234 MARINE FISHERIES OF NORTH CAROLINA 



RED ALGAE 



Agar and agar-like substances (agaroids) are the important extractives 

 of red seaweeds. Agar is manufactured on both the Atlantic and Pacific 

 coasts of the United States. The agaroid, carrageenin, is obtained from 

 the seaweed, "Irish moss," along the coasts of the New England states and 

 Canada. A potential source of another agaroid is the seaweed Agardhiella, 

 abundant in the spring along the North Carolina coast. 



Before World War II, Japan had almost a monopoly on agar of com- 

 merce, and 90 per cent of the agar consumed in the United States was 

 imported from Japan. Consequently, Allied nations were without an ade- 

 quate source of agar when hostilities began. Early in 1942, agar was classi- 

 fied by the War Production Board as a "critical war material" and its use 

 restricted to bacteriological purposes. As a result, both governmental agen- 

 cies and private institutions were stimulated to support a search for hitherto 

 undiscovered sources of agar raw material and to look for agar substitutes. 

 One outcome was the development of the agar industry in North Carolina. 



CHEMICAL NATURE AND PHYSICAL PROPERTIES OF AGAR 



Agar is the gel-forming extractive of Gelidium, Gracilaria, and certain 

 other red seaweeds, a one per cent solution of which in water forms a firm 

 gel. Chemically it is a complex carbohydrate described as the sulfuric acid 

 ester of a linear galactan. In hot water (80° C. or above), dehydrated agar 

 forms a colloidal solution. Gelation occurs at about 40° C, although some 

 Gracilaria agar may gel as high as 63°. The gel strength of agar is about 

 eight times that of gelatin so that in culture media where a 1.5 per cent 

 concentration of agar forms an adequate gel, 12 per cent gelatin is needed 

 to obtain a semi-solid medium of the same strength. 



Agar is a cell wall constituent, along with cellulose, of the seaweeds in 

 which it occurs, where it probably functions to control diffusion of solutes 

 into and out of the cell, to reduce loss of water if the plant is exposed at 

 low tide, and it may serve as a reserve food. It exists as the calcium (or 

 other metal) salt of the polysaccharide galactan. By means of electro- 

 dialysis the metallic ions may be removed from agar leaving free agar acid 

 which may then be neutralized with any base, forming a metallic or ammo- 

 nium agarinate. When agar is hydrolyzed by heating with dilute acid, 

 galactose is the principal sugar produced. 



USES OF AGAR 



The most important use of agar, with respect to human welfare, is in 

 bacteriological culture media, although there are several other uses equally 



