Properties of Alginate
Roughly speaking the M to G ratio of the alginate largely controls functionality. Work has shown that a more sophisticated approach linking gel properties to block size produces a better correlation. Higher G containing polymers tend to form more rigid gels at a very specific concentration of cations whereas higher M polymers tend to form softer gels and over a wider range of conditions. As alginate is a linear polymer the viscosity is determined by the molecular weight and the rigidity and extension of the chain.
|Shore cast Laminaria|
The most common alginate gel used is the calcium alginate gel. Alginate will gel with most di and trivalent salts but the calcium gel is really thinly one used in the food industry. The texture of a straight alginate gel is not very good for a lot of food applications but has found a niche in the area of restructured products such as fruits and meats. Alginate is also used as a stabiliser for the ice cream industry.
One advantageous property of alginate is in the ability to formulate controlled set gels by manipulation of the calcium ion availability. This can be used in cold whip products where the gel set is delayed by a few minutes until the alginate is dissolved.
PGA (propylene glycol alginate) is the only, commercially available, chemically modified alginate. PGA is made by contacting a partially neutralised alginic acid with propylene oxide gas under pressure. The propylene oxide reacts exothermically with the alginic acid to form a mixed primary/secondary ester. The PGA market can be split into two main areas: The highest clarity and ester content PGA is used in the beer industry as a head retention aid. Lower grade products are typically used in salad dressings, in conjunction with xanthan gum and fruit juice based products as a stabiliser.