Alginates

Alginates are made up of long chains of two monomers guluronic acid and mannuronic acid. The chains can be made of all one monomer or mixtures of both. 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 carrageenan, another seaweed extract, the ability to bind to calcium makes alginates 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. It is used to preserve the foamy head on beers. 

Alginates.—In a historical series of articles on the development of the seaweed industry, the first article has considered the use of alginates.  

The oxidation of alginate chains with periodate has a marked effect on the intrinsic viscosity of the alginate but the authors consider that previous values may be incorrect due to errors in measuring the molecular weight of the original alginate.  

Polarimetry of the brucine salts of L-guluronic acid and D-mannuronic acid released from alginates by acid hydrolysis has been used to measure the ratio of these acids in the native alginate. Nitroxide spin-labels have been investigated as molecular probes to determine the microviscosity of aqueous solutions of carbohydrates such as alginate.  

4-linked D-galactose residues in these polysaccharides. These carrageenans were, to a large extent, -like but did have some A-like features. Differences between the two carrageenans were observed in their i.r. spectra. The A-carrageenans from Irideae cordata and Rhodoglossum californicum differed from that of Chondrus crispus to a small extent and these differences were not due to the 6-sulphate content. 

Carrageenans were partially hydrolysed when sterilized in a synthetic milk salt solution. The reduction in the molecular size of these polysaccharides did not occur when heated in aqueous solution at neutral pH values and was caused by a lowering of the pH which occurred with heating in the milk salt solution. 

Vijaya et al. (2008) stated that at trivial conditions physiochemical properties e.g. porosity, degradability of alginates can be altered very easily, which can improve efficiency of heavy metal removal. 

Adsorption capacities of different adsorbent was compared by Choi et al. (2009) modeling using Langmuir adsorption isothermal model (Eq. 2.1) and three stage kinetic model as shown in Eqs. (2.2) and (2.3) below. 

C(t) and C(o) is the aqueous concentrations at time t and initial stage, V is the solution volume, M is the mass of adsorbent, SI (oo) and S2 (oo) are the adsorbed concentrations for both the types of kinetic models respectively. Mass transfer rate from solution in both the types is shown by a and b is defined as a limiting factor for S2(l) with its range 0 p 1 (Choi et al. 2009). 

Park et al. (2007) calculated Langmuir adsorption isotherms parameters for various heavy metals comparing both alginates and activated carbon shown in Table 2.3 (Park etal. 2007). 

Mixing precursor with chemicals H3PO4, KOH, NaOH 

Alginic acid is a linear multiblock copolymer from blocks of jS-(l- 4)-D-mannuronic acid and a-(1 4)-L-guluronic acid, as well as alternating copolymers from these two monomer units. In natural products, the molecular weights reach about 150,000 and with regenerated products 30,000-60,000. Alginates are the salts of alginic acid. 

Alginic acid is found in brown algae, where it acts as an ion-exchange agent in the cell walls. It is obtained as alginate in England, France, Norway, Japan, Southern California, and Australia by extracting the cell walls with soda solution. 

A reaction with propylene oxide produces the nontoxic propylene glycol alginate, which, unlike the alkali alginates, does not gel at high concentrations. Typical uses are as stabilizers for puddings, ice cream, orange juice, beer foam (in the United States), inks, cosmetics, etc. 

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Mixed alginate salts Mixed catalysts Mixed cellulose ethers... 

Alginates, alkaloids, glycerides, gutta, phenols, rosins, rubber, saponins sterols, tall oils, tannins, terpenes, waxes... 

Algin occurs in all members of the class Phaeophjceae, brown seaweed, as a stmctural component of the cell walls in the form of the insoluble mixed calcium, magnesium, sodium, and potassium salt of alginic acid. 

Table 4. Composition of Alginates from Different Seaweeds...

The viscosity of algiaate solutioas is iadepeadeat of pH ia the range 5—10, but below pH 4.5, the viscosity iacreases uatil the pH reaches 3 whea iasoluble alginic acid precipitates. Propyleae glycol algiaate is soluble and stable at pH 2—3 but not above 6.5. 

The flow properties of sodium alginate solutions depend on concentration. A 2.5% medium viscosity sodium alginate solution is pseudoplastic, especially at the higher shear rates in the range of 10—10,000/s. 

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