These chemicals are large, highly flexible molecules which curl around eachother forming double-helical structures. This gives them the ability to form a variety of different gels at room temperature. They are widely used in the food and other industries as thickening and stabilising agents. A particular advantage is that they are thixotropic—they thin under shear stress and recover their viscosity once the stress is removed. This means that they are easy to pump but stiffen again afterwards.
For example, they can be used in:
When used in food products, carrageenan has the EU additive E-number E407. Although introduced on an industrial scale in the 1930s, the first use was in China around 600 BC (where Gigartina was used) and in Ireland around 400 AD. There is some disputed evidence from animal studies which indicate that degraded carrageenan might cause gastro-intestinal cancer.
The largest producer is the Philippines, where cultivated seaweed produces about 80% of the World supply. The most commonly used are Cottini (Eucheuma cottonii) and Spinosum (Eucheuma spinosum), which together provide about three quarters of the World production. These grow at sea level down to about 2 metres. The seaweed is normally grown on nylon lines strung between bamboo floats and harvested after three months or so when each plant weighs around 1 Kg.