Final answer:
Alginate hydrocolloids undergo two main reactions when mixed with water: dispersion of hydrophilic particles in water to form a colloidal system and gel formation through ionic cross-linking.
Step-by-step explanation:
When alginate powder is mixed with water, the creation of a paste involves two main reactions.
Firstly, the alginate particles, which are hydrophilic, disperse in water to form a colloidal system.
This is possible because the alginate particles, like other hydrocolloids such as starch and gelatin, have surfaces covered with polar groups that interact with water and prevent aggregation.
The second reaction is gel formation, where calcium ions present can cross-link the alginate chains, resulting in a three-dimensional network that traps water, forming a gel.
This mechanism is similar to the gelation of pectin in jelly making or the setting of gelatin in desserts like Jell-O.