7 (1948). (16) Gomez, F . C., Ion, 43, 5, 105-14 (1945). (17) Gordon, A . H., Keil, B., and Sebasta, K., Nature, 164, 498-9 (1949). (18) Harisaki, Y . , J. Chem. Soc. Japan, 66, 36-7 (1945). (19) Hart, F . D., J. Assoc Office Agr. Chemists, 22, 605-9, 726 (1939). (20) Ibid., 23, 597-603 (1940). (21) Humm, H . J., Science, 96, 230-1 (1942). (22) Japan Agar-Agar Association, "Guide to Japan's Exports," Tokyo, Foreign Trade Press, Ltd., No. 20 (1949). (23) Jones, W . G. M., and Peat, S., J. Chem. Soc., 1942, 225-31. (24) Katti, P., Proc. Indian Acad. Sci., 28A, 216-35 (1948) ; 30A, 35-48 (1949). (25) Kirschninck, H . , Pharmazie, 5, 353-5 (1950). (26) Krajcinovic, M., Arhiv Kem., 20, 122-5 (1948). (27) Lossee, Ε. M . , Can. Chem. Process Inds., 30, No. 11, 90 (1946). (28) Makaroff, Α., Food Inds., 18, 101-3 (1946). (29) Marshal, S. M., Newton, L . , and Orr, A . P., " A Study of Certain British Sea weeds and Their Utilization in the Preparation of Agar," London, Η. M . Stationery Office, 1949. (30) Michaelis, L . , J. Phys. & Colloid Chem., 54, 1-17 (1950). (31) Neiman, Ο. V . , and Neiman, R. E., Kolloid Zhur., 11, 94-7 (1949). (32) Neubern de Toledo, Τ. Α., Anais fac. farm, e odontol. univ. Sâo Paulo, 7, 91-103 (1949). (33) Nippon Kangyo Bank, Ltd., NKB Research Monthly, No. 17 (1950). (34) Pelczar, M . J., University of Maryland, private communication, 1951. NATURAL PLANT HYDROCOLLOIDS Advances in Chemistry; American Chemical Society: Washington, DC, 1954.
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SELBY—AGAR SINCE 1943
(35) Percival, E . G. V . , Nature, 154, 673-7 (1944). (36) Rossi, G., and Nicolini, D., Boll. sci. fac. chim. ind. univ. Bologna, 5, 61-5 (1944-47). (37) Rousselot, Α., Compt. rend., 228, 1334-5 (1949). (38) Ruessbûlt, I., and Faessig, M., Zentr. BakterioL Parasitenk., 151, 285-8 (1944). (39) Sager, H . , Pharm. Acta Helv., 24, 334-9 (1949). (40) Sakurai, Y., and Kato, Y., Nogaku, 1, 184-5 (1949). (41) Sato, K., J. Set. Research Inst. Tokyo, 44, 14-22 (1949). (42) Selby, H . H . , U . S. Fish & Wildlife Service, Fishery Leaflet 118 (1945). (43) Stoloff, L . S., Ibid., 306 (1948). (44) Stoloff, L . S., and Lee, C. F . , Ibid., 335 (1949). (45) Tafall, B. F . O., Ciencia, 7, No. 1-3, 43-56 (1946). (46) Tseng, C. K., Colloid Chemistry, 6, 629-734 (1946). (47) War Dept., U . S. Α., Spec. 4-1041 (1935). (48) War Production Board Limitation Order M-96, amended 6/2/43. (49) Watanabe, K., J. Agr. Chem. Soc. Japan, 17, A69-76 (1941). (50) Williams, R. H . , F l a . Board of Conservation, Educational Series 7, 13-16 (1950). (51) Wood, E . J. F . , Council of Sci. & Ind. Research, Bull 203 (1946). (52) Wood, E . J. F . , Fishing News, London, 7, 8 (June 18, 1949). (53) Yadava, B. P., and Chatterji, A . C., J. Indian Chem. Soc., 21, 227-36 (1944). (54) Yenson, M., Rev. fac. set. univ. Istanbul, 13A, 97-101 (1948). (55) Zhucov, I. I., and Khenokh, Μ. Α., Doklady Akad. Νauk., S.S.S.R., 68, 333-6 (1949). RECEIVED for review November 17, 1952.
Accepted February 4, 1953.
NATURAL PLANT HYDROCOLLOIDS Advances in Chemistry; American Chemical Society: Washington, DC, 1954.
