|guluronic acid||mannuronic acid|
Alginates is made up of long chains of two monomers -- guluronic acid and manuronic acid. The chains can be made of all one monomer, or mixtures of each. The stems of kelp are made of chains with more guluronic acid, and the leaves (fronds) have more mannuronic acid. Guluronic chains bind tightly to calcium — in mannuronic chains the calcium is more easily replaced by sodium, allowing the fibers to swell easily.
As with carageenan, another seaweed extract, the ability to bind to calcium makes it useful in dairy products as a thickener. It also makes alginates useful as wound dressings, where they absorb fluids, and stop bleeding, and act as a scaffold.
Alginates are used as thickeners in fat substitutes, pet food, stuffed olives, onion rings, low fat sauces and spreads, and pie fillings.
Propylene glycol alginate is stable in acids, and is used to keep the foamy head on beers.