SC+Agar+&+Carrageenan

Agar (agar-agar) is extracted from seaweed. Agar is a polymer of agarobiose, a disaccharide composed of D-galactose and 3,6-anhydro-L-galactose. Whereas, Carrageenan is a generic term for several polysaccharides also extracted from seaweed. Carrageenan compounds differ from agar in that they have sulfate groups (**-**OSO3-) in place of some hydroxyl groups.
 * 1) **Think about the chemical structure of carrageenan and agar - what do they have in common?**



**2. What are the differences between kappa, iota and lambda carrageenan? Why?**

Comparative properties of types of carrageenan: -

The addition of potassium ions induces the formation of a durable, brittle gel; it also increases the gelling and melting temperatures. Strong, rigid gel, some syneresis, forms helix with K+ ions. Ca++ causes helices to aggregate and the gel to contract and become brittle. Slightly opaque gel. Becomes clear with sugar. Approximately 25% ester sulfate and 34% 3,6-AG Compatible with water miscible solvents Insoluble in most organic solvents Typical use levels — 0.02 to 2.0% || Dilute solutions exhibit thixotropic characteristics Soluble in hot water; sodium iota carrageenan is soluble in cold and hot water The addition of calcium ions will induce the formation of a durable, elastic gel, and increase gelling and melting temperatures. Elastic gels, forms helix with Ca++. Limited aggregation contributes to elasticity, no syneresis. Clear gel Freeze/thaw stable Insoluble in most organic solvents Approximately 32% ester sulfate and 30% 3,6-AG Typical use levels — 0.2 to 2.0% || Free flowing, non-gelling pseudo-plastic solutions in water Partially soluble in cold water, fully soluble in hot water No gel, random distribution of polymer chains Range from low to high viscosity Addition of cations has little effect on viscosity Compatible with water miscible solvents Insoluble in most organic solvents Stable over a wide range of temperatures, including freeze/thaw cycles Soluble in 5% salt solution, hot or cold Approximately 35% ester sulfate and little or no 3,6-AG Typical use level — 0.1 to 1.0% ||
 * Kappa carrageenan || iota carrageenan || lambda carrageenan ||
 * Soluble in hot water

The primary differences which influence the properties of kappa, iota and lambda carrageenan are the number and position of the ester sulfate groups on the repeating galactose units 6. Higher levels of ester sulfate lower the solubility temperature of the carrageenan and produce lower strength gels, or contribute to gel inhibition (lambda carrageenan).